to please go ahead and begin whenever you're ready. Thank you so much, Mike. This is Kristen Lees at Heritage Preservation. And welcome back to our course caring for photographs. This is our third webinar in the series. And we want to thank Learning Times, again, for their help in producing it, and to the Institute of Museum and Library Services for the funding that makes this possible, and makes this free of charge to everyone. I want to also thank Greta Glass for joining us today. She'll be in the Q&A box, helping to answer your questions during Debbie's presentation. So welcome back, Greta. Again, this is our third webinar. And this is the second part of our technological development of photography. And we'll get into more of the negative processes today. And we'll have two more webinars next week on Tuesday and Thursday. And this will be back to the regularly scheduled time of 1 to 2.30. But thanks again for adjusting your schedule and to join us a little later today. Again, the course web page is up to the place you can find the PowerPoint from today's presentation after the class, links to the homework, and a great bibliography of resources that we hope you'll take advantage of. And remember also that we have a handful of publications that are available through the Getty, and they're offering a 30% discount. And I've added that information in the course page as well. So after the whole course concludes, we will be putting the recordings on this page. In the meantime, look for emails from us that give you the recording link after each class has aired. And just remember that Thursday, May the 30th, is our deadline for completing all of the homework assignments or watching any webinars that you've missed. So if you meet that deadline, you'll be receiving our certificate and digital credential for this course. If you have any questions, always let us know. It's at info at heritagepreservation.org. And the emails we send to the group also come from this address. So make sure that it's a safe sender in your email. And Debbie has offered to look at photographs that you have in your collection, either things you think are interesting and are very significant to your institution or things you have questions about, or there's damage. And she would welcome you to send those to her until continue to include them in her PowerPoint presentations, especially in her final presentation, which will be on Advocacy for Preservation. And we put a Gmail address up here just because we can handle larger attachments to our Gmail account. So I'm putting it up here. But if you're having any trouble getting attachments to us, just always shoot us an email at info at. And we will work with you to get those files. But I wanted to say, you know, we've looked at the homework assignment you did for last time, which asked you to use the graphic atlas to identify a photo print in your collection to suggest what would be needed to care for those photos and to tell us the significance. And there are some really great stories. So thank you for all of those who've done that homework. And this would be, you know, some of those stories are so interesting about the significance, and those would be great examples to send on to Debbie. And we'll share those notes with her as well. So I want to welcome back Debbie, but first we were going to just do a poll just because we're today, we're going to be talking about negatives. And there's a handful of categories. We thought if you're aware of them, if you could check off what types of negatives you have in your institution. And don't know is a fine answer. If you're not sure, you will learn today. So just give Debbie a heads up on what sorts of things you might have and then she might change how she will address them. But it looks like a great mix of all types. So that's useful. Okay, I'm gonna try to squeeze another poll onto our screen. I hope everyone can see this and just sort of getting an estimate of the quantity of things that you might have. I'm sorry, I'm just gonna resize this a bit. See if we can squeeze it in. Hopefully you can see all of that. So, and if you don't have any negatives, I see Cindy's asked. That's fine too. There I think there's lots, Debbie will be reviewing prints and there are lots of, I think, applicable tips and information that will be related today. So great. Okay, well I'm gonna close these and then I'm going to drag away the poll box you've been chatting in and we're gonna change that with a moderated chat that Mike mentioned. But feel free to keep going with any questions or welcome. And Debbie, I'm just gonna pull up your PowerPoint here. And there you go. I'll turn it over to you. Thank you. Now Kristen is that, okay now it's a full screen. Hi everyone, I'm happy to be back for webinar number three. Thank you all, those have done the homework. It's been most interesting to follow it and as Kristen said, it's really great if you can send images if you have questions because I then can try to incorporate them into the presentation where they might fit and relay real stories and try to address real problems that you all are facing. But it's been a lot of fun. I have enjoyed this form of teaching. It's very different from what I'm used to but I do love the fact that we're reaching such a wide audience and that's been most rewarding. As you probably learned, I'm a huge Beatles fan and that's why all of my lectures have started with a Beatles song and this one helped. It's probably most appropriate for 19th to 20th century photographic negative materials from a poll it appears that many of you have a wide selection of these materials from glass plate to film based negatives and in many cases, large numbers as well, over 10,000 in many of your institutions. So we're going to focus today on photographic negative materials and talk a little bit about how to identify them. And next week on Tuesday, I will be talking more about preservation planning, handling, proper storage, some of the questions that have been emerging throughout the homework assignments and during the conversations in the chat box, et cetera. But most importantly, what are you seeing here? This of course is Sir Paul McCartney in Cincinnati, Ohio, almost two years ago, August 4th and a date that's significant to me. I have seen Paul McCartney now 17 times I think and he's on tour again this summer which I'm most excited about. My oldest daughter's getting married in June, June 21st and having a big party in July so I have to work around those dates. But I certainly hope to follow him as well in some of his concerts. But in Cincinnati on August 4th, 2011, at this concert, I actually had an opportunity to meet Paul McCartney briefly but it's a memory that I will always treasure. And so I thought I would share one more picture with you and then get on to what's important. So let's see, let me find the pointer. Hang on, there it is. Okay, this is me actually here. Prior to the concert, my husband surprised me and brought me 4th row seats and here's my sign and I showed it to you because of this photographic, or these of course are copies of photographs, but these are images of Paul McCartney from 1966 when I actually saw him with my father in a concert in Philadelphia. I had the greatest sign, the sign opens up, it has fire, all kinds of streamers and hearts and actually he saw it, he nodded and smiled and during the concert it was actually featured during one of the songs. So it was a moment of enormous happiness for me. So anyway, I share that with you. But I know that you're not here to learn about my love for the Beatles, but rather to learn about photography and what I wanted to do, I don't wanna rush through this material and I felt like we may have rushed a bit too much in the second webinar especially, trying to deal with all of these photographic printing processes. There's so many of them and I know we were going through them quickly and I could tell from some of your comments that some of you were getting a little bit confused which is totally understandable. Hopefully by going back and using the graphics at last and thinking about your collection, some of this is clear now, but I thought it would be worth taking 10 minutes or so and just reviewing some of the high points of the talk that we had last week as it relates to photographic print materials and this slide particularly is important in that again, it begins to give you a sense of the chronology of these print processes because there are so many of them. And so if you begin to appreciate what processes were popular when and then you look at your collection, this will help you at least narrow down the possibilities. Do I have a Silver, Gelatin, Black and White photograph or is this a photograph from the 19th century? So I wanted to share with you this timeline which of course you've seen already as well as this which is another one. This one's sort of interesting in the way it's designed in that it's subtle, but the line that the, I'm gonna trouble with the pointer. Hang on you guys. Anyway, I'm having trouble with the pointer but I don't really need it. But the line that goes through the center of the slide shows you the, from which the numbers are sort of building on. You can see that it changes color, it goes from brown to black to the dyes and that is a reminder to all of you about what that final image material may be. In the 19th century we talked about how these early papers were printed out by taking light sensitive paper, placing it in contact with the negative and out into the sun until the image actually printed out, creating an image that's more purpleish black or brown in color and you can see here that these early photographs, salted paper and albumin are browner in tone. In the 20th century in the 1900s you began to see the introduction of Silver Gelton developing outpapers, papers that are produced in a dark room with the final image being more black and white as you can see here.  But then finally in the 1960s the introduction or the popularity of color photographic processes in which the final image material is actually organic dyes exemplified by the cross-section of cyan, magenta and yellow. So these dyes that fade at different rates in the dark and in the light and therefore images may appear magenta as you see in the image toward the top of a fly. So again this image, this particular size can be very helpful not just for the chronology but even you get a sense of the image color which you can begin to associate with your collection. So just to review the process that dominates the 19th century which many of you certainly have whether you're located in Bogota, Colombia or Belize or Scotland or Sweden, China, Japan is the albumen process and this photographic process dominates the 19th century. It's a printed out process that's made on a lightweight piece of paper that's coated with egg white or albumen and it's printed out in the sun. The final image is silver, silver metal we call it photolytic silver or silver produced by light and these albumen prints were typically toned with gold. They do deteriorate as you can see in this example from the University of Texas School of Law which was submitted online in that all these albumen prints are somewhat yellowed and faded and the yellowing in the highlight area you see at the outer edges of these portraits is caused by the deterioration of that egg white binder because the egg white does yellow and deteriorate over time. So you're seeing an overall yellowing which is the degradation of the binder layer and also a certain amount and all these images really of image fading which is a deterioration of that silver image. So the silver which is originally more of a dark perhaps purplish black in color as it deteriorates it becomes brown or lighter in tone. And so you're seeing here some of the characteristic deterioration problems that we associate with the albumen process. In comparison, oh and let me go back for a minute and just mention something else. We talked last week also about these different layers, a one layered, a two layered and a three layered structure with the photographic print materials. The albumen process is an example of a two layered structure, a lightweight piece of paper coated with this egg white binder. So when you look at it under magnification on the graphics atlas for example, you will see paper fibers. You'll look through this transparent binder layer but they're somewhat muted. They aren't as visible as something like the salted paper print or the cyanotype or the platinum print where the image material is embedded directly in the paper support. The other thing that you may see with albumen prints that's characteristic is a cracking or crazing of that egg white binder which occurs as it expands and contracts differently from the paper support. So this is a two layered structure, again a process that dominates the 19th century. In comparison, compared here with a photograph that's much glossier in tone and under magnification, it appears to be very smooth. This is a silver gelatin printed out paper. And so in this case, we have a silver image again that's produced in the same way that the albumen print image is produced by placing this light sensitive paper in contact with a negative and out into the sun. Like the albumen print, this is typically gold toned. But the difference is that the paper support is coated with that burrida layer that we talked about, that white pigment barium sulfate added to gelatin coated on the paper to produce burrida whites and a smooth surface. So we refer to this as a three layered structure. Like the albumen print, these photographs can fade and discolor. The highlights, however, do not typically yellow like the albumen print because this is gelatin as a binder as opposed to albumen or egg white. So it's a matter of maybe reviewing some of the slides and certainly looking at the resources going back to your collection and thinking about what is that print, how is it made, what is the layered structure, what is the image tonality. And here's one more example. In this case, an image that is much more black and white in color, almost greenish black really at the top of the photograph. I'm gonna try that pointer again. I'm on a different computer and I don't really know why but I can't seem to get the pointer to work and every time I try it, I lose my talk. So I'm not gonna do that anymore. But anyway, hopefully you guys can, if I explain where I am, now it's moving better.  This is a silver gelatin developing out photograph. So this is an example of a photograph from the turn of the century where the photograph is actually produced in a dark room and not produced by light. And we also mentioned not to confuse you all too much but in the 1920s, 1930s, 1940s, some of these black and white photographs were actually toned with sulfur to produce a brown image that begins to resemble some of the Albumin prints in the silver gelatin printing out papers. But this is actually a black and white paper that's intentionally toned with sulfur to produce what we call a sepia-toned or sulfur-toned photographic print. These are very popular in the United States particularly and they are typically in very, very good condition which is certainly true of this wonderful portrait that you see here. So just to summarize, in terms of photographic printing processes, and this certainly is important with negatives as well, there are many things to think about when you're trying to distinguish one process from another and they're listed here in the slide. Is the photograph highly reflective or is it very matte? If it's very matte, the image may be embedded in the paper support such as a salted paper print or highly reflective that might tell you that there's actually a brighter layer there. It could be silver gelatin printing out or silver gelatin developing out paper. What is the tonality? Is it brown in color? Is it black and white? Recognize that we've only talked about some of the processes. There's so many other photographic processes so image tonalities can vary but generally you might look for something that's brown or a purplish brown versus something that's black and white. What does this object look like under 30x magnification? And you can buy handheld magnifiers at stores that will magnify with an internal light up to 30x and this can help you in distinguishing some of the characteristics that we've spoken about. How is it mounted? Sometimes the mounting style can help you differentiate at least decades or centuries and so that's something to certainly think about as well. And then certainly deterioration problems such as image fading, binder layer cracking which we see with albumin prints particularly or abrasion which is very common with collodion photographs such as matte collodion or glossy collodion material. So hopefully this may help you a bit if you're still struggling with all these different processes I can promise you that it just takes practice and time and thought and looking at your collections and going back to some of the resources that we've provided. Last week we shared with you a number of different books all of which are truly excellent and we mentioned this book but I didn't have a screenshot so I wanted to share the screenshot here the Karen identification of 19th century photographic prints by James Riley of the Image Permanence Institute. This is another great resource that some of you actually pointed out in the chat box and I want to be sure you at least got a sense of what this book looks like and what's really nice about this publication is it's accompanied by a chart which you can see only in a very small format here that again an identification chart that using this layered structure approach is it one, two or three layers? Is it photographic or photomechanical? And then you follow through with what the photograph looks like how it's deteriorated. You will, this will help you in differentiating some of the processes. If you'll remember the very first webinar we spoke briefly about photomechanical versus photographic and that's an important distinction that you really must make in looking at your collection early on is it continuous tone or not and here's just another, there's many different resources out there. Galen Weaver who's in private practice in San Francisco, I've mentioned him in his work with Silver Gelatin papers last time. He's developed yet another way of sort of identifying processes with 19th century materials looking first at image color. And so these approaches vary and in the end what I tell my students really all over the world is you need to develop your own approach. You need to look at photographs, think about the issues and determine what's the best way for you to identify these processes. So you have much to work with and I think that's all very good. One more I keep throwing in into these presentations online resources that I think are helpful and I hope will be helpful to you and this is one that we haven't mentioned yet. So I just added it here, the Library of Congress and some excellent resources that they have on photographic material identification, deterioration and preservation. So certainly take a look at that as you can. So with that I think, I guess before I move on to negatives, Kristen I'll ask you if there's any questions that have come up in the chat box or in the parking lot that I could answer now and if not then I'll just start with negative materials. Well, quite as keeping up with all of the questions, I think so far I'm just... Okay, well if that's true, let me just keep going. Sure. Thank you. You're doing a great job and it's an enormous help I know to all these participants. So let me keep moving forward because we have a bit to cover here with photographic negatives. And the photographic print processes, I'm going to review these in sort of a chronology. I'll talk a little bit about negatives more generally. We'll certainly talk about resources which may be what's most useful to you. And then a little bit about some of the different processes that you're likely to encounter in your collections. What you see here is an excellent example of a cellulose acetate film. Cellulose acetate is introduced in around 1924, still being used today in various acetate films. And one of its greatest preservation challenges is that over time, the cellulose acetate film base will shrink. The gelatin emulsion does not. And you get this characteristic channeling which you can see very clearly in the negative here. So the other thing that you notice in this particularly negative perhaps, and it may depend on your monitor, but I just want to point it out because it's interesting here. Some of you may see that the negative in some areas has sort of a bluish tonality to it. And this is another deterioration problem that's associated with an anti-halation dye that is in the anti-curl layer, on the back layer of the negative. And over time, this anti-halation dye is regenerated and becomes sort of bright blue, as you can see here. This is a real issue in emergencies because following exposure to high pH and immersion in water, these dyes can be regenerated and these acetate films can become very bright blue in color. So that's what you see here. But the most important point is that this is a cellulose acetate film. And we'll talk both about cellulose acetate and also cellulose nitrate, film-based materials, as well as glass plate negatives briefly, and this is an example of a glass plate negative that you're actually seeing, obviously, as a positive. But generally, in very, very good condition from the Missouri State Archives, there is some damage in the background above the sitter's forehead. But generally, I would say that this negative is in good condition. Now, in terms of resources, there are many, and we've got them listed, many of them are listed on the website, so you should look at that. This is what I want to draw particular attention to. It's a wonderful booklet written by Maria Fernanda Valverde. Maria Fernanda teaches in Mexico City. And this booklet, which she's written, which is comprehensive and goes into enormous detail, very clearly written with wonderful illustrations, is available online. You can download it through the Image Permanence Institute website. And so this is free of charge and a resource that I recommend very highly. Of course, some of the books that we've already talked about have excellent sections on negatives as well as prints. So you want to look at those as well. Now, when you're dealing with photographic negatives, one of the greatest challenges really early on was to try and determine what is the most ideal material for a photographic negative. And ideally, you want something that's transparent because you're going to be using it for printing. And photosensitive, so that it's reactive and your exposure times are minimized. You want it sensitive to all colors, not just sensitive to blue or red light. Easy to use, lightweight and flexible, and chemically and dimensionally stable. Unfortunately, many of the processes that we talk about are not necessarily chemically or dimensionally stable. They may not be lightweight and flexible, and they weren't always easy to use or sensitive to all wavelengths. But that's sort of the ideal material when you're talking about photographic negatives. What you're seeing here is a paper negative, a waxed paper negative. These were some of the earlier calotype negatives, the earlier negatives that were produced. And you can imagine that if you take paper and you wax it, that your transparency will be minimal. And so these are difficult to use, but it was really the only option early on. And they were used in combination with the salted paper process to produce a salted paper print, which you see here. So here is the salted paper print made from that waxed paper negative. And as we talk about negatives, we'll often talk about the print processes that were commonly used with that particular negative process. So again, this is an example of a collodion wet plate negative. This negative that you see here is actually on glass. Glass replaced paper by the 1850s. And I'll talk about that chronology in a minute. When we look at cross-sections, we spend a lot of time talking about that. Often you have a paper support and those silver particles may be embedded or as you see here in that paper support, which would be true of a salted paper print. With a gelatin with a more common, a more contemporary negative process, you can see that that cross-section becomes much more complex. You have, as you see here, a polyester film support with gelatin on either side, an anti-curl layer to prevent that film from curling, and a gelatin layer on the other side with the silver particles. So these layers, this layered structure, when you're getting into negatives can be quite difficult. And here's an example of a contemporary color dye negative in which you have, again, a polyester film support, an anti-curl layer, which is common with film-based materials after about 1903. And then the final image in this case would be comprised of organic dyes, cyan, magenta, and yellow. So these cross-sections are important to keep in the back of your mind, and I'll go back to them again as we talk about some of these processes. But in terms of the chronology, the earliest negative materials were these paper negatives, these waxed paper negatives, as you see here, introduced in 1841 at the same time as a salted paper print used for printing salted paper and used, really, until about 1865. You probably do not have many, if any, early paper negatives in your collections. These are relatively rare. You may find them in major museums and fine art collections, certainly, but not as frequently in his library's archives, historical societies, historic health museums, et cetera. The paper negative is soon replaced, really, with glass as a support. Of course, glass is much more transparent than wax paper. And the first glass plate negative process was the collodion on glass. This was introduced in 1851, and if you think back to our very first webinar, we talked about direct positive processes, and we talked a bit about the amber type, a photographic process on glass. The collodion wet plate negative and the amber type are very, very similar. But in this case, you're dealing with a negative image. Remember, the amber type was actually a negative image, but it was a very thin negative image, and it was made to appear as a positive by coating a black lacquer on the back of it. With the collodion wet plate negative, which you see here on the left of your slide, in this case, you don't back it with anything because you want to use it as a transparent support. The collodion wet plate negative is replaced by the end of the 19th century with the gelatin dry plate negative, which you can see was really popular until 1925. The collodion wet plate negative is made by hand. You have to pour the collodion onto that glass support. The dry plate negative is produced by machine, and so it was much easier for the photographer to use. And of course, without telling you anything, without going into any more detail, you all could tell me immediately the biggest difference between these processes is the presence of collodion with the collodion wet plate negative. Remember that binder, which is the formacellus nitrate, compared to the presence of gelatin as the binder in the dry plate negative. Gelatin is a commercially prepared protein. And it's called dry because the negative is purchased. You didn't have to worry about keeping that gelatin wet. Whereas the collodion wet plate negative had to be produced before the collodion actually dried out. And therefore, we refer to it as a wet plate collodion negative. Glass was a wonderful support. It was transparent and certainly superseded the waxed paper, but it was fragile. It was heavy. It was difficult to transport. And by 1889, we see the introduction of flexible film for cellulose nitrate, popular really used until 1950, particularly for professional motion picture film. The introduction of cellulose acetate in 1925 and then polyester film in 1955. And so this is sort of, you know, hopefully a helpful chronology for all of you to give you a sense of the evolution. And now you can think back to your negatives and begin to differentiate when one process may have been introduced versus another. I don't want to spend time really on the paper negative process because I don't think many of you have these, but I've been here just to give you a little bit more information. So this is a silver image, actually, embedded in a paper support, but the paper support is waxed to make it more transparent and translucent because from this wax paper negative, you would typically make a salted paper print. Like any silver image, and we've seen so many examples in the last two days or last two webinars, these silver images can fade into color and certainly that's true with negatives as it is true with positive prints. So a lot of the deterioration mechanisms that we've talked about in detail with the photographic print processes relates and correlates to the negative materials as well. Now, again, in 1851, we began to see the introduction of glass as a support in photography, both for the amber type, as you see on the left, and the wet plate collodion on the right. In this, and here I would urge you, we've talked a bit about, and I know Heather and Greta, both in the chat room have mentioned that you can find films online at YouTube and also at the George Eastman House site showing how to make some of these different processes. And I urge you to take a look at those because it will make this very clear in terms of the many steps that are required to produce something like a wet plate collodion negative, which you see being made here. You take a good, clean piece of glass. The glass is typically cut by hand, and so when you're trying to distinguish a collodion negative from a gelatin dry plate negative, sometimes you can just look at the glass as it hand cut or cut by machine. Usually a thicker piece of glass with the collodion wet plate negative, and the negative then is clean, the glass is clean, and the photographer would pour on a solution of collodion or say, let's nitrate, a very viscous solution almost like the viscustia of honey, to which something like cussium iodide or some kind of iodide salt have been added. That plate then, while it's still damp, is immersed in a silver nitrate bath to produce light-sensitive silver iodide or light-sensitive silver chloride in that collodion binder layer, which would then be placed in an exposed to light. All of this work has to be done before the collodion dries out, and that's what it's known as a wet plate process. Once the collodion dried out, you could no longer process the image, and so it became very difficult and cumbersome and photographers who were photographing landscapes outdoors had to bring with them the whole dark room, their glass plates, the collodion, the silver nitrate, the varnishes to varnish the plate after printing, and all of this was done on site, which is why the dry plate when it was introduced at the end of the century was so popular because it didn't require that kind of manipulation. The collodion, again, dates of popularity, 1851 to 1885, and here you see a collodion wet plate negative probably taken with a camera that had two lenses. But what's interesting, and what I love about this example is that you can see that the young girl to the right of the slide, that negative appears to be in very good condition. There are some abrasions and scratches, but for the most part, it's in excellent shape, whereas the negative image at the left of the slide is much more faded, yellowed, and deteriorated. You can see the silver image deterioration at the outer edges and a lot of abrasion and a lot of degradation. And I suspect that what you're seeing here is that the image to the right has been varnished, and the photographer sort of poured the varnish on to protect the collodion image, which was part of the process at the end of producing these negatives, but did not, intentionally did not varnish the other image, had already decided that they would only be printing the one image. And so you can see the protective nature of varnish, how that has protected the silver image from deteriorating and fading on the right, where it's much more faded and the collodion is much more abraded on the left. And here in fact is a positive, the same image seen in positive light, and you can see, you can still see the image certainly, but the image on the left is much more deteriorated than the image on the right. The wet plate collodion negative was used primarily with albumin prints. And so there is almost a marriage between the negative process and the print process, the calotype, wax paper, negative, with the salted paper print, the collodion on glass or collodion wet plate, negative printed with the albumin paper, which you see here. But what I'm showing you here is in the detail, is retouching, which you begin to see with photography in the, with the introduction of these glass plate negatives, and the face is heavily retouched with graphite pencil. This is done as these portraits become larger. So you begin to see the cabinet cards that we talked about last time, these images that are about four and a quarter by six and a half inches. The faces are larger, the faces are more prominent, and the sitters want their faces to appear in a certain way, and photographers begin to retouch the negative using graphite pencils. So sometimes in your collections, and this is true with all glass plate negatives, if you look carefully at the faces, you'll see they almost look like they've been varnished, and then retouched with a pencil. And in fact, that's exactly what's been done so that to improve the appearance of the final print. Let me talk about the dry plate, and then I'll take a break and answer any questions that may have come up before we move into film-based materials. The gelatin dry plate is something that you have mentioned, many of you mentioned you do have in your collections, and this comes, this image, it's really a fantastic image from the North Carolina Museum of Natural Sciences. Notice, of course, that this negative, which is in relatively good condition, is being handled with gloves, which is certainly the right thing to do, although some people feel strongly that they are, can handle these materials more safely if they don't wear gloves. And that can be done as long as you don't touch the surface of the emulsion and only touch the edges of the glass, but gloves, either latex, vinyl, or cotton, are preferred. But just looking at this, you can see a black and white image, very similar in some ways to the silver gelatin developing out paper, because like the developed out paper, you know, this is produced through chemical development. The final image material is metallic silver, it's a filamentary silver, and when these images are in good condition, they appear very black and white. As they deteriorate, they may become more brownish or yellowed, and that's often at the outer edges, because that deterioration is accelerated by exposure to high relative, high temperature conditions. These dried plates are typically sold in boxes, as you see here. Again, photographers no longer had to coat the plates or make them light sensitive, they were already light sensitive. And many collections are still storing their negatives in these boxes, which is not ideal, because the boxes are giving off oxidants and pollutants that will cause the silver images to fade. On the other hand, sometimes these boxes have enormous historical value, and they have inscriptions where they're just important and interesting for the information they contain. So it's not that they should be disposed of, but ideally, it's best not to house your negatives in those historic boxes. The dried plate negative itself is gonna have a smooth surface. It will be machine cut, because this is all done by hand, black and white in color when they're in good condition, but as is true with every silver process that we've talked about, these materials can fade and discolor, and they do, upon exposure to poor environmental conditions. Another challenge, really, with dried plate negatives is the deterioration of the gelatin, and more importantly, it is the fact that it's very hard to adhere gelatin to a glass plate support. So sometimes you will see flaking at the outer edges. Here's an example of a silver gelatin dry plate negative in very good condition, black and white. There's some staining and yellowing, certainly, that we see that could be caused by exposure to a poor quality enclosure, but generally, this is in good condition. Whereas this one is beginning to illustrate some of the gelatin-related problems that I mentioned, the gelatin at the outer edges is really becoming detached, it's beginning to lift and flake, and in this case, this particular object would really have to be separated, stored flat, and brought to the attention of a conservator to see if it's possible to consolidate these large flakes of gelatin. Here's another example, this one from the Smithsonian Institution Archives provided by Greta, and in this case, the negative is in relatively good condition, but it is beginning to flake locally. You can see at the lower right corner, for example, and that's another example of deterioration that's really caused by the gelatin. The silver image perhaps is faded, it's a little browner or reddish in color, but the main challenge with this particular dry plate is that gelatin binder degradation, which you see in two spots, particularly on this image. Finally, in this sort of category, I wanted to be sure to mention, because this came up a number of times, is the issue of lantern slides, and some of you will have very large collections of lantern slides. These can be a variety of different processes, but many of them are actually gelatin dry plate positives, and so it's actually gelatin on glass that may or may not be hand colored, in this case, this image provided by the Missouri State Archives appears certainly to be hand colored. Sometimes the coloring is printed, but I suspect this is hand colored. And so this is a gelatin emulsion on glass, like a dry plate negative, but it's a positive image that's been hand colored, and then protected on the emulsion side with another piece of glass and a decorative mat and taped around the outer edges. So your lantern slides in your collection are going to more closely resemble these dry plates, and the deterioration problems that you see with your lantern slides will be very similar to the kinds of problems that we see with dry plates. Fading of the silver image, sometimes mirroring, which we saw certainly with black and white photographs, happens quite extensively with dry plate negatives and also lantern slides, when the seals are broken, when the paper tape has begun to lift, and you begin to get air and moisture. You also will see something I didn't have on my list that I should mention, and then I'll take a break, is glass decomposition. You recall, if you go back when we're finished and maybe skim through the first webinar, which was more of an introduction, but I showed you some examples of glass decomposition with the early daguerreotypes. Glass, transparent glass, can deteriorate over time. When you have stacks of lantern slides or stacks of dry plate negatives, sometimes you will see evidence of deterioration of the glass, either the cover glass, in the case of a lantern slide, or even the glass support itself. And so that's something to be aware of. Before I move into Silas Nitrate film, let me just take a brief break. I don't wanna take too long of a break, because maybe we can actually get through all this and then do more questions at the end, but Kristen, are there questions that are coming up that I could address? Okay, well, let's handle, Greta's doing a great job, but let's just handle a few that are sort of similar. Okay, how do you attempt to do any kind of cleaning on a negative, either if they're glass, would you do any dusting of them? If they had a fingerprint on them, could you do any cleaning? Yeah, that's a good question. Well, first of all, just like photographic print processes, you need to know what that material is. So let's say you have glass plate negatives that are dirty, that have some sort of dirt and grime, and you wanna duplicate them. So you'd like to try and do some minimal cleaning if possible.  That's the first step, to really firmly understand what you have. But I would say that you can safely clean the backside, the non-emulsion side of a glass plate negative, using a soft cotton ball, for example, and removing some of the dirt in that way. You probably wanna avoid cleaning the emulsion side, the image side of these negatives, because you can cause damage. The gelatin, if it's a gelatin plate, it can begin to lift and crack. You can use certainly a soft brush and remove any particulates in that way. That should be safe with a gelatin dry plate negative. It may be problematic, however, if there's flaking of any kind. So I would avoid any plate that has that kind of damage. For the plate that appears to be relatively intact, whether it's collodion or gelatin, you could use a soft brush. Anything beyond that on the surface, I personally would avoid, because of the fragility of these emulsions. They're very thin, and they are not necessarily well adhered to the glass plate support. Okay, Lynn had a question about, is there anything you can do to stop flaking? So I guess, obviously, before you use any brush, you don't wanna make sure there's no flaking. Yeah. The flaking is caused by exposure to fluctuating environmental conditions. Sometimes it's just at the outer edges. And the best thing you can do, really, is to try and house these collections in a stable environment. And at least that will mitigate against further flaking. Plates that are severely flaking should be held flat and separated from the other materials, because really, the flaking is exasperated by handling. So you wanna try to set them aside. What you're typically doing with these negatives is preparing them for duplication, digitization, or whatever you might be using in your institution. So there is a desire to try and clean them to the extent possible, because you wanna get the best possible copy. In some cases, if you're doing a large digital project, it may be worth hiring a photograph conservator who could come on site and examine the negatives and perhaps provide some training on other cleaning techniques that could be used if the collection's very dirty, and that will impact on the quality of the duplicate negative or digital process that you're using. Okay, and Nicole in Boulder mentioned what if it's a cracked piece of glass? And Greta had recommended doing some type of a scan, a careful storage. Is that what you'd... Yeah, I certainly think that is absolutely right. And it's really remarkable what you can do now with digital imaging, which was never an option when I entered the field many, many years ago. But you can scan pieces and you can create a surrogate negative that looks very, very good, and from that you can make a print. They actually, you always wanna preserve the original, and the original can be preserved in perhaps a sink mat of some kind that would hold the pieces separate. You don't want the pieces to rub against each other, or wrapped in acid-free tissues, something that will hold those fragments in a safe way. There are techniques that are used by conservators from time to time to actually mend broken glass plate negatives, but that's typically done for those negatives that have very high value, because it's just not necessary. You can do an awful lot through scanning. But just when you get involved in copying of these negative materials, do not make the mistake. The focusing entirely on the copy and not preserving the original, however damaged it might be, you need to think about what can I do to minimize handling and to protect the original object from deterioration? Okay, and Angela asked a great question. I know it's something I've dealt with my personal photographs at home, and probably others have too, that the negatives often have some tackiness and can stick together. What do you do if you come across a stack of negatives together? Well, that's often true with a stack of gelatin dry plate negatives, for example, because again, you've got this gelatin binder, this commercially prepared protein that swells upon exposure to humidity. And so they can all start to stick together in the same way that a photographic album can stick together. It's the gelatin again, particularly a challenge after a disaster when things have gotten wet. And in that case, I would say, in some situations, unfortunately, there's nothing that can be done. But before giving up all hope, they really need to be brought to a conservator who can begin to investigate how firmly adhered this gelatin is to the glass and whether there are techniques that may be used locally or overall to try and begin to separate out some of these glass plate negatives. But a stack of glass plate negatives stuck one to another is not uncommon, unfortunately, and it can be very difficult to deal with. This is why, after a disaster, it's so important when things are wet to separate them, when you can, before they dry and they all stick together. Let's talk a little bit. And Angela mentioned that these are acetate negatives. Oh, these are acetate negatives. Yeah, yeah. Okay, so Angela, you're ahead of me. Well, that's good and bad, I suppose. Sometimes you can't really get acetate negatives wet. But it's the same, what's happening? It's the same issue. It's the gelatin binder, which is expanding, becoming sticky and tacky and adhering to other supports. They may, in fact, I mean, I think Angela probably knows, they could, in fact, also be salis-nitrate negatives. You see this more with salis-nitrate film. In fact, the image that you're seeing here is salis-nitrate in that gelatin becomes very deteriorated and can become quite tacky. That's part of the deterioration problem. Acetate film, the gelatin, is a little hardier. But if it gets really wet, it can become tacky. And like anything stuck together, it really needs to go to a conservator because it's so tricky to separate out these various layers. Let me, because of the time, Kristen, let me move through on nitrate and acetate, if that's okay. Sure. And see how far we get, because we're doing well, I think. And hopefully, you all can tell us if we're going to see Greta's doing a great job with your questions. And, but certainly we can slow down the pace a bit if that would be helpful. But we have a lot to cover. So salis-nitrate film. Here you see a cross-section for salis-nitrate film which is introduced or schematic, which is introduced in 1889 and popular, as I mentioned earlier, really available until 1950. But it begins to be replaced with salis-acetate film by the late 1920s and 1930s. The cross-section is a little more complex. It's no longer a one, two, or three-layered structure. You can see there's many things going on here. But basically, it's a flexible film, salis-nitrate, which is coated on one side with a gelatin emulsion. And on the other side, after about 1903 with this anti-curl layer of gelatin, that prevents the film from just rolling up like a pencil. If you have very early salis-nitrate films in your collection from 1890, for example, 1895, they may in fact be very tightly curled because they didn't have that anti-curl, anti-halation layer on the back. The subbing layer simply refers to a very thin layer that's applied to the film to try and allow that gelatin to stick to it a little bit better. And we call that the subbing layer, which is typically, in this case, might be something like salis-nitrate combined with gelatin coated on that film support. You can see in the sample in this slide some of the deterioration problems. This film is curled. It may not have an anti-curl layer. It's very brown in color. This is deterioration of the salis-nitrate base. A salis-nitrate deteriorates. It becomes more brown and deteriorated, more brittle. The gelatin also can become tacky, and the silver image begins to fade and discolor or mirror. So all these deterioration mechanisms are certainly going on in the sample that you see here. The salis-nitrate, of course, is part of this chronology that we've talked about in great detail from glass to film. It was the first flexible film support. It was light and durable, and there are many different formats for film-based materials that you may have in your collection. What was wonderful really, what was so great about this material is that it could be rolled. Suddenly, you didn't have to take one image at a time and reload the camera with another sheet of glass. Again, we take all of this with our iPhones for granted. It's hard for us to imagine. But this was a major change in the way photographs were made. And suddenly, photography was available to the market, to the masses, and to amateur photographers who could take multiple images at one time. You could, at the same time, the film is becoming faster, and you can start to capture speed, and you can enlarge. So photography is changing significantly with the introduction of silver gelatin developing outpapers and salis-nitrate film at the turn of the century. This is a wonderful image, actually, you can see from the Smithsonian. Unfortunately, salis-nitrate film does deteriorate, and in many ways that I already mentioned, but just to review it again, the base, the salis-nitrate base, becomes brittle and discolors, as you see here. The gelatin layer can become very tacky and soft and begin to stick to its enclosure. So if you have salis-nitrate films in a collection of paper-based envelopes, for example, as they deteriorate, they may become adhered to the interior of that envelope, and the silver image simultaneously begins to fade and discolor. The salis-nitrate base, as it deteriorates, is giving off many different chemicals that are actually attacking the silver image, causing it to fade and discolor. So we call this deterioration almost autocatalytic. Once it starts, it just begins to continue, and it can become very, very difficult very quickly. We often refer to the stages of deterioration when we're talking about nitrate and acetate film, and stage one with salis-nitrate film, as you can see here, is no deterioration. It's actually in very good condition, and there are many, many salis-nitrate negatives in collections that are actually in very good condition, and for that reason, they can be very difficult to identify one from another, because we often use deterioration characteristics to help in distinguishing one film from another. Stage two is, here, as you see in these examples, the negatives begin to yellow, and they begin to mirror. That mirroring, that iridescence that you see forming in the dark areas of these images is the same deterioration problem that we saw with silver gelatin developing on prints. So you'll think to see the degradation of the silver image in stage two deterioration. Stage three, now we're beginning to see that the gelatin is becoming sticky, so that gelatin layer it's beginning to stick to, it's enclosure, the silver continues to deteriorate, and you start to smell something that smells like nitric acid, so it's a strong odor that says order, and it should be odor. But anyway, it's a strong odor that you can detect and that is certainly an indication that the negatives are deteriorating. In stage four, the film is becoming much more degraded. The image continues to fade. The gelatin binder layer is tacky and the base is becoming deteriorated. It's yellowing, it's becoming brittle, as you can see in this example here. And then finally, stage five, the film base itself begins to degenerate into a brown powder. And obviously, your goal is to try and mitigate against this damage and to try and prevent this kind of deterioration. Unfortunately, a lot of it has occurred, particularly with motion picture film, as you see examples here. This is very, very common because there's a lot of cellulose nitrate in that very small canister that is closed up, that isn't breathing, and so the deterioration products that are being given off by the cellulose nitrate film are building up and attacking. It's inherently unstable. The film is deteriorated, the gelatin is deteriorating, and the image is deteriorating as well. And so your goal, of course, is to try and prevent this advanced deterioration through proper storage. We'll talk more about storage and environments at the next webinar. But it's important to mention here that the best way to preserve these materials is through cold storage. Low temperature storage in a controlled environment, controlled humidity environment, will slow down the rate of deterioration because these materials are inherently unstable. And what's challenging about cellulose nitrate film is the fact that these degradation products that are given off by the film will also attack collections, paper-based materials as well, so they really need to be separated in some way or another. But recognize that not all cellulose nitrate film is deteriorated. You don't need to immediately dispose of all your cellulose nitrate film, but you should identify it and you should segregate it. You should work towards cold storage and you should think about duplicating those materials that are readily used. It is considered a hazardous material. And you want to go back and review this slide particularly and think about some of the issues that I've listed here because you need to sort of review your fire codes, your local fire codes, your institutional insurance policies, and consult with local officials if you have cellulose nitrate film on the premise. So it may be very important in this case to hire a consultant who can work with you and look at your negative materials and begin to determine what you have and what you need to do to protect it and to protect your collection. And the National Fire Protection Association Standard number 40 is a very good document to purchase and to read carefully. And it talks about the dangers of nitrate film and the proper storage and protection of these materials. But certainly, cold storage is a priority because these low-temperature storage environments will slow down the deterioration of this material. You also want to be careful in handling cellulose nitrate film. You want to definitely use gloves because it's giving off this nitric acid. And be careful if you're wearing contacts. Be sure you're in a well-ventilated space so that there's certain health hazards associated with the handling of these materials in addition to the deterioration problems that we're speaking about. In comparison, you have cellulose nitrate film introduced in 1889. But by 1925, we begin to see the introduction of what's known as safety-based film or cellulose acetate film. Cellulose nitrate film also is flammable. And that's an important point to remember when it's very badly deteriorated. It can ignite at low temperatures. But, and this is obviously a great concern in the cause of many horrible fires in the Cleveland Clinic, a hospital in Cleveland, for example, and in motion picture film houses really throughout the country and around the world. So it was quickly replaced with cellulose acetate film base with the introduction of amateur motion picture film in 1925. And unfortunately, whereas this material is not as much of a health hazard, certainly, it too has its own set of very serious deterioration problems, which we've mentioned earlier, which is shrinkage of that cellulose acetate film base, as you see here. There's been a lot of research on acetate and nitrate film and also a lot of this done by the Image Permanence Institute. So again, I urge you to go to their website and look at the work that they've done on acetate film. A lot of this can be downloaded for free. And they're very excellent media storage guide, which you see in the slide as well, which gives you basic information on these different materials, both print and negative materials, and also recommendations for storage in terms of temperature and environmental conditions. And I will talk more about that next week. Here, I just want to introduce this material. Be sure you're familiar with it and sort of understand it. But cellulose acetate film still being manufactured, known by many as safety film. And it was introduced, again, to replace nitrate because of some of the hazards associated with nitrate film. The transition is gradual, however. So if you have collections that date to the 1930s, film-based materials, they could very well be nitrate. They may not be acetate at all. But by the 1940s, you begin to see primarily acetate film in collections. It is a generic term for very similar plastics that may be acetate butyrate or triacetate or diacetate. And it's really, in your case, not important to know that, just to know the general category of cellulose acetate. And like nitrate film, it's available in a variety of different formats. Its cross-section is very similar. To nitrate film-based, the difference is the base. And so the cellulose nitrate, now we're dealing with cellulose acetate. Again, this film, as it deteriorates, it shrinks. And you can imagine, in looking at this cross-section, that if the acetate film is shrinking, it will cause the gelatin and the anti-curl layer, which is also gelatin on the back, to appear expanded or cockled or what we call channeled. There are also plasticizers that are added to the acetate film. And they can begin to crystallize out of the film over time. You'll read about plasticizer degradation associated with these materials as well. And all kinds of formats, Fernanda gets into this in her publication. And I think you'll find it useful, because even the formats can help you from time to time in dating some of these materials. In terms of deterioration, the shrinkage bubbles and crystals refer to degradation of that plasticizer.   And it's a film-based collection. You have cellulose acetate, that's what you're smelling. And of course, your goal is to get to the point where the film isn't deteriorated. And if it's not deteriorated, you won't have that vinegar smell of acetic acid, which is the degradation of that cellulose acetate polymer as it begins to deteriorate over time. Unlike the cellulose nitrate image, one piece of good news here is that the silver images in cellulose acetate film do not fade and discolor. Acetic acid is what's known as a mild acid, a weak acid. And it's not strong enough to attack silver images. And so these images appear to be in relatively good condition. Unfortunately, the base, of course, has deteriorated. And here's another example of an image that's beginning to channel and distort. Like the cellulose nitrate film, we talk about stages of deterioration with cellulose acetate film as well. And you can see them here in this particular image. And I think, I'm checking to see, I may have even more images to show you. But what you're seeing here is sort of the very stages of deterioration of cellulose acetate film. The first film at the far left appears to be pretty flat and not very distorted. The image is in relatively good condition. But you can see in the next negative that it's a little bit more curled. It's beginning to lift at the edges. That's through the second stage of deterioration. And as it progresses, you can see that the acetate is shrinking more and more. And the channeling is much more progressive. You begin to see more crystals form. Again, the silver image doesn't deteriorate. And again, in this image, you see that blue dye, the anti-halation dye, which is regenerated. And visible. But this degradation, like cellulose nitrate film, is accelerated by exposure to poor environmental conditions. And it can happen relatively quickly. There's a lot of very important research that's been done by the Image Permanence Institute at the Library of Congress, the National Archives, the other organizations and institutes and research institutes really around the world looking at cellulose acetate film degradation. And beginning to track the relationship between time and acidity level. And in this diagram, you can see that there's a certain point where degradation begins to increase at almost a catastrophic speed. And it's important in trying to determine where your collection is on this chart. Ideally, your collection is still in relatively good condition. And you can house it in a good environment and prevent that sort of catastrophic channeling.  And they allow you to begin to determine when a cellulose acetate film has begun to deteriorate. Before, you can see something that's visually apparent. It's a color, it's a pH detecting paper. And I don't have time to go into how to use them, but suffice it to understand that they are available to you. And if you have a motion picture collection or a collection of acetate films and paper enclosures that are still in relatively good condition, you want to begin to determine their extent of deterioration and where they are on that graph. You can buy these AD detector strips, follow the directions, and monitor the color change, which happens pretty immediately. You can see it here compared to this pencil. And begin to predict the life expectancy of your collection and also what's most important, the environment in which it must be housed to preserve it, which is typically a low temperature, low relative humidity environment. But these AD strips are incredibly useful for better understanding the mechanism of the deterioration problems associated with acetate film. I want to be sure that you are aware of them. Finally, I've got a whole other section, but I'm going to take up a break for a few questions in a minute. But I also wanted to mention that in 1951, we see the introduction of polyester film. So polyester film, which is very, very stable, that's the good news in all this excellent stability. Stable doesn't even require cold storage for its long-term stability. It's introduced in 1951 and still used with many photographic processes today. It has both high chemical and physical stability, and it's used in a variety of formats. So you have sort of an evolution from cellulose nitrate to cellulose acetate to polyester film, which is used today. Let me just say a few words about identification and then I can take some questions. And that is just to say that, again, there's some excellent information available for all of you on the web. This is something from the Northeast Document Conservation Center, which is a leaflet on the identification of film-based materials written by Andrew Robin, Monique Fisher. And it begins to distinguish the different materials and how to identify them using different dates and then different deterioration mechanisms. Similarly, the National Park Service has developed a whole nother scheme. This is hard to see. You really have to go online. I did it as a screenshot, but I can't even read it on my screen at this point. But it's another flowchart. It's another system for identifying one film from another. This is interesting because it just asks you a series of questions. Is it this or is it that? And it can help you begin to determine do you have acetate nitrate or polyester film. Certainly dating will help you, as is true with albumin versus silver gelatin, developing out papers. Images from 1889 to 1925 on film are likely to be silo nitrate. From 1935 to 1960 may more likely be silo acetate. So dating is something to consider. And in some of the negatives, you'll also see that they're printed on the outer edge. So they might actually say nitrate or safety film. And certainly that can help you in differentiating one process for another. There's also all kinds of references for motion picture film and sheet film notch codes. And sometimes the notch codes that you see in these materials will refer back to not only dates, but also film type. So edge printing can be useful. Deterioration is really your best bet. And if I had you all in a room and I could see all your faces, I would ask you to raise your hands. We should have done a poll. Kristen, we need to do that. I'll do a few questions next week. What is this? Is it nitrate or is it acetate? This is a little bit complicated, really. And of course, I told you in the label, so it's clear. But this is acetate film. It's channeling and deteriorating. But what's confusing a bit about this is most acetate film does not become brown or discolored. As you see here, this one is definitely deteriorated in ways that's somewhat uncommon. But that channeling and that deterioration that you're seeing, the cockling or the wrinkling, is very characteristic of acetate film. So deterioration will certainly be something to consider. Finally, we'll talk about storage. But I wanted to be sure that you're aware of the fact that the National Park Service has done some very significant work on cold storage and created all kinds of videos and online information about the storage of these materials or the proper storage of these materials using cold storage, how to differentiate them, and how to house them properly. And this is a wonderful online resource with films and information that I think will be very helpful to you as you review some of the information that we covered in the webinar today. Fundamentally, you always need to think about these materials and the importance of preserving them, because the negative is often considered what's most important in these collections. There's only one negative from which many prints may be made. And a lot of these negatives are very important, artifactual value. They were made by Ansel Adams. They were made by Gertrude Casabere. They were made by Walker Evans. And they reveal a lot about the artist intent about the photographer's working properties. And so the preservation of these materials, despite their many challenges, is critical and something that can be difficult because of the numbers and their inherent instability. We begin to see degradation problems with negatives that you really don't see with photographic print materials. So with that, let me turn this over to Kristen and see what questions have emerged. One thing I'm finding, I wish, again, I could show you all my screen. I can see you're asking lots of questions. I can see that Greta is answering them as quickly as she can. But I'm trying not to follow the question so I can focus on what I'm saying. So now, Kristen, let me know what questions I might be able to help with. OK. Well, I just wanted you, when you talk about nitrate, you are getting, you kind of walk into the motion picture part of the field. And so I just wanted to also remind people that we are planning a care of audio-visual materials course for next fall. So stay tuned for that where we can get into more depth. But it just seems like a couple of questions are coming in about cellulose nitrate items, negatives, versus, let's say, a whole role of film and would the danger or hazards be greater because of the greater volume in a canister of film versus a single negative. OK. And then what do you mean by separate those out? OK. I just put on, not the final slide, but almost the final slide, which was another, I hope you all are able to go back to these slides. I know you can and to gather these websites. But here's more information on motion picture film as it relates to dates and popularity, deterioration problems, et cetera. Certainly, a lot of the research on cellulose nitrate film has been focused on motion picture film, given its value and its importance. But it is true that in terms of health and safety issues and flammability and degradation problems, the motion picture film is more challenging simply because there's just so much more film in that closed canister. Whereas when you have a collection of film-based sheet film, for example, in paper enclosures, there's not as much film. It still will deteriorate in many of the same ways, but it won't deteriorate quite as quickly just because of the bulk of the film. All of that film will together tightly in a closed container. This deterioration is autocatalytic. Again, it builds on itself. So as it deteriorates, and it's in a closed environment and not able to breathe, it deteriorates more quickly and more rapidly. When you have a collection of sheet film housed in paper enclosures, there's more air circulation. There's a little bit more breathability, and the degradation rate may be slower. But a lot of that has to do with the environment, too. You take that collection, you put it in the attic. It's going to deteriorate pretty quickly, and it could become quite a challenge. In terms of separating, what do I mean by that? Well, a few different things. One is, if you have salis nitrate materials in your collection, you have to just recognize that the salis nitrate film is not only deteriorating, but it's giving off nitrous oxides and nitric acid that can attack adjacent collection materials. And even causing the shelving, the cabinet tree, the stainless steel shelving to rust and deteriorate. And so it's important to begin to separate out those materials and house them in the best possible environment that you have available to you, but not adjacent to other collection materials. The exception is, if you can possibly move towards cold storage, you then would simply separate out all your film-based materials, acetate and nitrate. Not necessary to distinguish nitrate from acetate, but just take all the film material and put that into cold storage or cool storage. And then separation is not such a critical problem. It's all compounded. It's really difficult. And this could be the focus of an entire webinar with individuals who have enormous expertise in this area.  All of those issues have to be investigated. And you can bring a consultant in who could work with you and also consulting with the local fire protection fire department even to talk about these materials. They need to be aware that you have them on the premise. And the other final thought that I will leave you with is that as these materials deteriorate, they become more dangerous, more problematic. So, stainless nitrate in good condition is not certainly as much of a problem as that nitrate film that's very badly deteriorated in stage five deterioration. That's much more difficult and much more problematic. Does that help? Yes, it does. And those references that you provided today throughout the IPI media storage guide and they're all linked on our website. And there's really been great information sharing about this issue and written in very approachable ways. So, just encourage people to check out the sites that Debbie mentioned because there's a lot of good information very accessible to us now. Yeah, I think that this is one wonderful thing about the field of photograph conservation. I can say so. Because there's photographs all over the world and we're well aware of that and we're working where we can to preserve these materials around the world. But we've recognized, the field has recognized how vitally important it is to make this information accessible, understandable, basic, and to be well aware of the challenges that each of you face. There are the ideal solutions to all of these preservation issues, but it's important that we focus on realities and practical solutions. And you'll find in many of these resources excellent practical recommendations for short and long term preservation. Right, I know I'm seeing some questions about hold storage and freezer storage and that there's the National Park Service resource you mentioned is really, really very good and very approachable about that too and gets into all the specifics you'll need. And we also on the Connecting to Collections online community had a webinar just on that topic. And I was very, this is very simplistic, but your basic appliance, store, freezer, or refrigerator can sometimes solve an issue for you. So we walk you through all those steps. So it can be very, very approachable for any type of institution, any size of institution. So there was another conversation going about the stickiness as part of the deterioration that you talked about. And people had heard about the term sticky shed in terms of film, but not necessarily a thing. That's not really a sticky shed. I don't want to get out of my league. OK. I'm sure there's some insufficiency in our mind. So you just want to clarify that point. Yeah. Yeah, but that does to do more with magnetic media. OK, OK. It is a term that's used, but we don't necessarily use it with photographic material. So the stickiness that we're talking about with photographic materials is primarily deterioration of that gelatin binder layer. Again, gelatin is a commercially prepared protein as well upon exposure to moisture, and it can become very tacky. And that is a deterioration that occurs following a disaster when materials get wet, when they're stuck together. And with Silo's nitrate film, as that base deteriorates, it attacks the gelatin, causing it to become tacky and sticky. OK. But it is separate from sticky shed. For that term, sticky shed. Yeah, in terms of terminology, and someone online, I'm sure it can address that far better than I can. OK. And then although conservators may have some methods to reverse or stabilize something that's become sticky, that's not something you would do without the help of a conservator. So I think that had to reflux the conversation. I mean, I think another important message there is just when these things all have become adhered and sticky and deteriorated. Some institutions just immediately start throwing all these materials away. And I would just urge you not to do that, to bring in a consultant to see what can be saved. Because there are techniques, not in all cases. In some cases, unfortunately, nothing can be done. But there are techniques to at least preserve the image or try and preserve the object. But it is a difficult problem. And it's very different from Silo's acetate film. And Silo's acetate film deteriorates, although one of the participants mentioned about acetate film sticking together, that can happen. But for the most part, the gelatin is actually in relatively good condition. It is deterioration of the base, the shrinkage of the base, deterioration of the plasticizer that's causing more planar distortion, physical distortion, as opposed to chemical distortion of the gelatin. Right. And then that's where the cold storage comes into play. Because then that deterioration will be radically flowed when, so again, I'm looking now for my link for that webinar. But because it depends on the material and then how you wrap it to put it into cold storage is very important, too. Yeah. And actually, the other thing I'm looking at, it looks like one of our participants creating a database of all the links. And that would be really a great thing. Well, it's on our site. But I think, yeah, it's going to say, I thought they can go online and they all link already, right? It's all linked there. And all the great resources you discovered and have put on, or you've told us about and put on the course web page will be under our topics menu in Connecting to Collections dot org. So of course, obviously, if it's easier for a person to create their own personal database and keep it handy, that's great. But just always remember that we're constantly improving filing links like this so that we've done the work for you and just can be a ready resource. As you all, we only have two more of these left. And we'll try and answer as many of these questions as we can. But again, I just urge you to send images of problems because I'll try and do the same thing. I'll try and start next webinar with some of the images that we receive as a review of what we've discussed. But hopefully also pinpointing some of the questions that you have about your own collection. Okay. I mean, we can get one more question before you have to go, but I just wanted to tell everyone about the homework. It's going to be similar to last week's homework. Or just if you can identify a negative in either your institutional collection or your personal collection, give some more indication of what kind of negatives you have and then what would be some concerns you have and why. And I'll put the link here. And if you have attended with a colleague today, please let us know who they are so we can give them credit for attending. If you attended by yourself, don't worry. You know who you are. We saw you log in. So let's see if I have another question over here. Greta's doing, Greta, you're doing a great job. By the way, everyone out there, I had mentioned that when Heather was on, this was part of her exam, but Greta also will be finishing up her study and receiving her Master's of Science in August. And this also exercises for the part of all that too, and it seems that both Heather and Greta have just done a fantastic job in addressing a lot of questions in a very succinct way. So I thank you, Greta, for being online. Right. So, and I saw Cindy doesn't have a negative. Any negatives? If there's some, you know, I would, you know, do something you have at home, maybe, just anything in your personal collection, could be fine or someone you know, family member, could help them out with some of their... Yeah, and Cindy, if not, maybe you could just, you know, just tell us that and do another. Look at your photographic prints again or photographic albums. Yeah. We don't wanna create work that's not gonna help you, but most institutions have negative. It's interesting. I mean, from Fine Art Museums to Historic Houses, and they are a challenge because there are many of them. Great. Okay, well, if I have missed someone's question and Greta didn't get to it today, we always send a summary over to Debbie and we'll do our best to leave it into the future webinars, but I want to thank everyone again for their time and attention today, and again, we will meet next Tuesday at one o'clock for another webinar, and getting a little bit more into the preventive conservation aspect of this series. So thank you again for your time and thank you, Debbie, for all this great information. Oh, it's my pleasure. It's a lot of fun. I just wish I could see everyone, but I'm enjoying it. Thank you, Kristen and Jenny, Greta, Mike, on for all your support. And we'll see you all next week, Tuesday, one o'clock Eastern Standard Time. Excellent. Thanks for having a great day.