The Light Farm, Volume 2, Beyond Basics (under construction)


The following vocabulary words and concepts will get you started working and understanding the recipes and literature. Reading from the Light Farm literature list will rapidly pad your comfort zone. The vobulary chapter in 'The Light Farm, Volume 1, The Basics' is far more extensive and is suggested reading.

There is a key concept here: learning is a positive feedback loop. You will not know how to make emulsions until you start making emulsions. With each lap around the circle you will understand a couple more ideas and procedures. The great gobs of words written by T. Thorne Baker, for example, will actually start first to make sense, and then to sound like poetry as the cadence of slightly archaic style weaves through your experience. Vocabulary is more than words. It is also tactile knowledge. A person may be able to read musical notes on a page without knowing how to play an instrument. A musician — with rare exception — knows both.

(Links to examples, where appropriate, will be part of the final form of this page.)

Bloom (verb)
In a recipe it means to swell gelatin in water (soaking long enough for complete rehydration).

Shorthand for baryta-coated paper, today usually glossy. Plain, glossy commercial baryta paper gives the smoothest surface for coating. A high gloss, perfectly smooth surface is impossible to achieve without a "calendering" machine — a great beast not suitable to d.i.y. The texture of handmade baryta paper has a bit of tooth, but still gives a smoother coating surface than uncoated HP (Hot Press/smooth) watercolor paper, and is much less porous.

Bloom number
A measure of the hardness of the gelatin. Emulsion makers generally use 250 bloom (hard/photographic gelatin). A lower number is softer; a higher number is harder. 300 bloom gelatin dries to a degree of hardness that is very brittle rather than flexible.

Contact Printing
Making a print from a film negative or dry plate by shining light through a negative that is in direct contact with printing paper. The resulting print is identical in size to the negative. This is in contrast to "enlarging" which makes a print larger than the original negative. Contact printing requires only a light bulb and a contact printing frame. Enlarging requires an enlarger with a lens, and normally a printing eisel.

See "Emulsion Making Stages"

Dry plate (or gelatin dry plate)
Silver gelatin negative emulsion coated on glass, dried before storage and exposure. Same as 'glass negative' (as opposed to 'wet plate', which is collodion rather than a gelatin-based process).

Photographically, melted gelatin and one or more silver halides, along with any number of other specialized additions, coated and dried onto paper, glass, or film.

Emulsion Making Stages

Emulsification (also called Precipitation)
The first and main reaction of silver halide formation (the addition of silver nitrate to at least one salt). This step determines in large part the characteristics of the final emulsion. The gelatin used during the Precipitation step is quite naturally called the precipitation gelatin. In general, the less used, the larger the grains produced, and the faster the emulsion — again, a generalization. Most negative emulsions aim for the minimum gelatin necessary to keep the silver halides in suspension during the process. Some gelatin is necessary to keep the silver and the halide from forming big clumps that sink like worthless rocks.

Ripening (also called Physical Ripening or First Ripening)
This step determines whether the emulsion will be a fine-grained slow emulsion or a larger grained faster one. You will sometimes see the entire step referred to as Ostwald ripening, although this is technically a subset process of ripening.

Second Gelatin (also called Make-Up Gelatin)
Gelatin that is added after precipitation to bring the viscosity of the emulsion up to coating weight. More gelatin can be added after the noodle washing step. This gelatin is most commonly called make-up gelatin.

Washing (also called Noodle Washing)
In washed emulsions, breaking the ripened, chilled emulsion into little pieces ('noodles', 'shreds', or 'worms') to facilitate washing out ammonia (if used) and excess salts that could re-crystallize on film or a plate. The washing step is not required when for paper emulsions made without ammonia.

Digestion (also called Chemical Ripening, Second Ripening, or After-ripening)
At this point various additives are inserted primarily for influencing sensitivity — color sensitivity or over all sensitivity to light (i.e., "speed"). (For instance, additives are necessary to make a film orthochromatic or panchromatic (i.e., sensitive to the full visible spectrum. Silver halides are naturally sensitive to only UV and blue-violet light.)

Emulsion vs. Colloid
By convention, the mixture of a silver halide and gelatin is called an emulsion even though it is technically a colloid — a dispersion of microscopic particles that do not fall out of suspension. Another use of the word 'emulsion' is to refer to a particular film, even though technically most modern films are a mixture of more than one emulsion type. For our purposes — coating an individual emulsion on paper, glass, or film — 'emulsion' is correct usage. But, as with all slang and jargon, the technicalities of correctness are not hairs worth splitting when weighed against history and habit.

High proof ethanol alcohol and for all intents and purposes indispensable for emulsion work. Although 'Everclear' is a brand name, it is also the generic reference to similar alcohols. In Oregon the brand is 'Clear Spring'. 'Everclear' is illegal in a number of states, but worth the drive to find. It is also available online.

Any of the many ingredients that can be added to an emulsions immediately before coating — most often surfactants and hardeners.

On glass negatives, the emulsion lifting or floating away, usually from the edges of the plate, but also starting as bubbles anywhere on the plate. A little edge frilling will not ruin an image. The best prevention is keeping the temperatures of developer, stop, fix, and washing water all the same and around 65°F/18°C, and handling the plates gently at all times. If need be, a hardening fix can be used.

Gaslight paper
Any of a variety of very slow papers, usually AgCl. The name comes from the fact that the paper didn't require a darkroom. It could be worked in the light of a low-burning gaslight. Today, that implies a bright amber safelight, although any paper should be tested for light sensitivity, Because of their relative insensitivity (i.e., slow speed) gaslight papers are by definition contact printing papers.

The stuff that miracles are made of. Modern photographic gelatin is generally "inactive" — as close as possible to being a neutral base. "Active" gelatin is any gelatin, including food gelatin, that has not been deliberately made inactive/neutral. Using active gelatin introduces many unknowns into the system. Given the price of silver nitrate, using a known product like high-quality photographic gelatin is a very smart use of money. Photographic gelatin is usually 250 bloom, or "hard" —"hard" means just what it sounds like. Back in the day, emulsion makers used both hard and soft gelatins at different points in the making process. There may have been more art than science to this practice. At any rate, it is not something TLF recipes pursue. Active gelatins were also rated by their impurities that affected emulsion making. That rating system was different from the "hard-to-soft" classifications. Today, using inactive gelatins and separate additional chemicals, we can control the influences on emulsion quality and character.

An organic compound, in liquid form, which can be used to harden emulsions emulsion coated on paper.

Halation and Antihalation layer
During exposure of film or glass plates, light passes through the emulsion and bounces off the substrate and back again through the emulsion. This can cause halos to form around objects => halation. Modern films have a layer that prevents the light bounce-back and eliminates halation => antihalation.

The measure of acidity (pH below 7) vs. alkalinity (pH above 7). Distilled water is the neutral baseline at 7. The "H" refers the hydrogen ion. Sometimes pH is written as p[H]. There is little reason to measure pH in the normal course of things, but inexpensive meters and/or "litmus" paper are readily available from science supply stores. pAg (and the related vAg) is the silver equivalent of the concept of pH. It refers to the concentration of silver dissolved in solution. It cannot be measured with a pH meter. Although it can be a useful measurement in complex commercial emulsion making, it is of little value to us, except for those folks who enjoy making d.i.y. lab equipment.

The post-exposure stages of develop, stop, fix, and wash. Fix used to be commonly called 'hypo'. From there, the optional step of 'hypo-clear' was named. Hypo clear and Fix are altogether different steps. Hypo-clear has various names, including Hypo-Wash, Orbit Bath, Archival Wash Agent, etc. It comes between the fix step and washing and is far more useful with paper than with film. Its use reduces wash time and conserves water, but the directions must be followed closely. With film, the last step is a wetting agent, commonly Kodak Photo-Flo or its equivalent in different brands.

See "Emulsion Making Stages"

The step of adding one or more extra chemicals to the emulsion to enhance the basic properties of the silver halides. This can mean speed and/or parts of the spectrum beyond UV and blue-violet. Gold and sulfur can be added to increase the speed (e.g. Steigmann's Solution). Various dyes can be added to make the emulsion orthochromatic, panchromatic, or IR (infra-red).

Silver Halides
Light sensitive compounds of silver formed during emulsion making: silver chloride (AgCl), silver bromide (AgBr) and silver iodide (AgI), often designated generically as AgX. There are any number of chemicals that can contribute the Cl, Br, or I parts of a silver halide. The 'Ag' part is always from silver nitrate (AgNO3).

The term for how 'fast' or 'slow' an emulsion is. In modern usage this is noted by the ASA or ISO numbers. In reality, speed is not an absolute. The actual sensitivity to light of any emulsion, and most certainly handmade ones, varies with time of day, time of year, and weather conditions. It is also influenced by developer choice. Experimentation, with careful and consistent note taking, is the time-honored method of determining the actual working sensitivities of your film. ASA/ISO numbers are only the starting point.

"Subbed" (film)
From 'substrate'; film base that has been coated with material that helps the emulsion adhere through the various processing steps.

Wetting agent. I use Photoflo and/or Everclear (ethanol).

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