10.6092/issn.1973-9494/12791
Albumine, gelatine d'argento e stampe cromogeniche si trovano in abbondanza nelle collezioni fotografiche in Egitto. A causa dell'ambiente non controllato negli archivi e nelle biblioteche, questo prezioso patrimonio visivo con il suo alto contenuto di proteine ​​e cellulosa fornisce il terreno di coltura per la crescita dei funghi. Molti oli essenziali hanno dimostrato di avere proprietà antibatteriche e antimicotiche. Gli oli essenziali offrono un'alternativa sicura ad altri metodi di disinfezione comuni; tuttavia, non ci sono molti studi sul loro effetto sulle proprietà delle fotografie. Questo articolo descrive l'effetto dei vapori di oli di anice, cannella, chiodi di garofano, lavanda e timo su albumine, gelatina d'argento e stampe cromogeniche, per trovare un metodo di disinfezione adeguato che sia facile da usare e sicuro per l'ambiente nel rispetto dei materiali fotografici. Gli oli essenziali sono stati forniti dal National Research Center (NRC) deI Cairo, in Egitto. Stampe all'albume invecchiate artificialmente, gelatine d'argento invecchiate naturalmente e stampe cromogeniche sono state esposte in essiccatori agli oli essenziali selezionati in fase vapore per un periodo di 5 giorni. Tutti i campioni sono stati invecchiati artificialmente a una temperatura di 80 °C e 65% di umidità relativa per un periodo di 5 giorni per studiare gli effetti a lungo termine dei trattamenti testati. I trattamenti sono stati valutati utilizzando diverse tecniche, tra le quali ispezione visiva, ispezione microscopica, misurazioni colorimetriche e spettroscopia a infrarossi in trasformata di Fourier a riflettanza totale attenuata. I risultati hanno mostrato che tutti gli oli essenziali testati hanno avuto un lieve effetto sui campioni fotografici testati; l'olio di lavanda è risultato essere l'opzione migliore, in particolare, in termini di salvaguardia delle proprietà chimiche delle superfici fotografiche.
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Conservation Science in Cultural Heritage
ATR-FTIR
Effect of Five Essential Oils as Green Disinfectants on Selected Photographic Prints: Experimental Study 
Text.Serial.Journal
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Articles
2021-05-13
2021-04-27
2021-05-13
2021-05-13
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Maha Ali
2020
10.6092/issn.1973-9494/12791
79
Faculty of Archaeology, Cairo University, Egypt 
1973-9494
ATR-FTIR
en
97
Effect of Five Essential Oils as Green Disinfectants on Selected Photographic Prints: Experimental Study 
https://conservation-science.unibo.it/article/download/12791/12507
20
E    FFECT OF FIVE ESSENTIAL OILS AS GREEN
     DISINFECTANTS ON SELECTED PHOTOGRAPHIC
     PRINTS: EXPERIMENTAL STUDY


   Maha Ali *
   Faculty of Archaeology, Cairo University, Egypt


   Keywords: fungal damage, essential oils, colorimetric measurements, ATR-FTIR




   1. Introduction

    Old photographs found in private collections, archives, fine art collections, or mu-
seums are rich and valuable resources that visually document information on individu-
als, social groups, places and events that have shaped our history [1]. Photographic
heritage is now recognized as having a key role in the documentation and conserva-
tion of cultural heritage [2]. Preservation of these precious records significantly contrib-
utes to giving us a sense of identity, responsibility and continuity [3]. Nevertheless, pho-
tographic materials do present special challenges to conservators due to their complex
nature which varies from one photographic process to another [4, 5].
    Photographic images exist in many forms around the world, ranging from rare prints
and glass negatives to photo albums, 35mm slides and color prints [6]. Albumen, silver
gelatin and chromogenic prints are by far the most common positive printing photo-
graphic processes existent among photographic collections in Egypt. The albumen pro-
cess invented by French photographer Louis-Désiré Blanquart-Evrard in 1850 was the
dominant positive monochromatic printing photographic process of the 19th century [7].
Blanquart-Evrard published a total of 24 albums which were thoroughly investigated by
Isabelle Jammes in Blanquart-Evrard et Les Origines de L’édition Photographique
Française: Catalogue Raisonné des Albums Photographiques Edités [8]. Albumen prints
were commonly used as book illustrations from 1855 to 1858, resulting in numerous
albums providing biographical, historical, scientific and topographical images that fea-
tured sharp definition, a glossy surface and strong contrast as mentioned by Naomi
Rosenblum in A World History of Photography [9]. Albumen prints are composed of two
layers: the primary support (i.e. a thin smooth sheet of rag paper) and the albumen
binder layer (i.e. egg white) carrying the final image material (i.e. toned photolytic silver
particles) [10]. In the 20th century, the silver gelatin process was the main positive mono-
chromatic printing photographic process. Basically, a silver gelatin print is composed of
three layers: the primary support (i.e. paper), the baryta layer (i.e. fine particles of barium
sulfate in a gelatin layer) and the gelatin binder layer, which carries the final image
material (i.e. filamentary silver particles) [11-13]. As for chromogenic prints, they were
the classic form of color photography in the latter half of the 20th century. Chromogenic


   * Corresponding author: maha.ahmed@hotmail.com
                                                                                                                    prints are composed of yellow, magenta and cyan organic dyes distributed in three
                                                                                                                    superimposed layers of gelatin (i.e. the binder). These three binder layers are supported
                                                                                                                    on a paper support coated with baryta [14, 15]. Silver gelatin prints and chromogenic
                                                                                                                    prints were also supported on resin-coated paper supports. The paper base of this type
                                                                                                                    of support is coated on both sides with a thin layer of polyethylene. A white pigment,
                                                                                                                    usually titanium dioxide, is added to the polyethylene layer on the binder side of the
                                                                                                                    print [16]. In general, all three types of photographs are considered composite objects;
                                                                                                                    however, chromogenic prints are much more complex in structure than monochro-
M. Ali - Effect of five essential oils as green disinfectants on selected photographic prints: experimental study




                                                                                                                    matic prints [17]. With regard to historical and technical background on the previous
                                                                                                                    photographic processes, detailed studies are provided by Robert Hirsch in Seizing the
                                                                                                                    Light: A Social & Aesthetic History of Photography [18].
                                                                                                                         Photographs preserved in libraries, archives and museums are subject to deteriora-
                                                                                                                    tion caused by physical, chemical and biological agents [19, 20]. For photographic col-
                                                                                                                    lections, fungal development is a recurring problem and is therefore considered a major
                                                                                                                    cause of deterioration [21]. Depending on their geographical location and weather con-
                                                                                                                    ditions, archives and libraries contain more fungi compared to other enclosed spaces
                                                                                                                    [22]. These microorganisms play a substantial role in the deterioration of most photo-
                                                                                                                    graphs due to their enormous enzymatic activity and their ability to grow at low values of
                                                                                                                    water activity [23]. Photographic binders with their high protein content, and paper sup-
                                                                                                                    ports with their high cellulose content, provide the culture medium required for fungal
                                                                                                                    growth [24]. The high water content and hygroscopic nature of photograph components
                                                                                                                    make them more susceptible to damage by fungi [14, 25, 26]. For many types of fungal
                                                                                                                    growth, the optimum environment is over 22°C and over 70% relative humidity with poor
                                                                                                                    air circulation [27]. When an appropriate combination of nutrients and environmental
                                                                                                                    conditions are present, spores absorb water and grow rapidly, branching out repeatedly
                                                                                                                    to form a colony [14]. The most representative fungal species found in photographic col-
                                                                                                                    lections belong to the Aspergillus, Penicilluim, Mucor, Cladosporium, Trichoderma, and
                                                                                                                    Phoma Species [28]. A. ustus, A. nidulans, A. versicolor, seven Penicillium chrysoge-
                                                                                                                    num strains, A. alternata, C. cladosporioides, Mucor racemosus, Phoma glomerata, and
                                                                                                                    Trichoderma longibrachiatum were isolated from selected samples of cinematographic
                                                                                                                    films collected from archives around Spain [29]. Fusarium, Humicola, Paecilomyces,
                                                                                                                    Trichoderma and Ulocladium species were isolated from art photographs that were tem-
                                                                                                                    porarily stored at the Cultural Center of Belgrade [30]. Microbiological studies conducted
                                                                                                                    in two repositories of the National Archive of the Republic of Cuba on silver gelatin
                                                                                                                    prints, albumen prints, collodion prints and dry glass plates, identified Aspergillus and
                                                                                                                    Penicillium as the predominant genera. Other genera, including Emiricella, Eurotium,
                                                                                                                    Cladosporium, Talaromyces, Candida and Rhodotorula were also detected [22].
                                                                                                                         Damage caused by fungi can be extremely devastating since they are capable of
                                                                                                                    mechanically, chemically and aesthetically damaging photographs [31]. Fungal hyphae
                                                                                                                    can burrow extensively, forming a network of tunnels below the binder surface [32].
                                                                                                                    Fungi can also produce chromatic alterations such as stains of various colors due to
                                                                                                                    mycelium growth and the release of colored metabolites [33]. They feed on the organic
                                                                                                                    components of photographs by extracting carbon and nitrogen through an enzyme
                                                                                                                    hydrolysis reaction that weakens and lowers their mechanical strength [20]. They can
                                                                                                                    produce hydrolytic enzymes such as cellulase, xylanase, pectinase, etc. [34, 35]. The
                                                                                                                    photographic binder is more hygroscopic than paper and its proteinous nature makes
                                                                                                                    it highly receptive to fungi [36]. Binder degradation by fungal growth is a serious problem
                                                                                                                    since it causes the loss of the image [37].


                                                                                               80
    Different disinfection methods can be used to prevent and/or stop the biodeteriora-
tion caused by fungi in paper-based objects. These methods include controlling the
surrounding environmental conditions, using biocides, application of heat or radiation,
and plasma [38, 39]. Installing an efficient climate control system can either be too
costly or too complicated [40, 41]. Fungicides have been widely used to disinfect con-
taminated paper such as thymol [42], ethyl alcohol [24, 43, 44], ethylene oxides [45-47],
formaldehyde [48] and many others. However, the use of chemical disinfection meth-
ods is becoming increasingly restricted mainly due to their damaging effect on the en-
vironment and human health [49, 50]. Moreover, they are known to cause damage to
paper collections; for example, thymol causes changes in the physical-chemical char-
acteristics of paper, as well as the yellowing of prints sealed in frames [38]; radiation
causes the deterioration of paper [39]. These factors have forced researchers to search
for other safe and natural alternatives.
    The use of essential oils in the conservation field has received great attention in
recent years due to their antibacterial and antifungal properties [51]. Essential oils are a
mixture of volatile aromatic concentrated hydrophobic oily liquids which are extracted
from various plant parts [52, 53]. Many publications have discussed the successful use
of essential oils (i.e. Artemisia, boldo, eucalyptus, Ravensara aromatica, lavender, tea tree,
Thuja, clove, wormseed, anise, cumin, garlic, laurel, sweet orange, oregano, thyme, cin-
namon, and others) in controlling the biodeterioration of documentary heritage, focus-
ing mainly on paper [39, 40, 51, 54, 55]. One study evaluated the effect of linalool, a
compound found in essential oils, on silver gelatin prints and it was found to be damag-
ing [41]. On this basis, the aim of this research was to assess the effect of five selected
essential oils in vapor phase on the optical and chemical properties of common photo-
graphic materials found in Egypt in search of a disinfection method that is user-friendly,
environment-friendly and safe to use with the selected photographic materials.




                                                                                                      Conservation science in Cultural Heritage
   2. Materials and methods

   2.1. Test materials

     For this experiment, 10 naturally aged silver gelatin (DOP) and chromogenic prints,
five of each type, were selected as samples in order to give a more practical, rather
than theoretical focus to this study. Five albumen prints were also used as test sam-
ples; however due to lack of antique prints, the sample set used in this study was
prepared in the Photography Laboratory at the Faculty of Archaeology, Cairo Univer-
sity following the steps of the original process [56, 57]. The albumen prints were artifi-
cially aged at 80°C and 65% RH for 5 days, which is equivalent to the aging of paper
under natural conditions for 25 years. The aging procedure was in accordance with
ISO 5630-3:1996 standard [58, 59]. This process was performed in a BINDER drying
oven with digital indicator, model no. 92403000002000 at the National Institute of Stan-
dards (NIS) in Cairo, Egypt (Figure 1).
     Mylar templates were made to mark the precise area on each photographic print to
investigate and measure, using a digital microscope, spectrophotometer and FTIR spec-
trometer, before exposure to essential oil vapors and after exposure and artificial aging
(i.e. accelerated aging). Investigations and measurements were done on two areas of
each sample; one Dmin which was given the number 1 and another Dmax which was
given the number 2 (Figure 2).


                                                                                                 81
M. Ali - Effect of five essential oils as green disinfectants on selected photographic prints: experimental study




                                                                                                                    Figure 1. Test samples. (A) Artificially aged albumen prints; (B) naturally aged developed-out
                                                                                                                    silver gelatin prints; and (C) naturally aged chromogenic prints.




                                                                                                                    Figure 2. Mylar templates for anise oil sample set. (A) Artificially aged albumen print; (B) natu-
                                                                                                                    rally aged developed-out silver gelatin print; and (C) naturally aged chromogenic print.


                                                                                                                        Photographic samples were numbered on the reverse using a graphite pencil ac-
                                                                                                                    cording to the photographic process used (i.e. A for albumen prints, B for silver gelatin
                                                                                                                    prints and C for chromogenic prints) and the type of essential oil to be tested (i.e. A for
                                                                                                                    anise, CL for clove, L for lavender, C for cinnamon and T for thyme) as shown in Table 1.

                                                                                                                    Table 1. Labelling of print samples according to the tested essential oil

                                                                                                                                                   Albumen prints      Silver gelatin prints    Chromogenic prints
                                                                                                                     Anise oil sample set                 AA                    BA                     CA
                                                                                                                     Cinnamon oil sample set              AC                    BC                     CC
                                                                                                                     Clove oil sample set                ACL                   BCL                     CCL
                                                                                                                     Lavender oil sample set              AL                    BL                     CL
                                                                                                                     Thyme oil sample set                 AT                    BT                     CT



                                                                                                                        2.2. Essential oils

                                                                                                                       The following five essential oils were selected owing to their antibacterial and anti-
                                                                                                                    fungal properties as mentioned earlier: lavender, clove, anise, cinnamon and thyme, all


                                                                                                    82
of which were extracted using the cold press method. The essential oils were provid-
ed by the National Research Center (NRC) in Cairo, Egypt.


   2.3. Application method

    Samples were exposed to selected essential oils in vapor phase to avoid direct
contact of the oils with the photographic surfaces which would undoubtedly lead to
severe staining. Five glass test-chambers (i.e. desiccators) were used, one for each
selected essential oil. 25 ml of each oil was poured into a glass beaker and placed in
a desiccator. A petri dish with saturated magnesium sulfate solution was placed in each
desiccator to maintain humidity at 80%. Each desiccator contained an albumen print,
a silver gelatin print and a chromogenic print. Samples were exposed to the vapors of
the oils for a period of 5 days (Figure 3).


   2.4. Artificial aging

    The samples went through accelerated aging post exposure to evaluate the long-
term effects of tested oils on the optical and chemical properties of photographic sam-
ples and determine if the tested treatments could cause damage in the future. The
treated samples were artificially aged at a temperature of 80°C and 65% RH for 5 days
at the National Institute of Standards (NIS) in Cairo, Egypt. Artificial aging was per-
formed three days after samples were removed from the desiccators.




                                                                                                   Conservation science in Cultural Heritage




         Figure 3. Exposure of the samples to the essential oil vapors using a desiccator.


   2.5. Assessment methods

    Examination and measurements were made before oil exposure and after exposure
and artificial aging. Surface, optical (i.e. CIELAB color coordinates) and chemical proper-
ties of the tested samples (i.e. changes in chemical structure) were determined as follows.


                                                                                              83
                                                                                                                       2.5.1. Digital microscope

                                                                                                                        A SUPEREYES PZ01 500X USB Digital Microscope was used to document the
                                                                                                                    resultant forms of damage caused by exposure of the photographic samples to each
                                                                                                                    of the five selected essential oils and artificial aging.


                                                                                                                       2.5.2. Colorimetric measurements
M. Ali - Effect of five essential oils as green disinfectants on selected photographic prints: experimental study




                                                                                                                        The change in color was measured using a MiniScan Model No. EZ MSEZ0693. All
                                                                                                                    samples were measured in a visible region, with an interval of 10 nm using a D65 light
                                                                                                                    source and a viewing angle of 10 degrees. The CIELAB color parameters (L*, a*, b*)
                                                                                                                    were used, where L* defines lightness and varies from 0 (black) to 100 (white); a* rep-
                                                                                                                    resents the red/green axis, where +a means red and – a means green; b* represents
                                                                                                                    the yellow/blue axis, where +b means yellow and – a means blue. All values of L*, a*,
                                                                                                                    and b* were obtained before exposure to oil vapors, and after exposure and artificial
                                                                                                                    aging. Each reading was the average of three measurements. The total color differ-
                                                                                                                    ence ΔE* was also calculated from the following formula: ΔE* = (ΔL*2 + Δa*2 + Δb*2)½
                                                                                                                    [60-62]. The analysis was carried out at the Faculty of Archaeology, Cairo University.


                                                                                                                        2.5.3. Attenuated total reflectance Fourier transform infrared (ATR-FTIR)

                                                                                                                        Spectra were obtained using a Nicolet 380 Ft-IR Spectrometer, in the frequency
                                                                                                                    range of 4000 – 400 cm-1. The ATR accessory was a Thermo Scientific ™ Performer
                                                                                                                    Plate ZnSe Crystal with an angle of incidence of 45°. The diamond has an active area
                                                                                                                    of 1 mm in diameter and the depth of each scan was approximately 2 microns below
                                                                                                                    the surface. No sample preparation was necessary before scanning. The analysis was
                                                                                                                    carried out at the National Institute of Standards (NIS) in Cairo, Egypt.


                                                                                                                        3. Results and discussion

                                                                                                                        3.1. Digital microscopy

                                                                                                                        Visually speaking, in terms of surface characteristics (i.e. image color and sheen),
                                                                                                                    from no change to a very slight change was observed in all tested samples post expo-
                                                                                                                    sure and artificial aging (Figure 4). However, after exposure to clove oil, sample BCL1
                                                                                                                    showed drops of oil on the surface. Albumen prints showed the most change in color,
                                                                                                                    which is logically due to the artificial aging and not the oil vapor exposure, since albu-
                                                                                                                    men prints are known to be very sensitive to the surrounding environmental conditions
                                                                                                                    and over time tend to fade and yellow [10]. Sample CL2 showed dust particles on the
                                                                                                                    surface after exposure to lavender oil vapors and artificial aging.


                                                                                                                        3.2. Colorimetric measurements

                                                                                                                        The total color difference (ΔE*) is a value that is useful as an indicator of the difference
                                                                                                                    between the sample and the reference. In literature, a chromatic variation of 2-3 can be
                                                                                                                    considered noticeable by the human eye; however, it is clearly lower than the threshold
                                                                                                                    limit required (ΔE* = 5) for the maintenance and restoration of historical surfaces [63].


                                                                                                84
    The obtained results show from an insignificant to minimal change for all three
color coordinates (i.e. L*, a* and b*) in the silver gelatin and chromogenic print sample
sets. On the other hand, measured L*, a*, and b* values for albumen prints showed
extreme changes for both Dmin and Dmax areas due to the artificial aging of the
samples rather than oil exposure. Results are presented in Table 2. All samples showed
total color change below 5 (ΔE*≤ 5) excluding BA2, BC1 and CC2, which showed ΔE*
values of 5.97, 5.90 and 6.36, respectively (Figure 5).




                                                                                                         Conservation science in Cultural Heritage
Figure 4. Microscopic inspection of photographic samples before exposure to vapors of: A) anise,
B) cinnamon, C) clove, D) lavender and E) thyme oils and after exposure and artificial aging.




Figure 5. Measured ΔE* values for photographic samples after exposure to vapors of oils and arti-
ficial aging.


                                                                                                    85
                                                                                                                    Table 2. Measured L*a*b* values for photographic samples before and after exposure to vapors
                                                                                                                    of oils and artificial aging


                                                                                                                                            Samples                               L*        a*          b*
                                                                                                                                                        Anise-treated samples
                                                                                                                                        Before anise oil exposure                64.21     4.89       22.22
                                                                                                                      AA1
M. Ali - Effect of five essential oils as green disinfectants on selected photographic prints: experimental study




                                                                                                                               After anise oil exposure and artificial aging     57.42     4.20       16.28
                                                                                                                                        Before anise oil exposure                51.46     6.46       14.97
                                                                                                                      AA2
                                                                                                                               After anise oil exposure and artificial aging     45.70     4.49       11.20

                                                                                                                      BA1               Before anise oil exposure                74.63     1.39       14.31
                                                                                                                               After anise oil exposure and artificial aging     71.26     1.25       11.57

                                                                                                                      BA2               Before anise oil exposure                34.83     0.51        5.25
                                                                                                                               After anise oil exposure and artificial aging     29.19     0.27        3.29

                                                                                                                      CA1               Before anise oil exposure                75.17    13.51       14.43
                                                                                                                               After anise oil exposure and artificial aging     73.38    13.64       11.22
                                                                                                                                        Before anise oil exposure                30.43    33.19        6.93
                                                                                                                      CA2
                                                                                                                               After anise oil exposure and artificial aging     31.67    33.28        5.45
                                                                                                                                                      Cinnamon-treated samples
                                                                                                                                     Before cinnamon oil exposure                58.73     4.85       20.84
                                                                                                                      AC1
                                                                                                                             After cinnamon oil exposure and artificial aging    43.95     3.25       12.02
                                                                                                                                     Before cinnamon oil exposure                51.57     5.02       16.57
                                                                                                                      AC2
                                                                                                                             After cinnamon oil exposure and artificial aging    35.30     3.20        9.20

                                                                                                                      BC1            Before cinnamon oil exposure                97.99     0.96        6.44
                                                                                                                             After cinnamon oil exposure and artificial aging    92.30     2.08        5.37

                                                                                                                      BC2            Before cinnamon oil exposure                31.91     0.47        2.14
                                                                                                                             After cinnamon oil exposure and artificial aging    29.92     0.49        1.48
                                                                                                                                     Before cinnamon oil exposure                81.30     4.08       13.37
                                                                                                                      CC1
                                                                                                                             After cinnamon oil exposure and artificial aging    84.98     5.58       11.76
                                                                                                                                     Before cinnamon oil exposure                40.30    29.66       17.53
                                                                                                                      CC2
                                                                                                                             After cinnamon oil exposure and artificial aging    38.98    29.72       11.30

                                                                                                                                                        Clove-treated samples

                                                                                                                                        Before clove oil exposure                60.46     5.53       23.33
                                                                                                                     ACL1
                                                                                                                               After clove oil exposure and artificial aging     49.88     4.60       14.87
                                                                                                                                        Before clove oil exposure                46.70     6.46       16.87
                                                                                                                     ACL2
                                                                                                                               After clove oil exposure and artificial aging     38.36     4.61       11.25



                                                                                                 86
BCL1             Before clove oil exposure                 78.69    2.62    18.46
        After clove oil exposure and artificial aging      78.12    1.45    13.42

BCL2             Before clove oil exposure                 27.25    1.00    5.41
        After clove oil exposure and artificial aging      26.80    0.68    4.90
                 Before clove oil exposure                 78.34    6.08    9.71
CCL1
        After clove oil exposure and artificial aging      78.90    6.41    8.62

CCL2             Before clove oil exposure                 26.64   32.75    5.02
        After clove oil exposure and artificial aging      26.12   29.11    3.33
                                Lavender-treated samples
               Before lavender oil exposure                62.64    6.94    27.34
AL1
       After lavender oil exposure and artificial aging    47.50    3.96    13.96
               Before lavender oil exposure                51.53    6.53    19.59
AL2
       After lavender oil exposure and artificial aging    44.51    4.14    11.54

BL1            Before lavender oil exposure                97.10   - 0.46   7.92
       After lavender oil exposure and artificial aging    93.68   - 0.37   6.52

BL2            Before lavender oil exposure                58.37    0.66    8.98
       After lavender oil exposure and artificial aging    54.53    0.17    5.81

CL1            Before lavender oil exposure                79.01   11.42    21.42
       After lavender oil exposure and artificial aging    78.58   11.14    17.22




                                                                                         Conservation science in Cultural Heritage
               Before lavender oil exposure                38.14   26.82    24.96
CL2
       After lavender oil exposure and artificial aging    36.14   28.74    21.67

                                 Thyme-treated samples
                 Before thyme oil exposure                 54.68    5.92    21.44
AT1
        After thyme oil exposure and artificial aging      49.42    5.70    17.01
                 Before thyme oil exposure                 51.77    7.32    19.35
AT2
        After thyme oil exposure and artificial aging      41.89    5.07    12.78

BT1              Before thyme oil exposure                 89.84    0.85    11.39
        After thyme oil exposure and artificial aging      85.41    0.76    9.60

BT2              Before thyme oil exposure                 30.99    0.66    6.78
        After thyme oil exposure and artificial aging      31.20    0.56    4.23

CT1              Before thyme oil exposure                 94.87    1.31    13.26
        After thyme oil exposure and artificial aging      94.29    1.93    11.65

CT2              Before thyme oil exposure                 32.64   31.79    7.04
        After thyme oil exposure and artificial aging      31.47   29.63    4.60



                                                                                    87
                                                                                                                        3.3. Attenuated total reflectance Fourier transform infrared (ATR-FTIR)

                                                                                                                        FT-IR spectra for the tested samples show the absorption bands characteristic of
                                                                                                                    protein. Amide I and amide II are the most prominent vibrational bands of protein [64].
                                                                                                                    The amide I band within the 1600-1700 cm-1 region primarily originates from the C=O
                                                                                                                    stretching vibrations of the peptide linkage (70 – 85%) [65, 66]. The amide II band
                                                                                                                    within the 1500 – 1600 cm-1 region corresponds to a combination of several types of
                                                                                                                    vibrations, in-plane N-H bending (40 – 60 %), C-N stretching vibrations (18 – 40%) and
M. Ali - Effect of five essential oils as green disinfectants on selected photographic prints: experimental study




                                                                                                                    C-C stretching vibrations (about 10%) [66, 67]. The absorption band at around 3600
                                                                                                                    – 3100 cm-1 corresponds to OH stretching vibrations and the 1160 – 898 cm-1 region
                                                                                                                    corresponds to C-O stretching of COH/C-O-C [68] (Figure 6).




                                                                                                                    Figure 6. FT-IR spectra representing the Dmin area in blue and the Dmax area in red for the albu-
                                                                                                                    men print sample set compared to the equivalent areas, in green and black, respectively, post
                                                                                                                    exposure to vapors of the selected essential oils and post artificial aging.


                                                                                                                        Based on the obtained ATR-FTIR spectra, samples treated with lavender oil vapors
                                                                                                                    showed no change, as in the case of the albumen print sample (AL) (Figure 6) and the
                                                                                                                    silver gelatin print sample (BL) (Figure 7), and a very minor change in the OH stretching
                                                                                                                    vibration in the case of the chromogenic print sample (CL) (Figure 8). For the albumen


                                                                                                 88
sample set, the resultant spectra showed an increase in the OH stretching band indi-
cating more hydrogen bonding, which may be due to the hydrolysis of the albumen.
Sample AA treated with anise oil and sample AC treated with cinnamon oil exhibited an
increase in the intensity of the amide I band which is also associated with albumen
hydrolysis. The increase in the width of the amide I band in sample AC is an indication
of the oxidation of the protein [69]. The sample treated with clove and thyme showed
insignificant changes (Figure 6). The cinnamon and thyme treated silver gelatin prints
showed a very slight change in the OH stretching and amide I and amide II bands.
Changes in the amide I band were observed in the case of sample BA treated with anise
and BCL treated with clove (Figure 7).




                                                                                                          Conservation science in Cultural Heritage




Figure 7. FT-IR spectra representing the Dmin area in blue and the Dmax area in red for the silver
gelatin print sample set compared to the equivalent areas, in green and black, respectively, post
exposure to vapors of the selected essential oils and post artificial aging.


     For the chromogenic print sample set, all treated samples showed minor changes
in the OH stretching band when compared to standard samples, with the sample treated
with lavender showing the least change (Figure 8).


                                                                                                     89
M. Ali - Effect of five essential oils as green disinfectants on selected photographic prints: experimental study




                                                                                                                    Figure 8. FT-IR spectra representing the Dmin area in blue and the Dmax area in red for the
                                                                                                                    chromogenic print sample set compared to the equivalent areas, in green and black, respectively,
                                                                                                                    post exposure to vapors of the selected essential oils and post artificial aging.



                                                                                                                        4. Conclusion

                                                                                                                         Based on available literature, the antimicrobial activities of the five essential oils
                                                                                                                    (i.e. lavender, clove, anise, cinnamon and thyme) selected for this study are well es-
                                                                                                                    tablished. It has been proven that the tested oils are capable of inhibiting or slowing the
                                                                                                                    growth of bacteria and molds. Results also showed that the antimicrobial activities of
                                                                                                                    essential oils are different, depending on the type of microorganisms and the type and
                                                                                                                    concentration of each oil. Essential oils with a high concentration of phenolic com-
                                                                                                                    pounds such as clove and thyme are the most effective, even at low concentrations.
                                                                                                                    On the other hand, scientific publications provide extremely limited data about the ef-
                                                                                                                    fect of essential oils in vapor phase on the properties of photographs and thus, their po-
                                                                                                                    tential use in the preservation of valuable photograph collections. Based on the obtained
                                                                                                                    data from visual inspection, microscopic examination, colorimetric measurements and
                                                                                                                    ATR-FTIR spectroscopy, this research has shown that all tested essential oils in vapor
                                                                                                                    phase have little or no effect on the selected photographic materials (i.e. albumen, silver


                                                                                               90
gelatin and chromogenic prints). Visually speaking, all tested samples showed either no
change to only a slight change in image surface characteristics (i.e. color and sheen).
Obtained ∆E* values were ≤ 5 in most tested samples, which is within the accepted
limit for the maintenance and restoration of historical surfaces. In terms of chemical
changes, all oil vapors showed insignificant changes in positions and intensities of the
OH stretching, amide I and amide II characteristic IR bands of proteins (i.e. albumen
and gelatin) after treatment and artificial aging. However, lavender oil gave the best re-
sults with all types of tested photographic prints in terms of preserving the optical and
chemical properties of the photographs. This research does not include the effect of the
oil on the image silver, chemically speaking. Moreover, the prepared albumen prints
showed a major change in color post oil vapor exposure and artificial aging, which is
more likely due to the aging conditions rather than the oil treatment. Naturally aged al-
bumen prints were not an option since they were not available for experimental use.
    In brief, essential oils in vapor phase can be safely used as natural biocides on albu-
men, silver gelatin and chromogenic prints for the control of biodegradation as alterna-
tives to the currently available synthetic chemicals which are either hazardous or
have detrimental effects on photographic collections. Exposure of photographs to the
volatile compounds of essential oils can be performed in a desiccator cabinet or a clean
chamber, in the case of over-sized objects. The duration of exposure is 15-20 days.


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   Biographical notes

    Maha Ali is currently a lecturer of photograph conservation at the Faculty of Ar-
chaeology, Cairo University. She received her doctorate degree in Conservation from
Cairo University in 2016. She has also taught several photograph conservation class-
es at post graduate level in a joint International Master’s Program in Conservation of
Antique Photographs and Paper Heritage between Helwan University, Egypt and the
University of Catania, Italy. She has held a number of workshops in Egypt, Lebanon,
and Morocco with the aim of raising awareness on the significance of photograph
heritage in Egypt and the Middle East and their preservation needs. She has also de-
livered a lecture on “Solvent Cleaning of Silver Gelatin prints: Is It Safe?” for staff mem-
bers, and students at undergraduate and postgraduate level at the Ca’ Foscari Univer-


                                                                                               95
                                                                                                                    sity of Venice, Department of Philosophy and Cultural Heritage, School of Cultural
                                                                                                                    Production and Conservation of the Cultural Heritage in January 2017. Maha has pub-
                                                                                                                    lished several papers discussing different issues related to photograph and paper con-
                                                                                                                    servation.


                                                                                                                       Summary
M. Ali - Effect of five essential oils as green disinfectants on selected photographic prints: experimental study




                                                                                                                        Albumen, silver gelatin and chromogenic prints are found abundantly among pho-
                                                                                                                    tographic collections in Egypt. Due to the uncontrolled environment in archives and li-
                                                                                                                    braries, this precious visual heritage with its high protein and cellulose content pro-
                                                                                                                    vides the right culture medium required for fungal growth. Many essential oils have
                                                                                                                    been proven to have antibacterial and antifungal properties. Essential oils offer a safe
                                                                                                                    alternative to other common disinfection methods; however, their effect on the proper-
                                                                                                                    ties of photographs have not received much study. This paper studies the effect of
                                                                                                                    vapors of anise, cinnamon, clove, lavender and thyme oils on albumen, silver gelatin
                                                                                                                    and chromogenic prints, to find a proper disinfection method that is user-friendly and
                                                                                                                    environmentally safe and respects the nature of photographic materials. Essential oils
                                                                                                                    were provided by the National Research Center (NRC) in Cairo, Egypt. Artificially aged
                                                                                                                    albumen prints, and naturally aged silver gelatin and chromogenic prints were exposed
                                                                                                                    in desiccators to the selected essential oils in the vapor phase for a period of 5 days.
                                                                                                                    All samples were artificially aged at a temperature of 80°C and 65% RH for a period of
                                                                                                                    5 days to study the long-term effects of the tested treatments. Treatments were evalu-
                                                                                                                    ated using several techniques including visual inspection, microscopic inspection,
                                                                                                                    colorimetric measurements, and attenuated total reflectance Fourier transform infrared
                                                                                                                    spectroscopy. Results showed that all tested essential oils had a very slight effect on the
                                                                                                                    tested photographic samples; however lavender oil was found to be the best option,
                                                                                                                    specifically in terms of preserving the chemical properties of the photographic surfaces.


                                                                                                                       Riassunto

                                                                                                                         Albumine, gelatine d’argento e stampe cromogeniche si trovano in abbondanza nel-
                                                                                                                    le collezioni fotografiche in Egitto. A causa dell’ambiente non controllato negli archivi e
                                                                                                                    nelle biblioteche, questo prezioso patrimonio visivo con il suo alto contenuto di protei-
                                                                                                                    ne ​​e cellulosa fornisce il terreno di coltura per la crescita dei funghi. Molti oli essenzia-
                                                                                                                    li hanno dimostrato di avere proprietà antibatteriche e antimicotiche. Gli oli essenziali
                                                                                                                    offrono un’alternativa sicura ad altri metodi di disinfezione comuni; tuttavia, non ci sono
                                                                                                                    molti studi sul loro effetto sulle proprietà delle fotografie. Questo articolo descrive l’ef-
                                                                                                                    fetto dei vapori di oli di anice, cannella, chiodi di garofano, lavanda e timo su albumine,
                                                                                                                    gelatina d’argento e stampe cromogeniche, per trovare un metodo di disinfezione ade-
                                                                                                                    guato che sia facile da usare e sicuro per l’ambiente nel rispetto dei materiali fotogra-
                                                                                                                    fici. Gli oli essenziali sono stati forniti dal National Research Center (NRC) deI Cairo,
                                                                                                                    in Egitto. Stampe all’albume invecchiate artificialmente, gelatine d’argento invecchiate
                                                                                                                    naturalmente e stampe cromogeniche sono state esposte in essiccatori agli oli essen-
                                                                                                                    ziali selezionati in fase vapore per un periodo di 5 giorni. Tutti i campioni sono stati
                                                                                                                    invecchiati artificialmente a una temperatura di 80 °C e 65% di umidità relativa per un
                                                                                                                    periodo di 5 giorni per studiare gli effetti a lungo termine dei trattamenti testati. I tratta-
                                                                                                                    menti sono stati valutati utilizzando diverse tecniche tra le quali ispezione visiva, ispe-


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zione microscopica, misurazioni colorimetriche e spettroscopia a infrarossi in trasfor-
mata di Fourier a riflettanza totale attenuata. I risultati hanno mostrato che tutti gli oli
essenziali testati hanno avuto un lieve effetto sui campioni fotografici testati; l’olio di
lavanda è risultato essere l’opzione migliore, in particolare, in termini di salvaguardia
delle proprietà chimiche delle superfici fotografiche.




                                                                                                    Conservation science in Cultural Heritage




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