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Glass plate negative

The conservation and restoration of photographic plates is caring for and maintaining photographic plates to preserve their materials and content. It covers the necessary measures that can be taken by conservators, curators, collection managers, and other professionals to conserve the material unique to photographic plate processes. This practice includes understanding the composition and agents of deterioration of photographic plates, as well as the preventive conservation and interventive conservation measures that can be taken to increase their longevity.

History

Composition

Photographic plates consist of an image layered on a glass support. Glass plates emerged as a common support medium for photographic negatives in the mid-nineteenth century. In general, black and white photographic negatives are made up of fine silver particles (or color dyes for color negatives), which are embedded in a thin layer called a binder. Combined with the image substance, these two elements comprise the emulsion. This emulsion layer sits upon what is called the support, which can be paper, metal, film, or as in the case of photographic plates, glass.[1] Depending upon the period, there can be variants to the binder and thus, the chemistry of the image. This is extremely important with the conservation and restoration of photographic plates because it helps the conservator prevent further chemical reactions. In the case of the Wet Plate Collodion, the image is run under a wash bath to stop the development of the image after exposure. An important part of the photographic process, "fixing", is then used to wash the silver particles that are not part of the image, which then produces a stable negative image. The fix bath will ensure that the remaining silver halide crystals are no longer sensitive to additional light exposure, removing all excess. This negative image can then be used over many years to produce paper positives. Glass plates as a form of support were popular in use between 1851 and the 1920s.[2]

Processes

Early wet plate collodion portrait of lady

Agents of deterioration

There are ten accepted agents of deterioration: dissociation, fire, incorrect relative humidity, incorrect temperature, light, pests, pollutants, physical forces, thieves, and water.[9] Photographic plates face risks of damage from both external forces and from leaves own chemical composition. For a conservator to create an appropriate plan to protect against agents of deterioration, they must understand what might impact a photographic plate. The following list addresses how each agent of corruption harms photographic glass plates.

Relative humidity and temperature

Relative humidity (RH) and temperature are two of the most common threats to photographic plates.[10] As with all material collections, high temperature in combination with high humidity can cause mold growth and attract pests.

Photographic plates face significant structural and chemical challenges unique to their makeup. There are two types of photographic glass plates; collodion wet plates and gelatin dry plates. Structurally, collodion wet plates are held together with a specific emulsion type, made using a silver halide mixture in gelatin. Fluctuations in RH can strain the adhesive emulsion, causing the gelatin to expand and contract. The strain from incorrect RH can also cause the emulsion to crack or separate along the plates' edges.[10] With gelatin dry plates, high humidity can cause mold to grow on the emulsion.[11] High levels of humidity can cause glass plates that have been stored incorrectly to stick together, compromising the image on the plate. Increasing RH can cause deterioration of other elements; these include the silver halide, varnish, and glass support. Decreasing the RH will cause deterioration by eventually leading to the flaking of the binder and dehydration of the glass.[12]

Much like RH, temperatures must be precise and closely monitored for the correct storage of photographic glass plates. A safe temperature to keep glass plates is 65 °F (18 °C); however, a fluctuation of +/- 2 °F (−17 °C) would not cause a significant impact, making the safest range 63 to 67 °F (17 to 19 °C).[13] Low temperatures aid in slowing a plate's inherent vice by delaying the chemical reactions that cause decay of the plate's structure. Increasing temperatures or frequently high fluctuations will speed up the decay process.

Theft and dissociation

Although theft and dissociation can occur separately, it is not uncommon for the two to go hand-and-hand and co-occur. Dissociation typically results in overtime from an ordered system falling apart due to lack of routine maintenance updates or from a catastrophic event leading to data loss.[14] If an inventory is not regularly updated it could become easy for a single, or several, glass plates to go missing. Regular inventory maintenance can also serve as a deterrent against theft. Ensuring glass plates are locked and stored where only designated museum staff can access them is the best preventative measure against theft.

Water and pests

Deterioration in glass is often directly related to moisture, from humidity or direct contact.[13] Enough moisture over time will result in the chemical composition of the image to change. In the 1990s, The United States National Archive began to notice that some glass plates featured in their collection, on the non-photo bearing side of the scale, a crystalline deposit, known as sick-glass, was present.[13] If a glass plate has been subject to large amounts of moisture, it could grow mold on the plate's emulsion. Mold will eat away at the emulsion and attract other living pests. Insects will be more likely to appear in areas already compromised by inappropriate storage conditions. Insects will produce waste materials that, like dust, build up over time, causing further damage. Pests eat glass plate storage materials such as paper envelopes or cardboard boxes.

Light

Photographic plates and all photographic materials are susceptible to light. Extensive and ongoing exposure to light can cause significant and irreversible deterioration. Sunlight is the most damaging type of light to photographic plates. However, indoor lighting and other forms of UV lighting all pose a threat to photographic plates causing fading and yellowing.[15] Light is especially threatening to color photographic materials as it causes accelerated fading of the color dyes.[16] Exposure to light could deteriorate and lead to discoloration of the pigments present on the plate.

Pollutants and fire

Air pollution can threaten photographic plates through poor air quality and dirt that can damage the materials. This can include dust to gaseous pollution in an urban environment. Air pollution can cause fading of photographic materials. If a plate is subject to poor air quality, debris removal must be done with care using a cotton cloth; if done incorrectly, the glass might be subject to abrasions.[17] Other sources of air pollution include "photocopying machines, construction materials, paint fumes, cardboard, carpets, and janitorial supplies", and other types of outdated media.[15]

Fire can cause severe damage to photographic glass plates. The heat produced by a fire can aid in increasing the chemical decomposition rate of the plate's emulsion. Pollutants in the air produced by the fire, smoke and debris can also attach or rest upon plates. The same care should be taken removing trash from a fire that would be used to remove dust and other air pollutants.

Material and chemical

The glass composition of photographic plates can be a factor of deterioration. Due to poor quality or an inherent vice, "sick glass" can occur. Environmental conditions are usually linked to the increase or presence of this glass corrosion. The effect of "sick glass" can be weeping and crizzling caused by excessive alkali and a lack of stabilizers.[12] Weeping involves droplets forming on the glass that appear as tiny crystals. This deterioration is especially threatening for cased photographs because the cover glass could be corroded and damage the image underneath.[18] Corrosion of the glass plate support can also damage the image layer by causing the lifting of the binder and varnish layers.[13]

The other chemical components of glass plate negatives can also be threatening agents of deterioration. For instance, the silver image layer could undergo oxidative deterioration, leading to fading and discoloration. Additionally, the collodion binder itself is made up of cellulose nitrate, which is known to be a highly flammable compound. Most of these agents of deterioration are the result of poor chemical processing as a result of inherent vice, but poor environmental and storage conditions usually accelerate them.[13]

Broken glass plate – Avdella, izgorena, 1905

Physical

Glass plates are relatively stable dimensionally but also very fragile and brittle.[10] Glass is breakable and highly susceptible to breakage, cracks, and fractures. This can be caused by human error, including dropping or bumping the glass plate, or it can be caused by failure of storage equipment, housing, shelves, etc., which may lead to an impact to the glass. Different breakage and stress states affect the image layer and binder differently.

Types of breakage:[12]

Preventive conservation

Environment

Environmental controls are a crucial part of the preservation of photographic glass plates. Relative humidity (RH), temperature, and light play a significant role in keeping the multiple materials in photographic glass plates maintained. The following regulatory measures are taken for their preservation:

Handling

Photographic glass plates are handled carefully to avoid physical or chemical deterioration and damage – the following aids in their preservation through proper handling:

Storage

Storage and housing of photographic glass plates is important to their preservation. Museums and other cultural institutions take the following measures to ensure their glass plates are properly housed:

Storage of broken photographic plates

Broken or cracked glass plates are stored specially, separate from other photographic plates, and in the following ways:

Maintenance/housekeeping

Maintenance/housekeeping of photographic plates requires minimal intervention:

Conservation treatment

Broken or cracked glass plates compose many needing conservation treatment. There are various actions taken in reassembling and restoring these plates using the following materials and methods:

Handling

Adhesives

Conservators use no ideal adhesive; each bond has benefits and disadvantages for different situations.

Backing material

Application

Repair methods and techniques

Projects

The vertical assembly method along with a light line is used in The Glass Plate Negative Project at the Heritage Conservation Centre as outlined in the case study. This study shows how conservators also deal with other conservation issues, including accretions and residue. For instance, while the plates were considered structurally stable, they may have needed surface cleaning. This was completed by using swabs dampened with water/ethanol solutions to reduce stains or do away with any left tape residue. Pressure-sensitive labels were removed mechanically. Conservators used Whatman lens tissues to wipe off any other residue marks.[35]

References

  1. ^ a b c d Valverde, Maria Fernanda. "Photographic Negatives: Nature and Evolution of Processes" (PDF). Image Permanence Institute. Advanced Residency Program in Photograph Conservation. Retrieved 4 April 2018.
  2. ^ Somerset Photography. "Glass Negatives". History of Photography. Retrieved 4 April 2018.
  3. ^ Paris Photo. "Collodion Glass Plate Negative". Paris Photo. Retrieved 5 April 2018.
  4. ^ Graphics Atlas. (n.d.). Wet Plate Collodion. Graphics Atlas: Identification. Retrieved May 1, 2022, from http://www.graphicsatlas.org/identification/?process_id=352
  5. ^ Graphics Atlas. (n.d.). Gelatin Dry Plate. Graphics Atlas: Identification. Retrieved May 1, 2022, from http://www.graphicsatlas.org/identification/?process_id=303
  6. ^ a b Image Permanence Institute. (n.d.). Identification. Graphics Atlas: Screen Plate. Retrieved May 14, 2022, from http://www.graphicsatlas.org/identification/?process_id=301#overview
  7. ^ Science Media Museum. (2020, April 24). History of the autochrome. National Science and Media Museum blog. Retrieved May 14, 2022, from https://blog.scienceandmediamuseum.org.uk/autochromes-the-dawn-of-colour-photography/
  8. ^ Image Permanence Institute. (n.d.). Identification. Graphics Atlas: Ambrotype. Retrieved May 14, 2022, from http://www.graphicsatlas.org/identification/?process_id=283
  9. ^ "Agents of deterioration". Canadian Conservation Institute. 26 September 2017.
  10. ^ a b c Hendriks, Klaus B.; Iraci, Joe. "Care of Black-and-White Photographic Glass Plate Negatives – Canadian Conservation Institute (CCI) Notes 16/2". Government of Canada. Minister of Public Works and Government Services Canada. Retrieved 6 April 2018.
  11. ^ Casella, Luisa. "Gelatin Dry-plate". AIC Wiki. Retrieved 6 April 2018.
  12. ^ a b c d e f g h i j k l Whitman, Katharine. "Preservation of Glass in Photographic Materials". AIC Wiki. Retrieved 25 March 2018.
  13. ^ a b c d e Bahnemann, Greta. "Preservation of Glass Plate Negatives". WebJunction. Retrieved 29 April 2022.
  14. ^ Waller, Robert; Cato, Paisley. "Agents of Deterioration: Dissociation". Government of Canada. Retrieved 27 April 2022.
  15. ^ a b c NEDCC Staff. "5.3 Care of Photographs". NEDCC. Retrieved 6 April 2018.
  16. ^ Northeast Document Conservation Center. "Storing Photograph Collections". NEDCC. Retrieved 6 April 2018.
  17. ^ Cappucci, Terri. "Glass Plate Negatives". Retrieved 30 April 2022.
  18. ^ McElhone, John P. "Cased photographs: Including Daguerreotypes, Ambrotypes (Collodion Positives), and Tintypes". AIC Wiki. American Institute for Conservation of Historic and Artistic Works. Retrieved 7 April 2018.
  19. ^ Northeast Document Conservation Center. "Storing Photograph Collections". NEDCC. Retrieved 25 March 2018.
  20. ^ Voellinger, T. (2009). Cold Storage for Photographs Collections – An Overview . Conserve O Gram , 14(10), 1–5. Retrieved April 27, 2022, from https://www.nps.gov/museum/publications/conserveogram/14-10.pdf.
  21. ^ American Institute of Conservation. (n.d.). PMG Silver Mirroring. Wiki. Retrieved May 2, 2022, from https://www.conservation-wiki.com/wiki/PMG_Silver_Mirroring#:~:text=Silver%20Mirroring%20is%20a%20result,the%20substrate%20or%20image%20particles.
  22. ^ Library of Congress. "Care, Handling, and Storage of Photographs". Library of Congress. Retrieved 25 March 2018.
  23. ^ Herskovitz, R. (1999). Storage of Glass Plate Negatives. Minnesota History Interpreter, 3–6. Retrieved April 2022, from https://www.mnhs.org/sites/default/files/lhs/techtalk/techtalkjuly1999.pdf.
  24. ^ a b c d e f National Archives. "How Do I House Glass Plate Negatives?". National Archives. Retrieved 25 March 2018.
  25. ^ Hendriks, Klaus B.; Iraci, Joe. "Care of Black-and-White Photographic Glass Plate Negatives – Canadian Conservation Institute (CCI) Notes 16/2". Government of Canada. Minister of Public Works and Government Services Canada. Retrieved 7 April 2018.
  26. ^ Herskovitz, R. (1999). Storage of Glass Plate Negatives. Minnesota History Interpreter, 3–6. Retrieved April 2022, from https://www.mnhs.org/sites/default/files/lhs/techtalk/techtalkjuly1999.pdf.
  27. ^ a b Gaylord Archival. "Caring for Glass Plate Negatives". Gaylord Archival. Retrieved 25 March 2018.
  28. ^ Image Permanence Institute. (n.d.). Photographic activity test. Retrieved April 27, 2022, from https://www.imagepermanenceinstitute.org/tests/pat.html
  29. ^ Herskovitz, R. (1999). Storage of Glass Plate Negatives. Minnesota History Interpreter, 3–6. Retrieved April 2022, from https://www.mnhs.org/sites/default/files/lhs/techtalk/techtalkjuly1999.pdf.
  30. ^ Northeast Document Conservation Center. "Storing Photograph Collections". NEDCC. Retrieved 25 March 2018.
  31. ^ Hendriks, Klaus B.; Iraci, Joe. "Care of Black-and-White Photographic Glass Plate Negatives – Canadian Conservation Institute (CCI) Notes 16/2". Government of Canada. Minister of Public Works and Government Services Canada. Retrieved 25 March 2018.
  32. ^ Museum of the White Mountains. (n.d.). Cleaning, scanning, digitizing and Rehousing: A journey with glass plate negatives. Retrieved April 27, 2022, from https://www.plymouth.edu/mwm/intern-story-2/
  33. ^ American Institute for Conservation of Historic and Artistic Works. "Caring for Your Treasures". AIC. Retrieved 3 April 2018.
  34. ^ "PMG Preservation of Glass in Photographic Materials – Wiki". www.conservation-wiki.com. Retrieved 2022-05-10.
  35. ^ Tay, Jam Meng. "The Glass Plate Negative Project at the Heritage Conservation Centre" (PDF). AIC. The American Institute for Conservation of Historic & Artistic Works. Retrieved 9 April 2018.