Collodion-Chloride Paper

Page Information	Page Information
Date initiated 	July 2016
Contributors 	Luisa Casella, Stephanie Watkins
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==Collodion-Chloride Printing-Out Paper (POP) - Glossy or Matte==
=== Historical Facts===
Introduced by M. Gaudin in La Lumiére in1861Eder, Josef Maria. History of Photography. Translated and Edited by Edward Epstean, Columbia University Press, 1945. p.376.. In 1884 Liesegang introduced a ready-made paper, under the commercial name "Aristotype"
Historic use period begins "in 1880 when clay coated paper stock was adopted for photography" (Osterman, 2007)
The process gained popularity for its ability to produce finely detailed photographic prints and replaced albumen printing. It was predominantly used from the 1890s until the 1910s, most commonly for studio portraiture.
Matte collodion paper was introduced around 1893. Around the beginning of the 20th century, self-toning papers were sold.
=== Process Description ===
Collodion POP printing-out papers had a baryta layer that smoothed the surface and obscured paper fibers. The were coated with a collodion binder (which is a mixture of cellulose nitrate dissolved in ether and alcohol) and sensitized with silver salts that are light sensitive. To increase flexibility of the collodion, plasticizers such as glycerin and camphor oil could have been added. Papers were industrially produced. 
The paper is printed in contact with the negative. Printing is achieved directly without the need for development (hence the term "printing-out") and the image becomes visible during exposure, allowing photographers to gauge the correct exposure time visually. After exposure, the print is washed, toned with gold or platinum, and fixes in sodium thiosulfate. The toning process not only enhances stability of the image metal but alters the tonal range of the prints. Matte collodion usually underwent two separate toning baths of both gold and platinum and are often near neutral in tone.
=== Identification Characteristics===
Glossy collodion POP can be difficult to distinguish visually from gelatin POP, as they were used around the same period and present the same style of portraiture and formats, commonly adhered to secondary boards. Common formats are the carte-de-visite (about 4x5"), standard cabinet card (about 6.5x4.25"), boudoir cabinet card (about 8.5 x 5.25") or imperial cabinet card (about 9.75 x 6.75").
Another identification characteristic is that collodion shows a form of iridescent interference colors under fluorescent lights, in specular view.
==== Image material====
Collodion binder with photolytic silver image (possibly toned). Plasticizers such as glycerin and camphor oil can be present.
==== Color/ Tone ====
A range from warm-reddish to cool if toned with gold or platinum.
==== Support ====
Rag paper coated with baryta layer (gelatin with barium sulfate) - thin for matte collodion; thicker for glossy collodion.
Baryta layer would some times be tinted - commonly with a lavender, blue or rose toned dye. This is visible in the white areas of the image. These dyes tend to form a lake (barium salt version of the dye) with the barium sulphate in the baryta and therefore become very resistant to fading.
=== Deterioration ===
Silver mirroring is uncommon but possible with glossy collodion prints.
Collodion may become brittle with the loss of plasticizers, leading to the formation of cracks.
Because collodion does not respond to moisture variations, it generally has resistance to fading and yellowing in comparison to other POP processes like albumen and gelatin POP.
Because the collodion layer is extremely thin, it is easily abraded resulting in scratches that present as image loss.
=== Conservation ===
==== Precautions ====
Collodion is generally soluble in alcohols and ketones so great care must be taken when surface cleaning.
Immersion is also discouraged as the support will expand but not the collodion layer, leading to cracks or differential physical distortion.
==== Surface cleaning ====
Image layer is easily abraded by any friction. Dry cleaning can be done with cosmetic sponges or soft brushes. 
Swabs dampened with distilled water can be used if the image layer is robust and has no mold damage or other physical damage.
=== Housing and Storage Considerations===
==== Housing ====
Polyester or polyethylene sleeves can be used, if visual consultation is required. These should be uncoated and free from plasticizers or other additives and have passed the PAT. Polyester is the most inert and stable but can generate static, so care should be taken to minimize dust attraction.
Housing in plastic sleeves has the risk of abrasion, when prints are inserted, and also trapping debris that can cause scratches.
Paper envelopes are softer and can be ideal so long as they don;t have sams that may damage the print..
Four-flap enclosures are ideal for their ability to protect prints from dust and handling while providing easy access. They also accommodate for the usual added thickness of the secondary support in collodion POP.
==== Storage Conditions ====
Storage recommendations for these materials are similar to other paper supports - 20% to 50% relative humidity, with under 10% variations; temperature below 65F.
There is no counter-indication to freezing collodion POP prints.
=== Exhibition ===
The guidelines for exhibiting collodion printing-out paper (POP) categorizes these as "moderately light-sensitive." Therefore, they should have a total exposure per year of 10,000 foot-candle hours (100,000 lux hours), with 3 foot-candles for 10 months or 5 foot-candles for 6 months at 10 hours per day, and should rest for a minimum of 2 years between display cyclesWagner, Sarah, et al. "Guidelines for Exhibition Light Levels for Photographs." Topics in Photographic Preservation, vol. 9, 2001, pp. 127-128..
=== Emergency Recovery ===
Collodion will not dissolve in the event of a water damage but supports will swell and collodion will not, which can result in delamination and planar distortion.
If the prints are wet, they should be rinsed in clear water and air-dried as quickly as possible. Lay the prints flat on absorbent materials such as blotting paper, and replace the blotting paper frequently to promote even drying.
=== References ===
=== Further Reading===
*Graphics Atlas. (n.d.). Collodion POP. Accessed June 5, 2024, from: http://www.graphicsatlas.org/identification/?process_id=222
*Pénichon, Sylvie. 1999. Differences in Image Tonality Produced by Different Toning Protocols for Matte Collodion Photographs. JAIC, Volume 38, Number 2, Article 2 (pp. 124 to 143). https://cool.culturalheritage.org/jaic/articles/jaic38-02-002_3.html
*Stulik, Dusan, and Art Kaplan. 2013. The Atlas of Analytical Signatures of Photographic Processes. Los Angeles, CA: Getty Conservation Institute. http://hdl.handle.net/10020/gci_pubs/atlas_analytical: http://www.getty.edu/conservation/publications_resources/pdf_publications/pdf/atlas_collodion.pd
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