Photostats
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Hi Carolyn,
One of the best resources out there for identifying office copying methods (and there are many!) is a book called “The Office Copying Revolution” by Ian Batterham. The book was published by the National Archives of Australia and can be hard to come by, but it is well worth the investment if you have a lot of this material in your collection.Here is a bit of information I lifted from Batterham’s chapter on Photostats:
Active use for Photostats (and Rectigraphs) is 1909-1975 with phasing out beginning in 1950. There are a few other machines that perform the same process, but the name Photostat became ubiquitous.
The process involves a camera fitted with a prism so a correctly-oriented image of a document could be directly recorded to a piece of photographic paper. Consequently, a Photostat will generally have white text on a black background. However, in 1953 Kodak found a way to get black text on white ground from the same process. Also, one could repeat the process of imaging a “negative” document to get a positive (black text, white ground). This could be helpful for you as an identification tool, if you indeed have black documents with white text on photographic paper.
The photographic papers used in Photostats were generally thinner than regular photographic paper, and lacked a baryta layer. They were also often supplied on a roll, so you may see unevenly cut edges. In general, one thing to look for to confirm you have a silver paper is silver mirroring- a thin metallic sheen that can develop on the surface of the paper over a dark area.
It is possible that Photostats would not have been thoroughly washed after processing, and could present a preservation problem. I believe they would be more harm to themselves than to neighboring materials, so it is not necessary to isolate them from other collection materials. I would recommend you store them in good-quality folders (acid and lignin free, PAT tested), and you may consider interleaving them depending on the volume in your collection.
I hope this is helpful and I am curious to hear whether others have experience in identifying these materials!
Best,
Maggie -
The University of Illinois Library Preservation Department has a fantastic identification guide called Preservation Self-Assessment Program (PSAP) which lists identification of many types of library materials, including office reprographics. Within that subheading are photostats.PSAP guide
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