I've been picking away on a project at work for the past year or so--contacting about a 1000 glass plates from the 1880-1920 period. Most of them are in the 5x7, 6x9 inch type range, with some that are 8x10 or slightly larger. Some are in great shape, others are cracked and stained with flaking emulsions. It's a big project of making duplicate master and working negs in the end. It comes down to a couple cases of paper and 4x5 film, plus chemistry to process all that and selenium toner for the prints as well as the storage enclosures to rehouse the plates. The budget really got eaten up on the storage though, the paper and negs were only about half of it.
There's not enough money to make interpositives/dupe negs, and access prints. I did experiment a bit with interpositives by shooting them on 4x5 with a light box--then scanned these and got some pretty good positive digital images. But still, it's a wash in the end-because we need negs.
What I found worked best was Ilford MG Warmtone RC. I use an old nine lamp Burke & James contact printer on an Omega voltage stabilizer. I have this lamped with 7.5 watt and 25 watt bulbs. I change them out based on the density of the plate. I also use sheets of vellum to cut the intensity of the lamps if needed. The exposures are usually 3-5-10 seconds or so, the densest plates may be more like 30. There are 2 frosted glass diffusion panels in this printer, that I lay smaller pieces of tissue paper, vellum and black paper on to hold back areas. I can switch the lamps on & off to add or subtract density--dodge & burn if you like--as well. I also use a black sharpie, or graphite, or red china marker to shade in pieces of tracing paper to make masks.
I took the platen off the printer and replaced this with a heavy piece of glass scavenged off an old Kodak copy machine. Under this I glued a thick piece of foam. This way, I can hold the paper to the plate with less pressure than the platen lid. I bought about 6 packs of Multigrade filters and taped them together to make big sheets to slide into the top diffusion drawer on the printer. It works very well compared to making the print under an enlarger, plus you have the masking blades and can make a very clean border. You handle the plate less as well, since it has the lightsource underneath it and you lay the paper on top. You only have to move it twice.
Most of the ones I've done so far, I've had to flash the paper to cut the contrast. What I do is to make the print hard--about a grade or two higher than normal--and then I flash with an enlarger. This way, I expose on the contact printer for the shadows, and flash in the midtone & highlight density.
I make notes of each plate--where I use a densitometer to take spot readings and measure the density range. I've found that I can get a ballpark idea of exposure and contrast over the course of printing several plates-- I can then group them in batches and work this way.
This is just what works for me though--if we had more money, I'd probably try to do it on Centennial POP, but I'd still have to shoot a 4x5 neg in the end, so in the end, it doesn't really matter how we get there.
Hope this gives you an idea on how to do it using modern materials. Azo or would be a good way to do it with fiber paper, but the best way, from an archival point of view, is to actually make interpositives and duplicate negs on polyester based film.
Good luck--
KT
my opinions/not my employers.
