If you want to be even more "period" you could underexpose a bit (how much is a matter for testing) and sandwich the dry, finished negative over black velvet in a simple frame to make a faux ambrotype. Scattered light from the developed silver will make the highlights show light against the black backing. I've thought about doing this with a monobath developer and minimum-liquid processer to be able to go dry-to-dry in something like 20 minutes on a push cart, and hand out original "ambrotypes" in a lunch break. My cameras are a little on the new side to look right for Wild West or Civil War reenactors, though -- might have to work on that.
Other authentically period processes (some a little faster than POP) are cyanotype -- cyanotype was the first printing process, predating glass negatives by 20-30 years (it was used for reproducing line drawings and making photograms before there were negatives to print with it) -- albumen, salted paper, or van Dyke, all of which are printing out processes (meaning you can expose the print by eye).
Cyanotype is especially good because of low toxicity (the chemicals are safe for children), and will print out fully in five to ten minutes in full summer sun; only water is needed as developer, and paper can be sensitized ahead of time and kept, at least for a while (there are a couple sources of commercially precoated paper, so the box life must be at least a few weeks), and since it's UV sensitive, you can load the printing frame in a good light as long as the UV is filtered out.
Salted paper is the next simplest, but the sensitized paper doesn't keep as well as cyanotype, and has some sensitivity to blue, so you have to work in safelight; in addition, you need silver nitrate solution to sensitize the pre-salted paper, and fixer to stabilize the image after exposure.
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