Coffee developers are developing silver salts. Silver salts are not as lo-tech, as I need.
Also fixing can be made in kitchen salt. Just the medium being developed or fixed is not enough lo-tech.
One can say "you can do silver gelatin easily". Paper is not lo-tech, gelatin, measuring cups, thermometers, clocks (!) and various salts are also not as lo-tech, as I need.

I was considering salted paper, but I can,t see easy way to make silver salt pure and easy enough.