This is just something that happened to occur to me this morning, while brewing a pot of tea, of all things.
Ferric oxalate (Fe2(C2O4)3), familiar to those who have dabbled in platinum/palladium printing, is a photo-sensitive chemical that reduces to ferrous oxalate (FeC2O4) upon exposure to ultraviolet light. If ferrous oxalate were “developed” with gallic acid or a suitable, soluble gallate salt, then the ferrous gallate (which is the key component of iron-gall ink) formed could create a dark, contrasty image.
I should point out that all this is conjecture, and practical experimentation would be needed to prove the theory.
From Jake von Slatt, a modder with a penchant for Steampunk, comes this walk-through on an electrolytic etching process that can be made from a black-and-white digital image. Electroetching (aka Galvanic etching) involves no corrosive etchant, and works like the electroplating process in reverse. The process described utilises xerographic toner (carbon) from a laser-printed negative as the resist.
Note: As well as brass, this process could be used with copper plates, or most other copper alloys.
Ralph Lambrecht, co-author of the wonderful Way Beyond Monochrome and of DarkroomMagic.com, has published a description of a digital-to-analogue process involving a full-size, inkjet-printed “digital negative”. The key strength of this process is that it allows the production of archival contact prints from digital images at home. The key weakness is that the quality is still limited by the printer that you use.