SILVER use in photographic emulsions was a practical and cheaper concession after gold and platinum. While I have never used any of these materials, personally, I have seen prints of plates made from them on display at the George Eastman House in Rochester, New York. They may still be there. Platinotypes [sp?] had twice the greyscale of silver which seemed contrasty by comparison. There were gold-based emulsions there, too, but I can't remember them.

The Gum Bichromate process is interesting because it produces a relief image on a glass plate after exposure to light and subsequent development. Unexposed emulsion is water soluable and washes off. Dye is added to the image and then it can be viewed.

Blue prints are iron-based emulsions that are developed by ammonia gas. (You need liquid to produce the gas.)

There are several more.

So, I would go with platinum instead of silver for its tonal gradation, excellent definition and long linear response for exposure. The prints are beautiful. It's probably expensive. Blueprints lack the tonal gradation and definition so I'd pass on using it for anything other than photograms and novelty prints. Oh, and to use for line copy reproductions. The gum-bichromate process has nice tonal rendition but lacks the ability to resolve detail which restricts it for photographic rendering.