Liquid silver gelatin works well on stone. Preparation is very important. I always apply a liquid sealer (DIP Invisivel). If the stone is a very porous one then I apply a water based non colour varnish. Before doing this it is essential to remove all the dust left from sanding. A anti-uv varnish is essential to finish. The last image below is of a portrait on stone mounted in Alfama, Lisbon. It is out of direct sunlight.
Printing on walls
For me printing directly onto a wall, especially outdoors, is the most exciting. The wall must be plastered with a fine plaster and the finish is best when it is smooth… and then it is be sealed. It is a good idea to put a hardener on it to help the emulsion take to the wall and make it more resistant. For outdoors I have a mobile darkroom with a window at one end which we fix against the wall around where the image is to be printed. The liquid silver gelatin I apply (in dark with red light). It takes about 2 hours to dry. I use a projector to expose the negative, followed by the standard darkroom process of dev, stop and fix. Washing is essential. To be on the safe side I use hypo followed by 45 minutes washing with a hose pipe.
Printing on wood
I use a maritime plaster board with a pine finish. This is so it will dry flat (with pured wood and with big pieces you get curves). I always use a varnish. If you want to paint it first use a water base paint, sand it when dry and then apply a water based varnish. In the images below are test pieces in the first image. The second shows me settting up in my darkroom to print an image on wood using my slide projector. In the third I am washing the piece in a big sink made of black plastic in a wood frame ( I now wash the pieces upright).