These things are making a little comeback. Traditionally they're made by carving porcelain, but I know of at least one company doing something either photomechanically or electromechanically to produce (the molds for) them. Anyway, to make a long story boring, I was wondering what photomechanical means - such as an etchant - might exist to provide a deep enough relief to produce large format photolithophanes. I'm not thinking so much about etching metal plates as something softer like a plastic or rubber that can be used as a mold. This seems really far out there to me.