Along with being a cool mental image, Liquid light is liquid emulsion produced by Rockland Colloid. About $28 will get you 16 ounces of what is essentially a silver gelatin emulsion suspended in a liquidy latex base. Liquid Light can be applied to just about any surface you might want to sensitize, including metal, fabric, stone, yourself (highly discouraged, photo chemistry is quite toxic) or just about anything that can stand to be immersed in fluids for the length of time that it takes to process the image (note: this does not include acoustic tiling, I've had bad experiences when a colleague tried that one time.). Liquid Light starts out as a solid and must sit in a pan of warm water before it can be poured out of the bottle. After coating the object, letting it dry, exposing, processing and drying, you end up with a photographic image on the oddest of things.