gesso: gypsum or plaster of Paris spread on a surface to make it suitable for painting or gilding (or a surface so prepared)
plaster of paris: any of several gypsum cements; a white powder (a form of calcium sulphate) that forms a paste when mixed with water and hardens into a solid; used in making molds and sculptures and casts for broken limbs
silver chloride: a chloride used chiefly in the manufacture of photographic emulsions