Asphaltum in an equal weight of methylated spirit is useful for writing on opal glass, as it will not peel. Break the asphaltum small, put it in the spirit, and set it near a fireplace for two or three hours. It may be thinned by adding spirit. Apply two coats thin, rather than one thick. Sealing wax treated the same way in spirit of wine, and applied hot, is good for polished grounds.