According to Bttttger, the simplest method of giving paper surfaces a crystalline coating is as follows: - Mix a very concentrated cold solution of salt with dextrine, and lay the thinnest possible coating of the fluid on the surface to be covered, by means of a broad soft brush. After drying, the surface has a beautiful bright mother-of-pearl coating, which, in consequence of the dextrine, adheres firmly. Prof. Bottger mentions the following salts as adapted to produce the most beautiful crystalline coating: - sulphate of magnesia, acetate of soda, and sulphate of tin. Paper must first be sized, otherwise it will absorb the fluid and prevent the formation of crystals on its surface. Visiting cards with a mother-of-pearl coating have for some time been in use. Coloured glass is well adapted for such a coating, which has a good effect when the light shines through.