This is made by boiling litharge, olive oil, and water together, over a slow fire, until they concrete into a plaster. According to the views now generally received, olive oil consists of two fatty acids, the oleic and margaric, combined with the oxide of a hypothetical radical denominated glyceryle. During the process, the oxide of lead unites with these acids, and the oxide of glyceryle takes an equivalent of water to form glycerin, which is in great measure separated by kneading under water. The plaster is, therefore, oleate and margarate of lead, probably with a little unseparated glycerin, which is useful by giving it more plasticity. As kept in the shops, it is in cylindrical rolls, of a grayish or yellowish-white colour deepening on exposure, brittle when cold, but softening and becoming adhesive by a very moderate heat.

This preparation is much employed as the basis of other plasters, but is also itself highly useful as a direct application to the skin. In excoriations and slight superficial wounds and sores, it promotes healing by its sedative property, and by protecting them from the air. To guard surfaces against friction and pressure, and thus to prevent bed-sores, it is one of the best applications that can be made. Surgeons sometimes employ it to keep the edges of wounds in contact, and for strapping the leg in ulcers of that part, when bandaging is employed in their treatment. For these purposes its freedom from all irritant properties peculiarly adapts it; but it is not sufficiently adhesive without some resinous addition, and should, therefore, be used only when the skin is peculiarly delicate. It may be spread on leather, linen, or muslin.