Common Plaster.
Take of common olive oil, six pints; litharge reduced to a fine powder, two pounds and a half. Boil the litharge and oil together over a gentle fire, continually stirring them, and keeping always about half a gallon of water in the vessel: after they have boiled about three hours, a little of the plaster may be taken out and put into cold water, to try if it be of a proper consistence: when that is the case, the whole may be suffered to cool, and the water well pressed out of it with the hands.
This plaster is generally applied in slight wounds and excoriations of the skin. It keeps the part soft and warm, and defends it from the air, which is all that is necessary in such cases. Its principal use, however, is to serve as a basis for other plasters.
William Buchan
Domestic Medicine 2nd edition 1785