The gold-beaters use three kinds of membranes, viz. for the outside cover common parchment, made of sheepskins, is used; for interlaying with the gold, first the smoothest and closest vellum, made of calves' skin; and afterwards the much finer skins of ox-gut, stript off from the large straight gut slit open, curiously prepared for the express purpose, and hence called gold-beaters' skin. According to Dr. Lewis, the preparation of these last is a distinct business, practised only by two or three persons in the kingdom. The general process is supposed to consist in applying them one upon another, by the smooth sides, in a moist state, in which they readily cohere and unite inseparably, stretching them very carefully on a frame, scraping off the fat and rough matter, so as to leave only the fine exterior membrane of the intestine, at the same time beating them between double leaves of paper, to force out what grease may remain in them, and then drying and pressing them. Not withstanding the vast extent to which gold is beaten between these skins, and the great tenacity of the skins themselves, they yet sustain continual repetitions of the process for several months, without appearing to extend or grow thinner.