Goldbeater's skin

Goldbeater's skin is a sheet of tissue traditionally used in the process of making gold leaf by goldbeating. The skin consists of the processed outer membrane of an animal's intestine, typically an ox, and is interleaved with gold stock to facilitate batch production of many leaves at the same time.

To manufacture goldbeater's skin, the gut of oxen (or other cattle) is soaked in a dilute solution of potassium hydroxide, washed, stretched, beaten flat and thin, and treated chemically to prevent putrefaction. A pack of 1,000 pieces of goldbeater's skin requires the gut of about 400 oxen and is only one inch thick. Up to 120 sheets of gold laminated with goldbeater's skin can be beaten at the same time, since the skin is thin and elastic and does not tear under heavy goldbeating. The resultant thickness of gold leaf can be as small as 1 μm-thick.

Goldbeater's skin is used as the sensitive element in hygrometers, since, due to its hygroscopic property, variations in atmospheric humidity cause skin contraction or expansion. Alexander Graham Bell used a drum of goldbeater's skin with an armature of magnetised iron attached to its middle as a sound receiver (see Invention of the telephone), and the North German Confederation printed 10- and 30-groschen postage stamps on goldbeater's skin to prevent reuse of these high-value stamps. Joseph Thomas Clover invented an apparatus for the inhalation of chloroform in 1862 that consisted of a large reservoir bag lined with goldbeater's skin to make it airtight, into which a known volume of liquid chloroform was injected. Due to its transparency, strength, and fairly uniform thickness, goldbeater's skin is also used to repair holes and tears in manuscripts written on vellum.

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