Goldbeater's skin
Goldbeater's skin is the processed outer membrane of the intestine of an animal, typically cattle, which is valued for its strength against tearing. The term derives from its traditional use as durable layers interleaved between sheets of gold stock during the process of making gold leaf by goldbeating, as a batch process producing many "leaves" at the same time. In the early modern production of airships, application of its high strength-to-weight ratio and reliability were crucial for building at least the largest examples. Manufacture 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 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. Applications Goldbeater's skin is used as the sensitive element in hygrometers, since its hygroscopic behavior includes contraction or expansion in response to