goldbeaters’ skin

Preferred label: 

Prepared outside membrane of the large intestine of cattle used primarily to separate individual gold leaves during the final stages of beating gold leaf.

AAT

The Arts and Architecture Thesaurus Online, The Getty Research Institute.

Additional reference: 
http://vocab.getty.edu/aat/300252173 (modified)
Broader concept: 
Top concept: 
materials
Getty AAT: