Isinglass

Noun

1. A form of gelatine obtained from the air bladder of the sturgeon and certain other fish, used as an adhesive and as a clarifying agent for wine and beer.
2. A thin, transparent sheet of mica (probably from its similarity to true isinglass and/or resulting from confusion with the term Muscovy glass for glazing made from mica, but also used for isinglass, which was chiefly produced in the Caspian Sea region of Russia, or Muscovy).