Isinglass

Webster's Dictionary

(1): ( n.) A popular name for mica, especially when in thin sheets.

(2): ( n.) A semitransparent, whitish, and very pure from of gelatin, chiefly prepared from the sounds or air bladders of various species of sturgeons (as the Acipenser huso) found in the of Western Russia. It used for making jellies, as a clarifier, etc. Cheaper forms of gelatin are not unfrequently so called. Called also fish glue.

The Nuttall Encyclopedia

A gelatine substance prepared from the sounds or air-bladders of certain fresh-water fishes, the sturgeon in particular; it is imported from Russia, Brazil, and the Hudson Bay Territory.