isinglass consists of collagen, which, when heated with water, yields a pure form of gelatin. Isinglass is obtained from the swimming bladder (also known as ‘sound’) of certain fish, especially the sturgeon (from which ‘Russian isinglass’ is obtained), but also a large catfish of S. America (yielding ‘Brazilian isinglass’), some species of Asian waters, and (in N. American waters) hake and cod.
The sounds, once removed from the fish and cleaned, are dried, and treated to acquire various shapes (e.g. ‘book’ when folded like the leaves of a book, ‘pipe’, ‘ribbon’).
