What is isinglass?

isinglass sheet
   Isinglass is a particular pure, transparent form of animal gelatin. The material is much the same as that of fish scales. The supply of isinglass is obtained chiefly from the air bladders of certain fishes. Formerly the sturgeons of the Caspian and Black Seas were the main source of supply, but Brazil, and the East Indies now furnish apart of the isinglass of commerce. The name has been applied popularly but incorrectly to the thin sheets of mica used for the panels of coal stoves, which resembles isinglass in appearance only. Isinglass panels would burn out instantly. Isinglass dissolves readily in hot water. In cookery, it is used to make jellies, blancmange, and to thicken soup. Being akin to glue, it is used in the manufacture of certain cements and court plaster. It is employed as a sizing also to stiffen silks, gauze, and linen.