Isinglass

Isinglass is a semi-transparent, whitish substance, and is essentially an extremely pure form of gelatin. Initally it was produced by cleaning and drying the air bladders of the sturgeon, although it is now also obtained from cod, hake and other fish. After removal the bladders are cut open, soaked in water and rubbed to remove the outer membrane before being allowed to dry.

Isinglass is extremely useful as a fining agent when beer or winemaking, and will quickly clarify a stubbornly cloudy wine. It also has uses in the manufacture of fish glue, court plaster, stiffening jellies and in the creation of handmade paper. In recent years its use has greatly diminished, however, due to the rise in use of gelatin and other synthetic materials.

The name isinglass is also commonly applied to a gelatinous substance obtained from certain seaweeds, and also to a range of minerals that consist of hydrous silicates of aluminium or potassium. Such minerals crystallise in forms that allow them to split perfectly into very thin leaves. There is considerable variation in composition and colour, which can range from pale brown or yellow to green or black. Transparent forms were of considerable use in lanterns, stove doors and so on, though their use has long since been replaced by artificial alternatives.