Tom Andrews, age 13, of Dayton, Ohio, for his question:

WHAT EXACTLY IS ISINGLASS?

Sometimes the partly transparent sheets used in the panels of stove doors are incorrectly called isinglass. Actually, they are made of the material mica.

Isinglass is the purest form of animal gelatin. It is used in the making of certain cements, jams, jellies and soups.

Isinglass is a tough, semitransparent substance which is prepared from the air bladders of certain fish. The best quality isinglass comes from the Russian sturgeon, but it may also come from cod, hake and other kinds of fish.

To prepare isinglass, the bladder is taken from the fish and washed in cold water. Then the black outer skin is removed and the remaining part is washed again and spread on a board to dry. Next the inner skin is taken out by rubbing and beating.

Next the bladder passes between rollers which reduce it to a thin, partly transparent ribbon which looks a little like watered silk.