More properly known as muscovite, isinglass is a form of mica that is often found in sheets. The sheets tend to be very thin and somewhat elastic in nature. Russia and India have been the site of mining sheets of mica on an ongoing basis. Isinglass is a mineral that can be found in a number of different natural formations, including granites and gneisses. The designation of muscovite for isinglass originates from the common usage of the mineral in the country of Russia. Around the city of Moscow, isinglass is often used for window glass. The particular formula that is used to create these clear and tinted panes of glass is known as Muscovy-glass. Isinglass is understood to form through a process that over time involves the natural alteration of various minerals until the result is the thin layers that can be mined and used for several different product types. Such minerals as kyanite, feldspar and topaz are often cited as building blocks for the creation of isinglass. Once the mineral
It is a substance derived from fish that is used to filter some alcohols, particularly wines. They don’t actually leave the isinglass in the alcohol, they just use it in the filtering process. So a regular old vegetarian could drink alcohol filtered with isinglass, but a stricter vegan would probably avoid it as much as possible. Since it is used as a filtering agent, and not as an ingredient, it’s not listed on ingredient labels. So the only way to be sure is (1) to contact the wine manufacturer and ask, or (2) to only buy wines that specificially brag about being unfiltered.