What exactly is “Isinglass”?
“Isinglass” (also spelled “eisenglass”) is often misunderstood as well as misspelled. Isinglass is a name that has been used for centuries to refer to thin sheets of the soft mineral “mica”, which was used as windows in houses & carriages, as well as naval ships of war. It let light in while being flexible enough to withstand damaging vibration or impact.