I is for isinglass

...except that isinglass is a substance taken from the swimbladders of fish, particularly the sturgeon, and used in desserts such as blancmange.

Eisenglass is what a geologist call mica - more specifically muscovite - a mineral found in igneous or metamorphic rocks. The best way to identify mica is by its thin sheets that can be cleaved off. It's transparent, flexible, and has the general appearance of clear to cloudy plastic, but it's much harder and won't melt, hence its use in high-temerature applications such as stoves and lamps. Mica is still available and in use as insulators in electrical equipment, stove windows and lighting fixtures. It cuts fairly easily with a utility knife.

Henry Quiner and family lived near the Etta Mine, located in 1883 as a mica mine just south of present-day Keystone, South Dakota.
- posted by pioneergirl at 1:12 PM