Mica (also known as Isinglass) is a transparent mineral used as "viewing glass" in older antique wood and coal stoves. It has the appearance of clear plastic or cellophane yet withstands temperature of 1800° F. Because it is a naturally occurring mineral, several smaller pieces cost less than one larger one. This type of material can be cut with scissors, a razor blade, or a paper cutter to the size that you need.