Dichroic coated copper foil is 1/2 the cost of dichroic glass and the silver rainbow coating is three times as thick as regular dichroic coatings. It is non COE specific, so may be used on any glass type. No pre-heating is required - the coating jumps off the copper and attaches to molten glass when marvering. It is normal for the dichroic coating to flake off of the copper and be loose in the bag. Each piece is sealed in a static free bag so you can easily collect the flakes.