"The bird and caterpillar molds are both gypsum ceramic molds that I found at a place called Urban Ore in Berkeley, where they basically go through junk yards, pick stuff out that people might care about, and sell it at ridiculously low prices. My particular molds were about 15 cents each, and made in the 70's. The caterpillar is 97% tin, 3% copper, burnished with some zinc on the outside via electrolysis."