It's what they used to use before vinyl was invented, it's made from the silac beetle or something similar i cant quite remember, but it doesnt last very long and was easy to break, Thats what i think i remember from watching geeky music shows all the time!!!
nah..
as i said before, its what they use to cut the piece of vinyl, like a master if you get my drift, iv had some records pressed and i have the dub plates still...