Evil Mad Scientist Laboratories came up with a great idea for making coasters: photolithographic masks.
Photolithographic masks, or photomasks are clear templates used in semiconductor manufacturing. Typically, they are made of UV-grade fused silica and have a highly intricate chrome metal film pattern on one side. These remarkable objects are exactly the sort of wonderful thing that occasionally pops up at good electronics surplus stores. We recently found a few, took some pictures (see below) and, in the spirit of re-use, made them into some classy coasters.