A funny thing happened to Tim's LEDs while attempting to cast them in resin - For a project at work I had to mold some things in this hard clear polyurethane, so my Mechie ordered a giant kit of the stuff - more than the project ever will need (and it has a very limited shelf life). So I mixed up a little more than necessary and used the leftover to pot some LEDs. After some unsavory reaction in a plastic mold tray, he left the resulting mutant to hang dry for a few days. After finally hardening, he found himself the proud owner of the specimens seen above. - Playing with polyurethane casting material [via Ladyada's ranting]
http://blog.makezine.com/archive/2008/05/led_stalactites.html