I continue to refer to this valuable resource. When I get a camera I want to do a post showing all the ways HotWire bulbs can fail. I have some with pretty slate blue on the interior of the lamp. I'm guessing that's evaporated titanium. I have some with white powder from slow burns and some that exploded that have a chartruese powder. I'm thinking these are gas combinations that are dicated by the type failure that takes place.