Paint / Liquid for obscuring IC's? for marking tubes?

anyone know what the paint or liquid that companies use to obscure the model of their IC's? i usually see people using a silver type of paint or something that looks like the silver sharpie used for autographs.

on a similar note i'm also looking for the paint or liquid that's sometimes used to make notes on tubes for sorting. I've seen it in multiple colours but am wondering what the liquid is. something that's able to withstand heat. i'm thinking maybe some type of oil paint?

anyone have experience with this? thanks!

I've seen a lot of scratching for erasing part numbers from ICs. For the tubes I don't know, you also need it to stick to glass, high temp glass friendly is calling for epoxy or maybe silicon based, but I guess epoxy should be good enough for tube temps.

JS

I just use a black Sharpie for marking tubes.  Seems to survive the temps fine but is easy to clean off with isopropyl alcohol.