I have been looking for a really good, permanent stamp ink and I have finally found it! I tried several that claimed to be suitable for all surfaces (such as vellum), but this is the only one that lived up to that! It comes in a wide variety of color selections as well, so that is an added bonus :) Good luck stamping!
This ink says it works on everything and it works on everything. I've used it on material, acrylic, metal and it stays on just like its' name.