Glass decals are made from soft glass milled very fine, mixed with a carrier oil, and silkscreened onto a backing paper. They are water-floated onto the glassware before the annealing process and fired on, at which point they become virtually permanent. There is a range of firing temperatures depending on the decal composition. They are in wide use by all scientific glassblowers and have several useful applications, such as frit porosity and joint size designations, scales, level marks, and making the origin of the glass easily identifiable with a logo. Custom decals are not horrendously expensive if you need a reasonably large number; for one-off or short runs, the set-up charge will run the price up. They require camera-ready artwork.