Metals have a dense, non-porous surface that is waterproof. This prevents oil based ink adhesion. To code metal, solvent based, wax based or UV-curable inks are therefore required. These inks bond to metal when their solvent evaporates, their wax solidifies by cooling, or when a flash from a UV light dries them. By far most coding on metal is done for internal production purposes or on location like for example welding jobs on construction sites.
Metal is most commonly coded during the production phase by Hi-Res Inkjet in combination with solvent based inks. Hi-Res Inkjet can also be used with UV-curable ink. Coding is done on the production line when the material is in motion, or by a traverse in static situations. For codes that do not vary much, economical options such as a Rollcoder or Hot Solid Inks can also be used. Finally, for manual coding on location also Markers are often used.