Re-labelling valves...

[Valvebloke]

I've seen the machine used by a commercial provider for doing this job. It was a simple roller-transfer arrangement with the ink (he did use the word ink) picked up from a small relief master (this was flat, as I recall) onto a roller and then off that roller and onto the valve. He said that finding inks which a) transferred cleanly, b) stuck well to glass and c) retained their colour given the high temperature that the valve would run at was difficult. He was sourcing some colours from a specialist supplier in Japan. I believe it's also the case that relatively new glass is much easier to stick to than old. As it ages the surface of glass changes, becoming both less chemically reactive and less physically stable, both of which make robust labelling more difficult.

VB