Colored Varnish for Marking Glass

Q. Our factory uses pressure and temperature gages with glass covers to control our processes. I need to mark the safe work zone of the surface of gages so that our operators can easily tell when processes are within parameters. Markings must be made with a clear material that is a bright green color. Permanent markers and transparent stickers do not work because they can be removed by the high-pressure steam we use very often to clean our machines. Can I use some sort of clear lacquer to mark the zones? J.B.

A. Yes, you can use a colored clear lacquer for your markings, but a colored clear varnish would be better. Lacquers, in general, use thermoplastic resins as vehicles and may not be able to withstand the high-pressure steam cleaning. Varnishes, which have more robust vehicles, should be able to withstand the cleaning process. An epoxy-resin-based varnish colored using a green dye should work for your application.