For a while now I've been using felt tip "metallic marker" pens for contrasty marking over black IC bodies. UK/ASDA own brand silver-colour and gold-colour work very well, but like all these they are broad tip only , so its a matter of sharpening the tip with a razor blade and using the very lightest of writing force. I've also been using them to write gains , test date etc on the bakelite skirts of valves/tubes. Today I wondered if they would survive hot glass envelopes of valves in use,. Tried marking some glass with the silver and gold and also a black permanent CD marker pen. Taking to 220 degree C the metallics surtvived fione but the CD marking degraded easily. Will have to see about long term use but worth a try
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on