Whatever process Andy of VTS uses - those are the cleanest non-gold-plated NOS tube pins I've ever seen. The dull gold plated pin tubes (e.g. premium 6922) seem to stay a lot cleaner over time.
I've heard of folks using CLR (carefully), but haven't tried it myself.
Cleaning tube pins
Anyone have any suggestions for cleaning gold plated tube pins on NOS tubes. I have heard that Caig's is not the answer. Plus, I do not want to take the chance of removing the gold plating.