If that is what you mean, a small strip of metal cleaning/polishing cloth should work, followed by a cleaning with 91%+ alcohol.
+1
If the tubes are small signal tubes, take care cleaning the pins if gold plated.
FYI, I remember reading a thread years ago on AA about the steel pins on small signal tubes. Someone posted saying, the pins are not actually made of steel. Darned, if I can remember what it is though.
The reason given for not being steel. Steel will expand when heated. Not good when the tube is made of glass.
EDIT:
Quick search on the Net.
The metal pins on small signal vacuum tubes, also known as lead-out wires, are typically made of a ferrous metal, and the seals through the glass are made of a copper alloy called dumet..
"Dumet" refers to a glass-to-metal sealing alloy, specifically a bimetal made of a nickel-iron core encased in an oxygen-free-high-conductivity (OFHC) copper sheath, used for creating vacuum-tight seals in applications like lamps, diodes, and capacitor slug leads.
.
I’ll check the pins with a magnet...