The residue of skin oils, salts and moisture left by touching a vacuum surface without gloves. In high vacuum and UHV a single print releases water and hydrocarbons long after pump-down, can cap the base pressure and contaminates sensitive surfaces, and a bake can carbonize it onto the steel. The rule is gloves for anything that goes inside, and a solvent wipe for any part that has been handled bare.
Who handled the shield without gloves, there's a fingerprint right on it, wipe it with IPA before it goes back in.
UHV people change gloves after touching their face or phone, because one touch can cost a day of pumping.
Also heard as
- finger oil
- skin oil
Related terms
Outgassing
Slow release of gas from the surfaces and bulk of materials inside a vacuum system.
Bake-out
Heating a vacuum system while pumping to drive off water and other adsorbed gas and lower the base pressure.
UHV
Ultra-high vacuum: pressures below about 10⁻⁷ mbar, reached only with baked, metal-sealed systems.