Those who paint will know that wet paint comes off easy with a thumb wipe than a press with a pointy object. Dry paint however, may flake off with a pointy object, fingers do less damage.
All that is needed is to to wipe your finger on the button; does it feel oily and stained? Press with your key; does it feel oily at the end of contact?
Pressing with a key is less damaging to a wet coating than a finger press. Pressing with a key is more damaging on a dry coating than a wet coating.
It is a wet coating. Don't touch the buttons with your bare fingers.
Brass is less damaging on steel. Steel will scratch brass. This is one of the reasons the Mongols won, they had steel.
