I would like to put my two cents worth in and share my academic (
Watchmaking School, Machine Shops ) and professional advice on the
care and cleaning of files. When buying the file for the first time,
‘break’ in a file by filing over a piece of brass to remove any left
over post production materials such as micro-sized bits of steel.
To clean it, use a brass wire brush, not steel. Very soft steel wire
brushes are fine, however, they tend to be environmentally
sensitive, that is, they tend to rust or corrode. They are also of
magnetic nature and can contaminate your work. So brass is the way
to go. If cleaning when exposed to water, acids (not recommended)
and an ultrasonic cleaner, use a steamer or hot dryer/ heat gun to
remove any traces of water. Then use chalk to coat and protect when
not in use.