If you'r referring to titanium cylinders, be very careful.
Lots of threads on this subject,
Anything abrasive, your pencil eraser included, may damage the coating, leading to possible erosion.
I have two S&Ws with titanium cylinders.
They get soaked with MPro7, scrub with nothing more aggressive than a soft toothbrush.
Some stains remain. They do no harm. Trying to remove them may lead to coating damage.

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-jwk-
US Army '72-'95