Cleaning a steel ruler

Demo in real time

[@Theopheus]

Yeah, man, I thought this was gonna be a video about how to safely clean the ruler without removing the etching, but both a razor blade and metal polish are abrasive. This is not a good method.

[@apprenticemath]

Correct, also cleaners are either abrasive (Magic erases, Vim, toothpaste) or solvents (dissolve the black dye)