Electrochemical marking, also called Electromarking, is a fast, efficient way to mark metal permanently without distortion. It's permanent because you make the Electromark by etching out metal, then plating a stable compound of the base metal on the etched surface. Since in most cases the stable compound is an oxide, the Electromark withstands corrosion. We can prove this resistance to corrosion by the extreme length of time the Electromarking will stand up in a salt spray test.
The Electromark is a deposit into an etch approximately one ten-thousandth of an inch deep, yet it's produced in less than a second. The Electromark can be removed by abrasion, but the etch remains until one ten-thousandth of an inch of the metal has been removed.
The generally dark color of the Electromark's impression varies, mainly because of the difference in base metals. For example, some stainless steels yield a brown mark, whereas the mark in monel metal is jet black. Most dark marks are done with AC current.