Take steel , q-tip , acid etchtant , gun blue.
Do it outdoors so you dont breath the fumes.
Dab on etch with q-tip ( thouroughly clean steel first of fingerprints etc) let sit for a few seconds , dab on gun blue, try to make the finish as even as possible , may have to repeat process.
Spray with windex to nuetralize acid , rinse , dry , oil to cure overnight.
You will have a colored finish but it will wear off or scratch off in time.