Both rust browning and rust bluing solutions are accelerated rusting solutions, and there are many formulas used for rusting barrels. It is the boiling step that converts the red oxide (ferric oxide) to a black oxide (ferro ferric oxide). The process is used on fluid steel barrels for bluing, but not with the addition of logwood chips, and of course, there is no etching step as is done with Damascus. You might find it easier to card if you do that after your boiling step.

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