You can do this with electro-stripping, much easier and safer than
strong acids. This process is used all the time by welders and
fabricators on stainless steel. I’ve used it on jewelry with good
results. You need a DC power supply capable of a couple amps at 18-30
volts, you can even use 3 6-volt lantern batteries in series for
one-off jobs. Get the CitriSurf product described below, or make your
own strippiing solution as described.
There is a citric-acid based system called CitriSurf. Google for
their website. I’ve done small jobs with a home-brew of 10%
food-grade citric acid and 1% sodium EDTA dissolved in distilled
water. Basically the same stuff as the CitriSurf, except theirs
includes additives to make the solution gell some, so it doesn’t run
off vertical surfaces.
Warm the solution and use it to electro-strip at about 18-20 volts.
Works like a charm, the stains will just about wipe off. Wand is a
piece of copper tubing, flattened at the end with a piece of green 3M
cloth wire-tied around it. Rest of the wand is covered with heat
shrink to insulate it. The work is positive polarity, so the ions
come off the work, wand is negative.
The EDTA is a chelating agent that helps keep the stripped metal in
solution. You can buy it from chemical suppliers or on eBay.
You can passivate the stainless after electro-stripping by soaking
it in the same solution, heated to about 110 degrees F, for 15-20