This is an electrolysis project using a 1960 industrial engineering book that tells how this is done. I need to make several spring steel valves that are no long available. Machine shops want $85 to $120 per hour labor. I can buy .010" spring steel in 6"x24" sheets $15 enough to make 50 spring steel valves. If I use paint to paint the shape of the valve I can eat away all the unpainted metal then remove the paint with paint stripper and have a valve which would have cost $10 about 25 years ago when you could still buy them.
I need to buy a titanium plate, anything thin will work, 1/16" thick x 8" x 12" is $20. The titanium plate is connected to the power supply, the spring steel is connected to the power supply, both are put in a salt water bath and 20 minutes later the metal that is not painted is gone.
With out looking at the book again I don't recall which plate is + or -.
The book says, best results is 3 volts. It also say best results is .5 amps per square inch of the titanium plate. Titanium has to be used to not contaminate the salt water mix with other metals. The water has to contain 4% salt.
Back in the days when this process was used, laser cutters had not been invented yet, no water jet cutters and no plasma cutters either, they had to find other ways to do things.