I soldered up some mystery brass sheet stock I had lying around, to make rectangular-cross-section tubing for a scale model project, and I’ve been trying to do a DIY nickel plating process on the resulting parts (nickel acetate). Unfortunately, despite multiple attempts, the nickel plating comes out blotchy, dark or black in places, with patches of bare brass. Meanwhile, other bits of brass (shim stock and K&S tubing), copper wire, and even steel seem to electroplate just fine in the same bath- or at least a lot better than these brass bits I spent so much effort building.
I’ve tried: sanding everything back to bright metal; washing with acetone or mineral spirits; etching a bit with muriatic acid; and varying the voltage of my plating setup from ~3 to ~9 volts DC. I’m handling the parts with gloved hands. I’ve moved the nickel cathodes closer and farther away. I’ve agitated the bath to knock bubbles off the metal. I’m at a loss, and looking for fresh ideas.
Is it the fact that these parts are soldered and the others aren’t? Is it possible that the brass sheet stock has some innate contaminant? Do I need to clean the parts with a different solvent? The fact that other brass samples seem to plate OK makes me suspect the brass itself, but admittedly the parts that are failing are built from thicker stock and are larger overall than the test pieces.
Probably a different alloy composition that doesn’t play well with electroplating? Trace amounts of something (possibly even nickel?) that deters the plating process?
Have you tried plating a piece of the bare original sheet stock?
Progress, of a sort! I had a bit left, with a few solder flecks on it. I sanded it to bright metal, washed with soapy water followed by acetone, did an etch, and tried to plate it. The silvery solder marks immediately turned greyish black, and the rest of the metal didn’t plate. So I took the same piece and cut off a section that had no visible solder on it and repeated the process, and got a much better plating result, but still with odd grey splotches and whorls.
So now I guess I have reason to suspect both the solder and the metal itself - with solder visible, it seems to attract all the plating, and even without, there are still weird surface effects.
I think I’m going to have to remake the parts with a lead-free solder after pre-testing a new supply of brass stock.
If lead is the issue, it might be free-machining brass, that’s got quite a high lead content (vs K&S tubing which is a 260 cartridge brass. I imagine shim stock is similar)
I see that alloy 360 brass is 3% lead. Yeah, I’m going to start over with new material. I didn’t know that about the different brass alloys; thanks!
By the time I’ve remade all the parts I should have the process down pat!
