For the chemists out there: sulphate process electroplating contaminants?

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So I'm doing some electroplating. I'm trying to purify some copper that is currently in the form of copper and brass bullet jackets. I melted the lead out of the jackets and sold that as scrap but there is a little bit of lead still there. There might be a few steel jacks there as well.

Anyway, I've got a bucket with the jackets in it, I added sulphuric acid and diluted it with water. I expected to get some hints of blue from copper sulphate but got nothing. None the less I set up a piece of copper pipe as my cathode and switched on the power. It draws about 150mA at 3.5V.

I left it for an hour or so, came back, and found I had some sort of black coloured plating on the cathode instead of copper. Does anyone have any idea what it could be? My best bet for contaminants are iron, lead, or zinc. Once the contaminant is depleted will the next easiest (lowest energy?) element plate out?