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Unsuccessful oxidizing of red brass for oil rubbed bronze finish

We do an "oil rubbed bronze" finish on sand cast red brass hardware. Our alloy is 83450 (a lower lead alloy) with 87 -89% copper. We pretreat using Phosclean Plus with 5% sulfuric acid at 140 degrees F. To oxidize, we are using TriS Chemical's Tribrown 444 new at room temperature. Some of our parts have a surface finish ground with a 120 grit belt and a Scotch Brite wheel to a satin finish. Some are oxidized as tumbled castings. After oxidation, the parts are rubbed with oil and wiped. We were successful with this finish for about six months then suddenly, we can't get anything to oxidize. The only way to get the color to take is to sand blast which, for most of our parts, is not acceptable. I would appreciate input from anyone who might have experience with this type of problem because we are mystified. Nothing seems to have changed.

Thanks.

Debbie Flood
- Grapevine, Texas
2004

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What does your sales rep for the oxidizer say? Have you dumped the bath and made it up new? I'd be somewhat suspicious of the lead content in your casting though. Lead doesn't will accept the oxidation like the brass will so perhaps your alloy has changed? I'd go back to the manufacturer of the sales rep and see what they say about the problem. If you're buying a proprietary process you deserve some support.

Daryl Spindler, CEF
decorative nickel-chrome plating - Greenbrier, Tennessee
2004