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Copper effect of ammonium chloride on hot brass




While doing some craft work I discovered that if clean brass is heated sufficiently, then dipped in ammonium chloride (sal ammoniac) solution, the brass acquires the appearance of copper. Presumably the tin in the alloy is removed at the metal's surface, but what chemistry is going on here? Are there toxicity hazards that need more than standard clean workshop habits?

Many thanks if you can answer.

Mick Pearce
hobbyist - Brampton, Cumbria, UK
2006



January 11, 2011

What you are doing is removing the Zinc from the Brass (Copper and Zinc) often in some acids and other reactive solutions the zinc is ripped out of the alloy structure.

The good news is that now that you have a nice coating of copper you can color the copper with other chemicals Liver of sulfur is one.

Hard part to get the brass finish back, I have to mechanically polish or steel wool the surface to remove the copper layer.

This also happens when one solders brass with too harsh of flux. The flux activates and rips the zinc out of the flux affected zone.

Paul Barnhart
barnhart studios - lake in the Hills, Illinois USA




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