cleaning brass/copper

Get some copper cleaner from the grocery store if you're determined to remove the patina. Then understand that keeping it shined up is like doing dishes. Bugs

Two things come to mind, if your black stuff is what I think it is (cupric oxide): pickling and tumbling. For me, typically both, and in that order:

I clean up lots of old brass and bronze items (pipe fittings included) in a warm pickling bath of sodium bisulfate (pool grade "ph Down") and hydrogen peroxide (also pool strength, eg "Baquacil"). This mixture is a slightly safer version of the industrial sulfuric acid and peroxide pickle. The sodium bisulfate solution without the peroxide will take away the black cupric oxide by itself, but you'll typically find that this leaves your part with some red cuprous oxide still on it, particularly if the part started out with a brown natural mix of the two oxides.The peroxide in the pickle will dissolve the red oxide. This mix will also attack the copper, so any pickle with peroxide in it has to be *carefully* watched--if the solution starts to go blue from copper sulfate formation, it's starting to etch the base metal.

After pickling, a brass or commerical bronze item with some zinc in it typically forms a whitish zinc oxide coating, due to the large zinc surface area exposed by the chemical cleaning. This is much more easily tumbled off than the copper oxides. A vibratory tumbling with corn cob or walnut shell media will give you nice, like-new pipe fittings. You can put some of your favorite brass polish in the mix too if you want them to really gleam.

-Adam

Here is an example for you, a red brass (85-5-5-5) boat horn which I gave the sulfuric-peroxide treatment to:

The pickling was preceeded by some Citristrip to get right of the white paint blobs, and followed by a liberal application of Baldor buffer to the shiny parts. Nevertheless, the chemicals did all of the work in getting rid of the tough chocolate coating, and also the spots of the various other copper salts (the green and blue areas). I could not have simply buffed right through the brown oxide layer because the cast brass is somewhat porous. I'd have been left with dark speckling from pits that still had the oxides (that or a very thin horn! :-)

-Adam

Impressive! Thanks a lot for your chemical baths. I have printed it out.

Nick

So, what's a good coating to use to preserve the shine? (Assuming it's gonna be a one-off job, where a big tank of lacquer dip isn't appropriate.) Is there a good clear spray that comes close to leaving a finish like what is found on, say, a trumpet?

Joe

I asked this same question in the musical instruments repair and builders groups, as I had a set of spun-brass ship horns that needed just such a treatment. I was told that the lacquering of brass instruments is something of an art form, with many of the amateur instrument builders frustrated by trying to get a perfect, drip-free, sag-free glossy clear finish. I've had the best luck with gloss Krylon "Lacquer" and no luck with the Krylon or Rust-oleum clear acrylic enamels (they have always given me a slightly hazy finish that kills the sharp specular highlights of the bare polished brass).

I don't think there are any lacquer dipping processes used, since that would be sag city, but I do suspect that a lot of the cheaper instruments, and perhaps even some good ones, are using a clear powdercoat now. Door knobs, handles, locks, lamps and other polished brass items are certainly powdercoated nowadays. Sears even sells a DIY clear powdercoating system, as to the major industrial supply places (Grainer, MSC, McM, etc).

If you do lacquer, it won't last forever. Outdoors it might not last long at all. Amongst boat owners, there are two schools of thought regarding exterior polished brass adornments: polish weekly versus lacquer and strip yearly. For my brass truck horns (from a tugboat), I chose the latter, and so far they've held a good coating outdoors for 6 months. By this time next year, I expect to have to strip them (acetone bath) and repolish, relacquer.

-Adam

How would one create that sort of chocolate brown patina? I like to make copper and brass tokens for my shop and would like to give them a nice dark brown, deep green or blue patina. Something more than just a light surface coating.

Kyle.

Hi Kyle.

Liver of sulfur seems to be the traditional method, at least for jewellery.

-- Jeff R.

There are all sorts of patination compounds available.

I've used NOVACAN Black Patina for Solder and Lead which darkens brass

- almost black.

- $3.56

The copper one can be used as well, and tends to be slightly greenish, but to get bright green you really need copper.

Th first on uses selenious and nitric acid. The second uses zinc cloride.

The brown forms naturally in air. Keeping the coins hot and in supply of oxygen would speed this up. Naturally formed patina is better and more durable than any chemical cheat, and you can have good results in a few weeks. Worth trying if you are patient.

Patination quick solutions:

Ferric nitrate will turn copper brown to orange, Liver of Sulfur will promote formation of the black oxide, and Copper nitrate will give you a green patina. I believe the green is usually lacquered over for durability. I've never tried any of these; my polished copper items turn brown so fast on their own I've never looked into speeding it up :-)

I would not think it desirable to have sulfate or carbonate formation on your coins (shades of green and blue you see on outdoor copper items, especially by the ocean), because these can rub off and are toxic.

-Adam