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I have some brassware with nice engraved designs that I'd like to bring out. If it were silver or gold, I'd use niello, but that apparently doesn't work on brass. I could try and do something to oxidise the whole surface and polish the oxidation off of the high points of the engraving, but ideally I'd like something darker.

I can see from pieces like this:

Engraved lamp stand Engraved lamp stand from the Met Museum, public domain

that such a finish is achievable, but the entry just lists it as

Brass; cast, engraved, and inlaid with black compound

So, what is the equivalent to niello which can be used to selectively darken recessed areas of a brass object?

I'd prefer more traditional methods, as opposed to simply spray painting the whole thing black and rubbing it off the high points, if possible.

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I think you will have to age the alloy first, and clean the higher areas afterwards.

For tarnishing, you can use Palmolive, or any kind of washing liquid that has sulphates in it.
Another, more aggressive option, but only viable for solid, thick brass objects, is to use ammonia.
The most traditional choice, however, would be to use a mixture of salt and vinegar.

In all cases, you can leave the brass object in the liquid for an extended period of time, or rub it in with a piece of cloth, which will give you more control.
After the tarnishing, you can use either ketchup, a mixture of vinegar, salt and flour, lemon juice, or soap, to brighten the brass again.

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The only thing that comes to mind is the application of asphaltum or bitumen of the type used to prepare a hard ground for etching. If you do it quickly and burnish off the raised areas, you should get something like niello...

  • Wouldn't this always be rubbing off, as well as running and staying sticky if it gets too warm? – rebusB Aug 29 '18 at 15:57
  • Well, the epoxide type of etching ground really only comes off with a solvent, and asphaltum / bitumen is probably as good as the ancients could have managed, and much better than waiting 1000 years for pollution to do its job. With modern techniques I would probably go with dip with a 2k and surface buff, but OP asked for traditional methods. – Nothingismagick Aug 29 '18 at 16:04
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    I see now that the museum calls it an inlaid compound; would have thought it was a chemically induced oxidizing process... like you just said! They could have done it back in the day as the chemicals are not that exotic and they were firing the metals to make pieces so high heat would not be a problem. – rebusB Aug 29 '18 at 16:16

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