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Starting another thread on raw brass and raw brass treatment, I didn't find one like this. I like some aspects of raw brass but like many of us am not a big fan of the in between or mixture, part shine, part tarnish. I've been thinking that black inner tubing with some polished brass accents would look cool (and maybe keep the bell area polished brass).

There are a variety of solutions that will develop a black brass oxide. For reasons of dezincification, we can assume alkali (like ammonia) based ones are bad. What about acid based blackening treatments. Anyone tried them? Are they durable? Any down side anyone can think of?

Back in the old days I believe they would tarnish items purposely with more concentrated excretions.

Currently though, I'm not sure what the best way to go about it would be. Black brass was a very popular finish for military hardware back in the first half of the 20th century. It's relatively durable, but I do not know what process they used back then. Probably something that requires a hazmat suit these days.

I was thinking of using something like this:
https://www.mcmaster.com/tool-black" target="_blank" target="_blank

It is an acid based mixture containing copper, nickel and selenium. Yes, it is highly toxic if ingested so if I do this, it will be done outside wearing good quality chem resistant gloves and a face shield. It is similar to compound used for steel and gun bluing. I am a technical guy in my regular job so handling chemicals is something I do on a regular basis though I generally avoid stuff quite this nasty but have handled far worse in the past.

I may try it on some scrap brass parts and see what happens. I would think it would passivate the brass surface but who knows. And per Bloke's comment, the idea is to do this on some of the smaller tubing in the hard to clean and polish areas (that turn ugly colors) so lack of uniformity should not be an issue. I do not intend to attempt blackening a bell for instance.

I don't know if this helps but I saw a video where they "aged" a trumpet
https://youtu.be/nRf8jqhXYTo" target="_blank
On their website, they used this procces to the point of an instrument being black
https://dequelery.nl/atelier/atelier-on ... nstrument/" target="_blank

I don't know if this helps but I saw a video where they "aged" a trumpet
https://youtu.be/nRf8jqhXYTo" target="_blank" target="_blank
On their website, they used this procces to the point of an instrument being black
https://dequelery.nl/atelier/atelier-on" target="_blank" target="_blank ... nstrument/

That was really interesting, thank you! The second one was great once I found the English button. My Dutch is quite poor. I only know a few words.
Hmm, I like the look better than green and other multicolored brass. Seems like polishing and cleaning/degreasing well is key to getting a nice uniform result. Also looks like time in the solution is important so that could be a challenge on a tuba since I don't intend to buy enough to dunk it. Plus, I wouldn't want the stuff inside the valves-seems like a recipe for disaster. I may buy a quart from here, https://jaxchemical.com/product-category/blackeners/" target="_blank" target="_blank, and give it a try on some scrap cartridge brass, that will be close enough to typical tuba brass for the experiment. I think the look of black small tubing with some polished brass accents and a polished outer tube and bell would look cool. Plus, keeping the bell and outer branches polished is pretty easy. I will definitely do some experiments first though on some cartridge brass tubing. If it works, I will report back with a photo or two.

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