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I do own a brass instrument (a trombone). The lacquer is damaged. I asked how to deal with it here.

Now I learned that the brass contains zinc, and there is a corrosion process called "dezincification". Now they told me to ask here how to identify real dezincificated parts. Here are the pictures:

Main slide handle:

Main Slide Handle

Bell "middle" section:

Bell middle Section

Bell inner rim:

Bell rim / inner

The issue is: On trombones (other brass instruments) red rot (dezincification) usually only appears on parts where saliva touches the instrument, i.e. in the front parts. On a trombone that would be the slide. So it is kind of unlikely but not unheard of that this might be "red rot" or dezincified.

It might also just be lacquer which went off due to improper handling (like not cleaning water spots, showering/cleaning the trombone with way too hot water, etc.).

Actual questions

  • How do I identify dezincifiaction correctly? Can it be seen on those pictures? (most important question)
  • What do you think of chemical cleaning? It sounds dangerous to me. Isn’t it going to damage the instrument?
  • What do you think of cleaning such an instrument soap? Is this going to damage the lacquer or material?
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  • $\begingroup$ I don't know enough to give a full answer but: 1. the cork barrel wear is lacquer only, 2. chemical cleaning should be safe, 3. the "shower technique" wouldn't cause this. The answer on the music post is excellent and should be followed. Find a reputable brass instrument (repair) shop, not just a music store, and talk to them. You probably don't need soap unless you delacquer the horn. IIRC lacquer on pro horns can be quite thin. $\endgroup$ – pentavalentcarbon Nov 8 '17 at 16:49
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Brass Instrument: Dezincification or just scrubbed off?

How do I identify dezincifiaction correctly? Can it be seen on those pictures? (most important question)

Instruments are made from solid brass, this is required as a stiffer metal like brass is required to have good sound quality. Your brass was not scraped off and the spots are indeed a result of dezincification. Water could get here for a number of reasons from fog mist to moist hands, it does not have to be saliva only.

What do you think of chemical cleaning? It sounds dangerous to me. Isn’t it going to damage the instrument?

From what I can find chemical cleaning looks like they use a mild acid and chelatior (like citric acid or EDTA) to etch away some of the red rot. However the brass still has to be polished and the lacquer needs to be reapplied.

What do you think of cleaning such an instrument soap? Is this going to damage the lacquer or material?

Soap won't damage the lacquer, but scrubbing might. That said your red rot shows that the lacquer is already damaged to you might as well scrub/polish the spots and reapply lacquer.

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It sure looks like dezincification to me. I have seen several cases in petrochemical service. It is fairly difficult to reproduce in realistic tests ( without unusual chemicals). It is surprising to see it in such ordinary environment. Zinc has been removed, so copper needs to be removed until you get down to unaltered brass . No easy chemical way to do this; grind,sand, buff, polish to restore the color ( then lacquer). It may not be worth the time or maybe there are instrument restorers that can do it. Try a few spots to determine how much work ( depth ) is needed. ............ If the manufacturer had used Inhibited Admiralty Brass ( 69 Cu : 30 Zn ,1 Sn , trace of As ) this would not have happened. They used Cartridge Brass ( 70 Cu : 30 Zn). Possibly it is a 60 Cu : 40 Zn brass , where again it would have been prevented with 1 % Sn. I am guessing more knowledgeable manufacturers use Admiralty or Navel Brass to prevent dezincification.

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