What could have caused this?

[Amconk]

My Holton has this one short section on the F-trigger tubing that the lacquer is severely discolored and darkened. It’s a bit splotchy. It almost looks burned, but as far as I can tell, there’s been no solder work near that spot, and it doesn’t have the typical texture of burned lacquer, it’s still shiny and smooth. Acid bleed of some kind? Part of me is tempted to buff the lacquer off of that spot and just shine it occasionally, or shoot a little spray lacquer over it once it’s cleaned. The other part of me just thinks leave it alone.

What do you think?

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[Neo Bri]

Could it be some material from a case or something having a reaction?

[Burgerbob]

I swear I've seen on a horn before, but apparently not on anything I own at the moment.

[MStarke]

My Conn 112h has some spots that look a bit like that.
No idea where it's coming from, but I don't think it has any impact.

I took the lacquer of the tuning slides and polished them which made most of it disappear.

[JCBone]

I have this all around the rim of my bach 42. I always thought it was acid bleed.

[Crazy4Tbone86]

It is caused by two things: 1. Pinholes or cracks in the lacquer. Sulfides and other contaminates in the air (usually slightly acidic) get under the lacquer and react/discolor the metal. 2. Improper cleaning/degreasing of the metal before lacquering. Essentially, the surface had some moisture or something on it that was (again) slightly acidic and it got trapped under the lacquer.....a form of acid bleed.

It can be buffed and touch-up lacquer can be applied. As long as it is cleaned/degreased, the touch-up lacquer should hold for at least a couple years, especially on a place that gets very little contact with your hands.

The question is....how pretty do you want your horn to look? If it bothers you, get it buffed and covered up with touch-up lacquer. Even with touch-up lacquer, you will see a color difference (the touch-up area will be a lighter yellow than the aged lacquer)....but it definitely will not be as pronounced as it is now.

[Amconk]

I’m honestly fine with it, as long as the metal isn’t compromised underneath.