Hi guys! (First of all, sorry for my english)

I am worried a bit, because i bought my new shires q30yr trombone and i spotted a patch on the corner of the bell, and i can't decide it is a red rot or just the lacque ruins out.

https://files.fm/u/9vumxsqjc i upload a picture about this.

That's acid bleed. Harmelss, but annoying to look at

Oh thank you :) and how does this usually occur? because I took care of the instrument, I didn't take it outside in any extreme weather

Acid bleed is what happens when solder under the lacquer expands and spreads. There's not much you can do to prevent it because it happens kind of randomly. You can fix it post production by removing lacquer, buffing it out, and then relacquering but it's purely a cosmetic problem. You typically don't get it on unlacquered horns because the solder isn't trapped under the lacquer; likewise, you won't get it on an instrument with an unsoldered bell bead. But on instruments that are lacquered and have soldered bell beads it happens fairly commonly.

It's not the solder that causes the black marks. It's caused by flux trapped in the crease caused by the rolled bell rim. It's difficult and relatively expensive to remove so some lower end instruments shorten the clean time after soldering the bell rim so lower quality instruments will have this more often; but I have it on my Shires bell and on my Yamaha 682 trombone. The flux is acidic and causes an oxidation on the surface of the metal near the joint. It usually appears quickly but then stops growing and will remain stable for years.

[quote="BGuttman"]It's not the solder that causes the black marks. It's caused by flux trapped in the crease caused by the rolled bell rim. It's difficult and relatively expensive to remove so some lower end instruments shorten the clean time after soldering the bell rim so lower quality instruments will have this more often; but I have it on my Shires bell and on my Yamaha 682 trombone. The flux is acidic and causes an oxidation on the surface of the metal near the joint. It usually appears quickly but then stops growing and will remain stable for years.[/quote] I've got a bit of it on my Kanstul 1570, but it took years to appear. Also some on my Bach 42 and King 3b, also which took years to appear.

There were however 80s and 90s Yamahas which were known for developing acid bleed around the rim, sometimes all the way around. My high school band director / private teacher had a Yamaha YSL-691 that was that way.

Orban,

Welcome to TromboneChat. As noted, this (acid bleed at the bell rim bead) is very commonly seen, even in very high-quality trombones. It is unlikely to get any worse or spread.

Think of it as a sort of a birthmark or character indicator or tattoo for your trombone, and enjoy playing it!