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I have a surface condition on an old tuba that sort of has me mystified. There are LOTS of spot on this horn that range from perhaps 1/32" diameter up to 1/4" diameter. It's not coming from the inside out... therefore eliminating the dreaded 'red rot'. In fact... there are spots on the bell on one side but not the other. This horn was covered with a greasy, very black substance when I got it that was a bear to get off. Silver plating will raise like this if it gets too hot. However, the solder joints are all OK... pretty much eliminating the idea of being in a fire. Any ideas what's going on? Here are some images:

Northernlb wrote:My first two thoughts are either one two many summers in the attatic or some kind or pitting due to some kind of chemical reaction.

I thought at first it was red rot. However... those spots are even on the bell and I can see that there is no corrosion on the backside. The silver is just raised.

Then... I considered a fire but if it was... it never got to 450F or so to melt the solder.

It could be chemical. But what???

????

[quote="YORK-aholic".....Distin or Keefer perhaps? ...[/quote]

Keefer. The bow guards are fully engraved, too!

Looks like it was sprayed with something. Maybe like a naval jelly or other stripping agent????

Dan, I would speculate (wildly) on hydrogen embrittlement due either to chemical (pickling) or to electrical variations. The embrittlement would be in the copper substrate.

See http://www.finishing.com/114/78.shtml" target="_blank" target="_blank

It also could be simply from an unclean brass surface.

Based on my experience with a lot of old plated instruments, I would suspect that there was inadequate, clean prep and/or problems with the plating bath. And contamination or depletion can cause this.

Another possible cause is using too high amperage/voltage in the strike phase causing bubbles to be present on the surface resulting in poor adherence. This is especially true if agitation is not used. Modern plating methods largely eliminate these problems.
Dan Oberloh could be the guru here.
My advice is to be conservative about attacking it as plating could start pealing once the surface is broken.

It appars to be a failure of the bond that has blistered; probably has been an issur going back to day one. Because of its age, it has probably developed into under plate corrosion that can be a serious problem. Been there myself with a few past old horn restoration.

Daniel C. Oberloh
Oberloh Woodwind and Brass Works
http://www.oberloh.com" target="_blank

tstryk wrote:So do we get to see the whole horn?

I had to get the horn cleaned up a little to even see where the dents were! The horn was covered with a greasy, black schmutz. It looked sort of like baked-on Cosmoline. You can't see in the picture. But... the bow guards are also fully engraved. I don't think any of the engraving was done by hand, though. .... more like it was rolled into the brass while it was still flat (before forming).

Here you go:

tstryk wrote:Where in the world do you find these great old horns?? I love that one.

It's a customer's horn. The fingerbuttons Joe alluded to are long-gone.

I'm not a repair guy,
But my Keefer sousa has similar little marks
in the silver plating like that.