Posted by K on February 22, 2004 at 23:04:00:
In Reply to: Piston Valve Construction posted by Jay Bertolet on February 22, 2004 at 20:14:33:
I certainly understand your concern about an instrument of such immense value.
However something similar also is known to players of more humble instruments.
Joe S has long ago written on new piston instruments getting better when the inside of the piston casings corrodes and thereby fills the minuscule gaps between casing and piston, so that the instrument gets tighter. (The same happens on rotor valves, only here the rotors also corrode.
To understand what I think happened to your instrument, we have to enter a biological factor: tartar. Not the one on your teeth, but the portion of it which passes your embouchure, before it can settle on your teeth.
This calcium mixes with the corrosion while it builds inside the piston casings. There it might constitute a minor wear factor to the piston itself, but as long as the valves are well oiled and running well, then there should be no major problem.
Now you get the instrument cleaned with ultrasound, and that brings one of the main features of chalk to the foreground: its brittleness.
The corroded-brass-element prevents the layer containing calcium from flaking immediately, but the ultrasound creates cracks in the layer.
When you oil the pistons after the ultrasound cleaning, the oil will penetrate the cracks and to some degree run below the corrosin/calcium layer, which eventually will come loose.
When you say "But clearly you can see a small section in two of the casings where the metal is a different color than the majority of the casing interior. It almost looks white, like maybe the casing is made of solid silver and then plated with brass", then my explanation would be this one:
What looks like white silver is the original polished brass surface, which come out clean and very reflective, when the corrosin/calcium-mix flakes off. What looks like brass, is the corrosion layer, which has not flaked off yet.
My approach to the problem would be to oil generously with very thin oil for a period and wipe out the valve casings more often than usually. Also to rinse the springs and the bottom caps at the same time.
In the old days before the ultrasound equipment entered instrument workshops, the brittleness was on purpose created by letting the valve casings soak in benzine, which was applied with a drenched cloth (only to be used in very well ventilated rooms). After that the pistons were oiled with a heavier oil, activated, and again cleaned with benzine.
Whereafter normal playing and oiling could begin.
I would use the benzine procedure (without the heavy oil) until the flaking stops.
After that the corrosion will continue. The solution to the problem will be to diminish your calcium output.
I have had huge problems with calcium in the pistons of my British style compensating baritone. which has a very short leadpipe.
The problems diminished, when I became a toothbrushing freak. They diminished even more, when I stopped drinking milk due to an allergy.
Klaus