Posted by bloke on February 22, 2004 at 22:14:18:
In Reply to: Piston Valve Construction posted by Jay Bertolet on February 22, 2004 at 20:14:33:
There may be some residual silver plating (whether or not well-adhered) in the casings from the "appearance" (exterior) silver plating job on the tuba.
Usually, final lapping removes any of this...but not always, and ultrasound may just be the thing to knock some of that stuff loose - whether or not that is a desired end result.