Chemical clean

[sailn2ba]

I had my horn chemically cleaned. Was assured that they don't use acid for that., Immediately afterward the tuba felt really open and smooth. However, my rotary valves have started making a scraping sound (I usually lubricate them through the slides; down the middle to avoid grease). When I remove the backplate to lubricate the spindles directly, I see a blue-green deposit that says copper sulfate to me (copper oxide being black). Does the chemical cleaning use a formulation including sulfuric acid? Would a lot of extra rinsing help?

[Rick Denney]

I had my horn chemically cleaned. Was assured that they don't use acid for that., Immediately afterward the tuba felt really open and smooth. However, my rotary valves have started making a scraping sound (I usually lubricate them through the slides; down the middle to avoid grease). When I remove the backplate to lubricate the spindles directly, I see a blue-green deposit that says copper sulfate to me (copper oxide being black). Does the chemical cleaning use a formulation including sulfuric acid? Would a lot of extra rinsing help?

Most chem-cleans do use acid, though not sulfuric acid. The traditional cleaning bath was chromic acid, but I've also heard of oxalic acid and even acetic acid (as in vinegar). The way I learned it, the chem clean is a two-step chemical process--a degreasing detergent cleaning to get rid of the grease and slime, and then an acid dip to get rid of calcium deposits that cause dezincification. But an acid bath requires a very thorough rinse, and maybe the rinse wasn't quite as thorough as it needed to be.

How long has it been? Are you sure it is not calcium deposits you are seeing?

Rick "whose knowledge of chemistry is just about exhausted" Denney

[iiipopes]

And a tech friend of mine showed me the gallon jug of concentrate for his shop's ultrasonic bath, a buffered form of phosphoric acid.

[sailn2ba]

Thanks. Will check. Meantime, when I disassembled the valves, they were clean inside. The blue deposit was only in 2 of the bottom caps. The scratchy feel was due to dry spindles. When I lubricate them properly by sucking oil into both ends of the spindle with the slides, they smooth out. Putting oil down the slide just doesn't get it to the right place.

[sailn2ba]

Oh, and it has been 4 months since the chem clean. Pretty sure it's not calcium because of the color.