Raw Brass Chem Clean

[paulyg]

I got a raw brass horn back from a bath today and the unlacquered brass parts of it are pink. My understanding is that this is the result of zinc being dissolved from the brass. Is this practice common for chemical baths? I'm only slightly worried that the life of the horn has been shortened by this process...

[BGuttman]

There's a very thin layer of brass that is low in zinc.

You could polish it off, or learn to love it.

Unless you do chem cleans every week it's unlikely you will do much damage to the horn.

[mrdeacon]

Just polish it off like Bruce said and let the patina develop again. I just had my raw brass bass get an acid bath and in certain spots it's pretty funky. The seam on the bell is pink like you described. Planning on polishing it up next week.

[brassmedic]

Why do you think the "life has been shortened"? What do you think is going to happen?

[Bart]

We chem clean instruments all the time and we tested our chemicals by putting an already old piece of tuba tubing in a small bath with the pure chemicals. (As opposed to the much diluted version we use in our big bath.) The theory was that the chemicals would slowly eat away the zinc and the tubing would (at some point) start to fall apart. We left it in the pure bath (which we refreshed frequently) for over three years. And the tubing was still there. Alright, it was becoming a bit brittle at this point, but it was still there. And no instrument will be subjected to such an intense treatment. So we are not worried a bit about our chem cleaning. If your repair tech is competent, you shouldn't either.

We also experience that the colour change usually only happens on the pieces of brass where there was already a (calcium?) deposit. Although most instruments are lacquered or silver-plated, the insides of the tubes are usually bare brass. The parts that are clean usually stay yellowish in colour. The parts that have had some deposit on them turn more red or pink. I think that is due to the deposits already eating away some of the zinc. And that only shows when the deposits are removed.

One way to turn all bare brass to red: leave a bit of iron in the bath. We make sure we never have any iron even near the bath!

I'm not a chemical engineer, so my theory may be a bit off. But that is what we experience every time again.