On Monday, October 24, 2016 at 5:13:02 PM UTC+2, Paul K. Dickman wrote:
"robobass" wrote in message
...
I make an unusual product (www.basscapos.com) which must be polished to
jewelry standards, but includes a 5/16-24 threaded brass stud which is
soldered to a brass bar. Torch soldering naturally produces firescale, which
is hard to remove from the threads. There is a very effective product to
combat this called Cupronil. You first preheat the work to maybe 600逆 and
then spray it on. It leaves a coating which protects the part. Works
wonderfully. Problem is, I am going through it like mad. I have tried a
bunch of different pump spray bottles, but none give me a nice focused spray
pattern so that I don't waste the bulk of it. It wouldn't be such a problem
if I could buy it in my country (Germany), but I can't. I suppose I should
invest in an airbrush. I have a compressor, but I like the simplicity of a
spray bottle, and the airbrush would still involve some experimentation to
get it right. Can anyone think of an application where a precise pump spray
bottle is used and easily available? Cupronil seems to be similar in
viscosity to water, but it is enough different that a bottle which gives a
perfect spray pattern with water isn't very good with Cupronil.

Thanks!

On a piece that size you should be able to dip.

In any event I wouldn't use it. Unlike sterling and white gold, the
firestain on brass isn't a deep oxide layer. It is simply a copper layer
left when you burned out the zinc in the alloy.

Do a web search for "Hydrogen peroxide pickle". I can be made up with 3%
drugstore peroxide and sparex (sodium bisulsate).

After pickling normally to remove flux and scale, a hot dip in the peroxide
mix will strip off the copper and leave you with a frosty brass finish. Use
a fine brass wire wheel to burnish the threads and polish the handle
normally.

Thanks all. Paul, I'm not so sure I agree with you, but I will try it. In the mean time I have invested in a cheap airbrush, which has absolutely solved my problem.