Hi all- As a rank beginner, I have what I hope is an easy question:
what should I expect with I use borax flux when silver soldering
brass? After pickling, what I had was a copper colored “stain” on the
surfaces that were fluxed. My instructor told me that the flux had
"brought the copper in the brass to the surface." Should I have
expected this to happen? Was what really happened that the zinc in the
brass was evaporated or oxidized during soldering and I was left with
a thin copper-rich area on the surface? If this is to be expected, do
I have any flux options that won’t cause this (if I wanted a copper
colored surface, I’d be using copper…)
I use a hydroxide pickle after soldering brass and bronze, to get rid
of the copper surface. I don’t know of a flux that prevents it from
happening, though I’d sure like to! Sometimes the peroxide flux
caused some pitting on the surface; I’ve noticed this with a cheap
imported brass thing I tweaked. So be careful.
I got the recipe for the H2O2 pickle by doing a search of the orchid
archives.
You are more correct here than your instructor, at least in
describing what has happened. The zinc has been leached out of the
area where you were soldering. There really isn’t anything to be
done about it except to minimize the process by coating the article
in a solution of denatured alcohol and boric acid powder (a saturate
solution) to minimize the exposure of the heated metal to oxygen.
Look in the orchid archives for some of the formulae for “pripp’s
flux”. You will have to use physical abraision, i.e., polishing,
sanding, etc., to remove the discoloration so consider this in your
design. Also, you might try pickling the entire article (try it on a
sample piece first) in a heated sparex solution with equal parts
hydrogen peroxide added. Does anyone out there know of a way to
electro-strip brass?
I thought that it was the pickle that depleted the zinc in the brass,
not the borax. If this is true, does anyone know if one of the
alternatives to pickle (citric acid or vinegar+salt) would have the
same problem? Jade @Jade
I don’t know the chemistry involved, but I do know that when I solder
a brass or bronze piece, it usually comes off the heat with the
copper film, and the pickle doesn’t touch it. So I’m assuming it’s
the heat that depletes the zinc. Flux has so far seemed not to make a
difference either way- though I’d love to hear of one that prevented
the copper film!
Amanda, What kind of pickel are you using? I use Nickel Pickel on
brass and can’t remember having the type of problem that you
described. Perhaps that product could be helpful. Joyce Albers
Joyce, I’m just using Sparex for my pickle- I’ve only got room for
one pot, really. The nickel pickle sounds intriguing, though. Does it
remove the copper bloom, or don’t you get the bloom when soldering in
the first place? My stuff comes away from the soldering with the thin
copper coating. Sometimes. So I’ve been putting the responsibility on
either the metal compositions or my flux.
To get a shiny clean surface on brass, use the peroxide pickle first,
then Sparex.
The peroxide pickle is 3 parts hydrogen peroxide (the strength
available over the counter in stores), and 1 part white vinegar. Heat
the solution. It depletes quickly, within a few hours. It can be
"freshened" again with the addition of more vinegar. Don’t leave the
piece in the solution for too long, or it will be chemically etched.
Finish by transferring to the hot Sparex. If working in copper, you
can just substitute peroxide for the water in the Sparex, and when
you’re done for the day and the peroxide is
depleted, you have just Sparex solution left.
G’day; Brass is usually an alloy of copper and zinc; there is a
variety of brass alloys, gilding metal being one. Bronze is usually
an alloy of copper and tin, although there are other alloys which are
termed under the general name of bronze - for instance, beryllium
bronze (for electrically conducting springs, etc) and phosphor bronze
(copper jointing) and so on. But when all these alloys are strongly
heated some of the copper on the surface is oxidized to copper
oxide(s) One of these is black and the other is orange red. The flux
will often remove zinc as well as copper oxide, leaving a coppery
surface. If the work is placed in a pickle, this dissolves copper
oxide and also some of the zinc, thus leaving a coppery colour on the
surface. However, this will be so thin as to be only measurable with
very sophisticated equipment so it should be easily removed using
wet’n’dry papers or tripoli polish and a buff. In hard to get at
places, use tripoli on a rotary bristle brush, rotating at medium
speed.