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Brass changing colors?


#1

What would make my brass turn colors in the ultrasonic? I am using
gesswin ultrasonic soap and heat and all my brass comes out red.
What’s up?

Thanks,
Tracey


#2

You are removing zinc from the surface… probably the solution is too
alkaline but might be too acid. Boiling silicon bronze in hot caustic
to remove tough ceramic shell investment turns the surface red goes
back to normal in time.

jesse


#3

Are there really no chemists or other science fanatics that could
help me solve this mystery and perhaps explain to me the finer
points of brass compositioni

Thanks,
Tracey


#4

Brass changing colors

Brass can have a wide variety of compositions, some found on the
internet include:

Leaded yellow brass contains approx. 67% Copper, 29% Zinc, 3% Lead,
and 1% Ti

Red Brass 85% Copper, 5% Lead, 5% Tin, and 5% Zinc.

Silicon Bronze approximately 95% Copper, 4% Silicon, and 1%
Manganese

alpha brasses have 37% of zinc

beta-brasses have 40-45% zinc

Admiralty brass contains 30% zinc and 1% tin

Aluminum brass contains aluminum.

The common thing here is the copper, nice red copper.

So which is yours

Lets assume it is a simple brass, in the range of 60% Cu 40% Zn. Zinc
is much more active than copper. Put the brass in a environment that
attacks metal, and the Zn goes first. This leaves a top coat of nice
pink / red copper.

See wikipedia on Selective leaching, where they state: Selective
leaching, also called dealloying, demetalification and parting, is a
corrosion type in some solid solution alloys, when in suitable
conditions a component of the alloys is preferentially leached from
the material. The less noble metal is removed from the alloy by
microscopic-scale galvanic corrosion mechanism. The most susceptible
alloys are the ones containing metals with high distance between
each other in the galvanic series, eg. copper and zinc in brass.

I think the answer is so simple that everyone thought someone else
would answer. I think we all have put brass in the pickle and
watched it turn red - same thing. But corrosion does not need a
overtly obvious acid to work, most electrolytic solutions will
promote some corrosion. Heat up the solution or agitate it (or both
in an ultrasonic) and the reaction is faster.

Marlin


#5
But corrosion does not need a overtly obvious acid to work, most
electrolytic solutions will promote some corrosion. Heat up the
solution or agitate it (or both in an ultrasonic) and the reaction
is faster

Do you consider an ultrasonic an electrolytic solutioni There is no
introduced current in our ultrasonic and these pieces are only in
there for around a minute. If this is increased by acidity would a
switch to a more ph neutral soap possibly stop the problemi.


#6
Do you consider an ultrasonic an electrolytic solutioni There is no
introduced current in our ultrasonic and these pieces are only in
there for around a minute. If this is increased by acidity would a
switch to a more ph neutral soap possibly stop the problemi. 

The only way not to have the potential for electrolytic corrosion in
a ultrasonic tank is to have the tank filled with ultra pure de-
ionized water only, no soap or anything else for that matter. Pure
water will not conduct electricity but even the slightest
contamination of the water will introduce ions that will conduct
electricity and then you have the possibility of electrolysis.
Anywhere there is more than one metal (stainless tank, wire mesh
basket strainer, your work, etc) in an aqueous solution there is
electrolytic action.

Soaps and detergents tend to be alkaline and push the pH up and we
often drag in pickle which tends to try to bring the pH down. In any
event you end up with an electrolytic reaction in the ultrasonic and
possibly some discoloration that accompanies it. You can alleviate a
lot of the problems by changing out your solution often (daily). Try
to use a plastic mesh strainer or basket in the ultrasonic so that
your work is not in contact directly with a second metal like a
stainless steel strainer. Using bottled distilled or de-ionized
water for your solution is not a bad idea as many water supplies have
lots of minerals in them that can aggravate the problem. If your work
has more than one metal in or on it do not leave it in the ultrasonic
too long as the ultrasonic action accelerates the rate of the
corrosion and under the right conditions can etch the work. If you
work in gold and platinum this is less of an issue then if you are
working in other metals.

I have gotten some truly strange colors on work from electrolytic
action in the ultrasonic, it almost always was from leaving the work
in dirty solution too long.

Jim

James Binnion
@James_Binnion
James Binnion Metal Arts


360-756-6550


#7

I checked my ultrasonic solution, and it was indeed ionic. I then
did a couple of tests with the brass I have around - not Jewelers
brass. I could not replicate your results - especially if you only
ultrasonic for a minute. It is possible that I did not get the
copper flash because I use a different solution, brass, and
ultrasonic - I only tried one of my the tanks. I also did not wait
for the solution to heat up.

If I were you I would try isolating the brass from contact with any
other metal - from the tank, wire hangers and baskets (try
suspending in a plastic basket). If it still does it, try cleaning
the tank and using plain water. If you still get the problem, I am
stumped - it must be the alloy or the casting residue.

Let us know what you find

Marlin