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Casting with silicon brass


#1

The material we have been using for casting both in our workshop and
at our production caster is a BRONZE alloy from Rio. We decided to
try another caster who uses silicon BRASS. The samples came back
with a very nice golden color; but after anneal and soldering them
they turned a very coppery color. Our hot pickle could not remove
what appears to be a copper coating. We tried using abrasives. 3M’s
yellow bristles (80 grit) barely worked. Zam was OK. Is it my
imagination or is BRONZE easier to cleanup than BRASS?

Harvey
http://www.kelferstudios.com


#2
3M's yellow bristles (80 grit) barely worked. Zam was OK. Is it my
imagination or is BRONZE easier to cleanup than BRASS? 

Well, it depends on the alloy of bronze and brass.

If it’s a tin bronze then it will be softer than a brass.

Regards Charles A.


#3

Try bright-dipping your silicon brass items after soldering and
pickling. The coppery look is probably cuprous oxide (Cu20)

Bright-dip can be either dilute nitric acid, or else add some
hydrogen peroxide to a new solution of the pickle (assuming you’re
using PhDown).

Judy Bjorkman


#4

Thanks, Judy

The pickle I use is a standard bisulphate pickle from Riogrande. I
will add hyrogen peroxide to this and see what happens. I suppose
the peroxide can be obtained from the local pharmacy. As far as
nitric acid, I don’t know where to purchase it.

Thanks again,
Harvey
http://www.kelferstudios.com


#5
The pickle I use is a standard bisulphate pickle from Riogrande. I
will add hyrogen peroxide to this and see what happens. I suppose
the peroxide can be obtained from the local pharmacy. 

The peroxide normally sold in pharmacies/drug stores is quite dilute,
being intended as a topical disinfectant/cleaning agent for wounds,
or as a gargle, etc. In short, very dilute. While this does have an
effect on pickle, it’s not all that much. You’ll do better if,
instead of a pharmacy, you look for a shop that sells beauty
supplies. In addition to the hair dyes and other stuff, these shops
also usually sell peroxide in about 15 to 20 percent concentrations,
for use as a bleaching agent on hair. That’s a LOT stronger than the
pharmacy stuff. That means you can add enough to make a difference
with your pickle, without at the same time overly diluting the
pickle… Do be careful with these grades of peroxide. While not yet
explosive or anything, these are strong enough to cause burns on
skin if you’re not careful. Use rubber gloves, and eye protection…
But more than that, and common sense, you don’t need extreme measures
to handle it. It’s used routinely in beauty salons, after all…


#6

Nitric is a tough one. I get it and pay dearly for it (special
hazard shipping fees) but I use it to make some of my own patinas and
it is well worth the cost of the shipping and the acid. Homemade
ferric nitrate is fantastic and I can change it via using different
"types" of steel. Great depth, color, etc

John Dach


#7

Thanks for responded to my question. Peter, before I received your
email I created a pickle using pharmacy grade peroxide and got very
good results. Next time I will use cosmetic grade. Do you use this
pickle routinely for brass and Silver?

arvey


#8
Nitric is a tough one. I get it and pay dearly for it (special
hazard shipping fees) but I use it to make some of my own patinas
and it is well worth the cost of the shipping and the acid. 

Yo might check with the chemistry dept/teacher at a local high
school or college. Most of them use various acids & may be able to
provide you with a place to get the acid you need. If you don’t need
much, they may be able to give/sell you what you need.

DAVE


#9

Hi Peter,

Thanks for the chemistry lesson. This explains why I wasn’t having
the copper coating problem when I solder BRONZE. Bronze has no zinc
to deplete like BRASS. Another solution to adding peroxide to the
pickle when pickling brass might be a product from RIO called RIO
KLEEN. It purports to pickle Nickle, Brass, Bronze and Copper. It
contains Sodium Bisulfate and Potassium Bi Chromate. I ordered some
and let you know how it turns out.

Harvey


#10
It contains Sodium Bisulfate and Potassium Bi Chromate. I ordered
some and let you know how it turns out. 

The potassium dichromate (aka Bi Chromate) is the ingredient that
allows for the pickling of nickel silver alloys. It is a hexavalent
chromium compound and as such it is a carcinogen. It has special
hazmat disposal requirements. It is also a skin sensitizer that can
cause severe contact dermatitis. You need to be careful with this
stuff. Do some reading about hexavalent chromium compounds before
you mix this stuff up and decide if you really want to use it.

James Binnion
James Binnion Metal Arts


#11

Peroxide and Pickle mix can be made to behave more agressively if
you heat the pharmacy grade hydrogen peroxide and pickle mix… I have
never used the 15 to 20 % hydrogen peroxide. Check your metal often as
it can be suprisingly active with higher temperatures.

ROBB


#12
Do some reading about hexavalent chromium compounds before you mix
this stuff up and decide if you really want to use it. 

If my memory serves (and it might not), in the movie Erin Brockovich
(with Julia Roberts, based on a real story), the chemical involved
that was such a problem for that community was hexavalent chromium
leaking into the ground waters… Now, movies sometimes change the
names to protect the guilty or innocent, etc, but I suspect in this
case, it’s probably the right name…

So if that’s the same, and the movie accuratly reflected the risks
of the stuff, I’d find myself being reluctant to get near it…

Peter Rowe


#13
Peroxide and Pickle mix can be made to behave more agressively if
you heat the pharmacy grade hydrogen peroxide and pickle mix.. I
have never used the 15 to 20 % hydrogen peroxide. 

I, on the other hand, have never used anything else, and I’ve never
had it fail to work. About 50-50 hot pickle and drugstore peroxide. I
stand over it and watch (or instruct students to do this) as it works
very fast, to remove the copper layer from brass after soldering and
pickling. Why go to the trouble to hunt down stronger stuff?

By the way, you theorists out there: If it is the pickling process
that depletes zinc and causes the copper surface, wouldn’t that
argue for trying Firescoff to solder brass so you don’t have to
pickle? Generally, this is the kind of thing I’d just go try, but I
never use brass in my own work, and I’m not going to take my
expensive Firescoff to class for my students to use!

Noel


#14

I have some pieces of brass and bronze that were soldered. I put
them in the RIO Kleen solution. Most of the red copper was removed
from the brass pieces. The bronze pieces looked less red.Then I
created a bisulfate/peroxide solution. and put the brass pieces into
the solution. The remaining copper was removed and the solution
turned blue. This tells me that I probably did not need the RIO
Kleen. product. Any roughness of the brass objects were removed in a
magnetic pin finisher. I still have some more experimenting with
bronze, but my gut feeling is that I can simply use a straight
bisulfate pickle, or perhaps one with peroxide added.

Harvey


#15

Hexavalent chromium?

Isn’t that the stuff the federal government finally admitted the
soldiers in the 1st Gulf War were exposed to… That caused ‘Gulf
War Syndrome’? And maybe the same stuff that was made so famous in
the movie Erin Brokovich?

I don’t think I would get in the same room with that stuff even if I
was in a bio-hazard suit!

Sb


#16
If my memory serves (and it might not), in the movie Erin
Brockovich the chemical involved that was such a problem for that
community was hexavalent chromium leaking into the ground waters... 

Yes the material in the movie and real life was a hexavalent
chromium compound (http://en.wikipedia.org/wiki/
Hinkley_groundwater_contamination). The term is shorthand for a
family of compounds (see
http://en.wikipedia.org/wiki/Hexavalent_chromium) where the chromium
is in the +6 oxidation state since the name hexavalent they are all
carcinogenic.

James Binnion
James Binnion Metal Arts


#17
By the way, you theorists out theRe: If it is the pickling process
that depletes zinc and causes the copper surface, wouldn't that
argue for trying Firescoff to solder brass so you don't have to
pickle? Generally, this is the kind of thing I'd just go try, but
I 

My thought is that the “copper surface” is not copper but is red
cuprous oxide (Cu2O). With brass, the red surface is neither caused
nor removed by pickling but must be removed by bright-dipping.
However, that doesn’t vitiate your interesting suggestion to try
Firescoff (if someone else out there wants to try it --I don’t have
any Firescoff).

Judy Bjorkman