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Bronze casting changing color


#1

Recently I have been casting bronze. I am using the Antique Bronze
from Rio I am puzzled about why I get a gorgeous golden color–on the
reddish to orange side, doing cuttlebone casting, and a brassy
looking yellowish color when doing lost wax casting process, using a
centrifuge.

Both batches came out of the same bag of bronze. The only difference
is that when doing the cuttlebone casting, I was making a small item
and melting a small amount of the bronze.

For the lost wax casting I had 4 items in the flask,each about the
same size as the one being cast using the cuttlebone technique, and I
had to have an extra allowance of metal for the sprues and the
button… Hence I used a larger quantity of brass, and the melting of
the metal using the lost wax technique took considerably longer. I
was using the same torch and gas for both.

Would the the difference of the quantity and the extra time needed
for the large batch to melt account for the change in the color of
the bronze?

Alma


#2

Hi Alma,

I use that stuff all the time. Really like it: it’s the only
commercially available bronze that I know of that really is bronze.
Just copper and tin. No zinc at all.

Never noticed any difference between cuttlefish and centrifuge
casting with it, but I’m melting with a hydrogen torch for both.
Perhaps it’s a surface layer? The environment in the cuttlefish mold
will be very reducing, so you’re going to get a very clean surface,
as such things go. The investment should be a bit more neutral, so
your torch will have a bit more influence in the surface character.
What’re you melting with?

Maybe take a sample done each way, and saw through them, to see what
the internal colors are?

Regards,
Brian.


#3
Recently I have been casting bronze. I am using the Antique Bronze
from Rio I am puzzled about why I get a gorgeous golden color--on
the reddish to orange side, doing cuttlebone casting, and a brassy
looking yellowish color when doing lost wax casting process, using
a centrifuge. 

My guess is that the burning cuttlefish is imparting a patina to the
bronze.

Try hitting one of your lost wax castings with a torch for a few
seconds, and see what color it turns. I’ve gotten some lovely colors
on cast bronze that way. Now if I could just figure out how to
preserve the color once I achieve it…

Kathy Johnson
Feathered Gems Jewelry
www.featheredgems.com


#4

I am a one man foundry owner/operator and cast with Everdure bronze
(copper and silica) almost exclusive but I have made (ancient
bronze) copper and tin and cast same for a customer. The tin in the
mix REALLY changed the color of this bronze right after casting as
well as how it would patina. The copper in these mixes is the main
metal reacting to make the coloration and what you are pouring into
can have a big influence on the “pour patina”. ANY surface or inner
"contamination" of the the “investment” a can/will cause a patina on
the casting. The colors one get from heating copper alloys are called
harlequin patinas and they are often VERY beautiful but they are most
often VERY fragile and transient, even if sealed. Often the “sealing
material” wax, lacquer or ?? will cause the colors to just disappear.
There are a few patina materials that will give coloration
approaching these transient harlequin type colors, but to me, they
NEVER are the same, those transparent, iridescent radiating type
colors.

Everdure alloy is available in from some companies but usually in 1"
cubes or ingots. It is also known as Marine or Navel bronze as it is
resistant to salt water corrosion. thus it is used on props, cleats
and the like. It is very easy to weld, especially with TIG but it can
be gas welded, but like silver, it is VERY heat absorptive so the
entire piece needs to be heated to near welding temp for the
materials to be joined.

You can check out some of my wife’s sculptures that I have cast at
our http://www.MLCE.net web site if interested. If you have any
further questions about these sort of materials, please feel free to
drop me/us a line. Also, Cynthia was a high end jeweler for most of
her life but when we met she was getting tired of working small and
wanted to sculpt, and I was willing and I guess able to learn about
bronze casting.

John Dach
MLCE.net


#5

John Dach, thanks for your comments about bronze changing color.

I checked out your wife Cynthia’s sculptures. They are absolutely
wonderful I particularly like the ones that merge the human and
animal forms showing the interconnectedness of all creation.

Alma


#6

Glad the info helped. Also thank you for taking the time to look at
Cynthia’s work. She started working in bronze with the Metamorphic
series, the woman/animal morfs. She has a couple of man/animal
pieces she is working on at times. When they will get done is
anyone’s guess as they are not of primary importance to her at this
time. Mixed media and the pastels are up front at this time…

John Dach