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Casting bronze


#1

Hi Everyone, I don’t even know where to begin. I have never tried
casting Bronze before but I do know that Bronze can clump up and
oxidize causing it to not pour as well. Can anyone give me beginners
tips and advice from their trails and tribulations while casting
Bronze?

Warmly,
Rachel C. Dropp


#2

I recently gave a workshop in cuttlebone casting using ancient
bronze from Rio in order to keep the costs down. It cast beautifully.
The important thing is to keep the flame of the torch on it at all
times during the pouring. Hold the crucible as close to the sprue
opening as possible. Also pour quickly and smoothly. Each of the
casts came out perfectly. The downside was the cleaning and polishing
of the bronze… Lots of pickling, and then finally had to resort to
using an aggressive polishing with Bobbing compound.

Alma


#3

The clumping can be caused by a number of things.

Some alloys of bronze are more difficult to cast that others (I use
Everdure for casting sculpture). You may not be getting it hot
enough. Are you using any flux, this “can” make a big difference
with certain alloys (borax is a pretty good flux for bronzes). You
can also get clumping if you overheat the metal, thus burning out
some of the alloying metals and getting clumps. Dirty crucible?

Properly heated bronze (Everdure and this alloy is a bit more
difficult to cast than say Herculoy, which has a fare amount of zinc
in it to get it to cast better/easier, but I do not use it as it is
difficult to weld.) casts very well and gives great detail.

Hope this helps a bit!!!
John Dach


#4

Contact Todd Hawkinson. He’s quite the technician and taught casting
for many years. Todd, are you still here?

Margie


#5

I had brand new crucible, maybe I didn’t properly prepare the
crucible , usually I do a coating of boric acid on it before use it
for the first time (should I prepare the crucible differently). Also,
it did appear that the bronze was kind of crackeling while I was
heating it up so maybe I had the torch to high. My first attempt was
somewhat successful but still there was a bit of oxide at the bottom
of the crucible. My second attempt poured a little but then the rest
was clumped up, so I must of had the torch to high, I purchased
maganese bronze from Riom so maybe I also just need to use a
different type of bronze.

Would heating it up in another Kiln work rather then using a torch?


#6

Hi Rachel,

Yep bronze is a fairly easy metal to melt. When I pour my bronze, if
it’s under 1.5kg, I use a small mapp gas hand held torch on the
alloy as I’m pouring.

Regards Charles A.


#7

Hi Margie!

I have been casting quite a bit of bronze lately.

My experience is mostly with gold and silver but because of the
material costs I am looking for other metals that I can work
successfully. I have mixed results with the higher temperature
materials.

Currently I am casting:

White bronze
Yellow bronze
Brass
Chromium/nickel
Nickel copper
Copper
Sterling deox
White gold
Yellow gold

I am also trying (if at all possible) to mix my own brass and
bronze.

Torch melting is my first choice, Electromelt the second. I melt
with propane and oxygen. Regulating the torch flame is the most
important thing I could tell someone. All successful melting depends
on the right flame.

With any melting torch of any size you must determine how much
oxygen pressure to use. With a large torch I use 20 psi with a
smaller one it varies. This is also very hard to describe and not
demonstrate. This will be one of my future bench tube demos being
planned for this year.

In any event you must when finding the flame be able to open up the
oxygen on the torch until the knob is wide open. The flame is
regulated from the propane side. By cutting down on the propane, find
an oxidizing flame which is a reddish hissing flame. Add propane
until there is a bluish roar from the flame. You now have a neutral
flame every time you use the torch. Find this flame every time the
same way. Consistent flame use it critical to melting any metal.

I melt this way with every melt and have excellent results every
time.

One suggestion at a time, so this is where I would start.

Best regards,
Todd Hawkinson
www.southeastmn.edu/jewelry


#8

I have never used manganese bronze so I do not have any experience.
If possible call Riom and ask them what they think your problem is
all about. If you need to change bronze alloys, I would recommend
Everdure. Another alternative would be using the alloy that is used
to alloy gold, to reduce the carat of the gold, and just cast in the
alloy material. You can buy it in different colors for alloying for
white, yellow and red gold. Just some thoughts

John Dach


#9

Hi Todd,

Take care when you play with brass (especially with a melting
torch), the zinc fumes will make you very sick and eventually will
kill you, so a lot of ventilation and/or a fume mask.

Regards Charles A.


#10

Charles,

I have four Vent-A-Hood exhaust hoods with five exhaust motors in
the system. The zinc does smoke, but is well vented. For the fume
producing metals I try to furnace melt. Temperature is the deciding
factor there with the Electromelt temp maxing out at 2000 f.

The white bronze has been a pleasant surprise casting both with the
torch and furnace well.

Regards,
Todd Hawkinson
southeastmn.edu/jewelry


#11

Todd,

I do a lot of casting in gold bronze but I have not found a good
white bronze alloy that cas the “shine” like using silver. So far,
they are all dull that I have tested. Any suggestions?

Dana


#12

Hi Todd,

That is good to know, even a whiff of zinc fumes will make you
pretty sick, so taking the charge out of your furnace still required
caution.

I like to melt my bronze in a furnace, I have melted it in an open
crucible, but I like the furnaces better.

Regards Charles A.


#13

Dear Dana,

I am trying to mix my own white bronze with limited success.

The mix is 60% copper 20% tin and 20% zinc. I am trying different
mixing schedules because of the lower melting temperature of the zinc
and tin. I can cast it, but some of the material is quite brittle.
Looks great, but will mot allow any bending. It has a pewter look to
it and polishes up nicely. Not quite a silver look, but good enough
for some of my items.

The most success I have had is with casting the white bronze from
Rio Grande. The part number is 706-013. It is magnesium bronze, so it
can smoke a bit. Keep you vent on when melting anything! It has a
nice fluidity with the torch and will melt in the Electromelt at 1950
f quite well. Watch you flask temperature with either spin or vacuum
casting. Vacuum casting the same item that you spin can add as much
as 200 f to the flask temperature. Again a pewter look, but very
pretty. A plus on the material is that is clean from the cast easily.
The investment removal is a breeze.

If you need the formula ask for the MSDS Sheet which gives it
content. Cost is about $11.00 per pound. Not a bad price per penny
weight.

As for the dull look, I polish it just like silver and get a nice
shine. If you can cast pit free you’re in business.

Best regards,
Todd Hawkinson
www.southeastmn.edu/jewelry


#14

Hi Todd,

I’ve found that when you use 80% or less copper in a bronze alloy it
will get brittle, 80/20 (80% Cu, 20% Sn) will give you a bell metal
that is very white, and polishes nicely, however is a brittle at all
get-out.

90/10 will give you a lustrous bronze alloy, that polishes well, is
not brittle, and is tough enough to me made into functional swords
that can have a relatively durable sharpened edge.

If you want a white (white-ish) bronze that has a nice polish, you
will need to either add lead or nickel (which I wouldn’t do), or play
with the percentage of copper between 81-90%, maybe 85%.

Regards Charles A.


#15

Charles,

I’ve make the 90/10 yellow bronze without a problem. It cast well
and polishes great. I would love to make the white as nice as the Rio
stuff. But for the cost and effort I’ll keep buying the white.

Best regards,
Todd Hawkinson
www.southeastmn.edu/jewelry


#16
Watch you flask temperature with either spin or vacuum casting.
Vacuum casting the same item that you spin can add as much as 200 f
to the flask temperature. 

I’m new to casting and I’m trying to cast Rio’s white bronze with
mixed results. What would a good flask temperature be for vacuum
casting?

If you can cast pit free you're in business. 

Do you have any suggestions for me to cast “pit free?”

Thanks.
Whit


#17

Dear Whit,

In my casting class I note that there are approximately five groups
of items you can separate in casting temperature groups. This is for
both spin and vacuum casting.

Group 1 Filigree - 1150 to 1300 f

Group 2 Small rings & pendants - 1000 to 1150 f

Group 3 Light weight men’s rings & heavier women’s rings - 850 to
1000 f

Group 4 Solid men’s rings - 700 to 850 f

Group 5 Heavy weight (belt buckles) - 500 to 700 f

There is a bit of overlap some times, but you cannot jump from group
one to group three in the same flask.

One of the rules to follow is that the smaller pieces have to be
cast much hotter that the heavy ones and need there own flask and
temperature group.

I prefer to spin cast all white golds for quality purposes.

Best regards,
Todd Hawkinson
www.southeastmn.edu/jewelry


#18

Hi Todd,

I've make the 90/10 yellow bronze without a problem. It cast well
and polishes great. I would love to make the white as nice as the
Rio stuff. But for the cost and effort I'll keep buying the white. 

This an example of bell metal I mentioned earlier :-

http://www.ganoksin.com/gnkurl/1eg

The metal is quite white, even though the image doesn’t show this
feature too well (it’s an old photo).

Regards Charles A.


#19

Thank you for telling me the temperature appropriate the thickness of
the bronze pattern being cast. My question is this: how do I know the
temperature of liquid bronze in a crucible of a casting machine? What
happens if bronze is cast at the wrong temperature’

thank you.
Sally Parker


#20

If the temperature is too low the bronze wont melt properly, and
wont flow well, if it flows at all.

If the temperature is too high, you can burn off the lower elements
e.g. if you boil 90/10 bronze all you will be left with is copper.

Regards Charles A.