Casting old sprus and quench time

Jewelry Discussion
1

Dear All,

I do cast quite a bit. At least twice a week when busy. I have
recently started to cast white and yellow bronze. I hope to mix my
own metal this week. My castings have been excellent except on one or
two flasks.

I have questions on two things. The first is any quench time? Do I
even bother to quench? With casting gold, silver, and platinum I
always have. I don’t believe a foundry can quench a bronze casting.
Should I?

The second is a remelting old sprus. Again is the spru button
remelted with new added? Many times with gold and silver I’ll remelt
several times without adding new. I have so far been mixing about
50/50 new and old.

The cast that did not turn out was very brittle and the pieces broke
when bent.

Melt temperature for both is 1900f.

With the bronze I’m mixing myself I should be able to save a bit of
money, but it’s not too expensive anyway. I’ll let everyone know the
result of mixing your own. You can buy a pound of bronze for about
$12.00. That’s about .05 cents a pennyweight. The white bronze has a
good looking color.

I also have started to cast Nickel Chromium which is the material
for all the white metal class rings. This is a lot harder to do than
our traditional silver and gold casting. A lot cheaper than you can
believe, but very much like casting Platinum. The main problem I see
here is the investment removal from the casting is traditionally done
with hydrofluoric acid which is quite nasty stuff. I have some of the
Densply NeyClean SP investment remover, but it does not work well on
the higher temperature investment. Any ideas?

Hopefully some answers will come from someone who is actually doing
this. My research has lots of answers. I’d like to talk to someone
who is actually doing some of this.

Best regards & thanks,
Todd Hawkinson
Southeast Technical College
southeastmn/jewelry

2 
I have questions on two things. The first is any quench time? Do I
even bother to quench? With casting gold, silver, and platinum I
always have. I don't believe a foundry can quench a bronze
casting. Should I?

Bronze is a funny animal, if you quench it after casting, it will be
in an annealed state, if you let it air coll it will still be in an
annealed state. This may be a quirk of the 90/10 bronze I alloy
myself, Bovin says something similar.

The second is a remelting old sprus. Again is the spru button
remelted with new added? Many times with gold and silver I'll
remelt several times without adding new. I have so far been mixing
about 50/50 new and old.

Well you can, but it’s not as nice as a “fresh batch of cookie
dough” :wink:

The cast that did not turn out was very brittle and the pieces
broke when bent. 

Melt temperature for both is 1900f.

Could you outline your melting procedure for me please e.g melting
in an open crucible… etc. etc.

My procedure for alloying 90/10 bronze to make a bronze ingot or a
casting. *Note: I use the same procedure whether I use a large
furnace or a micro furnace, I use open crucible only at school. I use
propane, as the fuel, and I like to use Delft clay.

  1. Fill the empty crucible with flux, then empty it out.

  2. Put in my measured quantity of tin

  3. Cover with granulated copper

  4. Put in come more flux

  5. Turn on the furnace

  6. Check periodically for the bronze to melt

  7. When melted stir with a green stick to remove impurities

  8. a) For a small melt: When pouring into the mould keep a torch on
    the liquid metal, until it has all entered the mould, and if there
    is any surplus, into your ready surplus mould.

b) For a larger melt: A torch isn’t necessary as the heat from the
volume of the molten bronze alleviates the need for the use of a hand
torch.

For remelting bronze, the procedure is pretty much the same, but
it’s very important to make sure you don’t overheat your bronze, or
boil it, otherwise you will burn off tin as vapour.

With the bronze I'm mixing myself I should be able to save a bit
of money, but it's not too expensive anyway. I'll let everyone know
the result of mixing your own. You can buy a pound of bronze for
about $12.00. That's about.05 cents a pennyweight. The white bronze
has a good looking color.

Personally I don’t like zinc for health reasons, and when I use
solder I now wear a fume mask, as I appear to be sensitive to zinc
fumes.

But let me know how you go.
Regards Charles A.

3

Hello, I think when you cast bronze,the sooner you quenchthe flask,
the softer and the more flexible the metal will be.

Have fun.
Tom Arnold

4 
Bronze is a funny animal, if you quench it after casting, it will
be in an annealed state, if you let it air coll it will still be in
an annealed state. This may be a quirk of the 90/10 bronze I alloy
myself, Bovin says something similar.

That will be true of any alloy which cannot be age hardened. The
reason some alloys are annealed when quenched and hard when air
cooled is that they cool slowly enough to allow some age hardening to
take place. Alloys which don’t have that capability will not be much
different whether quenched or not, though with slow cooling there may
be some small difference in grain size…

Peter Rowe

5

Whether you can melt old sprues, vents and trimmings from cast
bronze and depend on it working depends on several things. The most
important is the nature of the alloy you are using… Is what you are
casting really bronze?

Most people do not distinguish between bronze and brass. If it is
bronze, what kind of bronze? The color of the metal, though a clue,
is not adequate to determine the alloy. Further, there are some
alloys that can not be melted multiple times without changing the
nature of the material. One of the most notable is aluminum bronze.
When melting it a second time, you end up with a mix that does not
flow well. I have not checked it out but I think that the earlier
melts vaporize or oxidize the aluminum so that it is lost from the
mix in fumes or in the dross. Further, when you melt mixes of
different alloys you find that they are not always compatible. If
you are sure to reuse sprues in melts of the same alloy, you are
generally safe.

There is plenty of on the internet and in the library
that will help you decide whether a particular a particular alloy can
be cast multiple times (Si-bronze sprues and rejects can be added
back to the crucible without worry. Si-bronze pours smoothly and is
yellow in color.)

Vaughan

6

Hi Todd; I think 50/50 is fine on just about any metal 1900 is too
hot for silver 1790 isabout as high as I go on small stuff. I let a
4"x9" flask cool for about 20 min before quenching if you are
casting a master or want something to be really nice use all new
metal.

You really haven’t mentioned one of the things I think is the most
important which is the flask temp a good starting point would be
about 900 for the final soak before casting. you can go up or down
from there depending on the results.

You can always cast one flask cool it and quench it then look at it,
leave the others in the oven, and turn the temp down and try
another, remember to let the flask soak at the new temp for
2hours/100 degrees up or down.

That should give you some things to think about,

good luck my friend,
Gregg

7 
There is plenty of on the internet and in the library
that will help you decide whether a particular a particular alloy
can be cast multiple times (Si-bronze sprues and rejects can be
added back to the crucible without worry. Si-bronze pours smoothly
and is yellow in color.)

Well the definition of bronze changed in the 1920s-30s, up until
that time bronze had to have a tin component, with the advent of
silicon bronze (aka silicon brass), it changed.

Silicon bronze (silicon brass), contains neither tin, nor zinc, yet
it gets the monica.

White bronze, does contain tin, but it also contains zinc.

I like my bronze to be uncomplicated, and “bronze” coloured. 90/10
has been used for centuries, and it’s a nice mix to work with.

Regards Charles A.

8 
That will be true of any alloy which cannot be age hardened. The
reason some alloys are annealed when quenched and hard when air
cooled is that they cool slowly enough to allow some age hardening
to take place. Alloys which don't have that capability will not be
much different whether quenched or not, though with slow cooling
there may be some small difference in grain size...

The only real way to harden 90/10 is work hardening. The edges of
bronze swords were done this way, after being casting in limestone
moulds.

Regards Charles A.

9

I cast sculptural bronzes and in this area, the 2 main alloys that
are common are Herculoy (copper, silica and zinc) and Everdur (copper
and silicon). I use Everdur. Herculoy is more fluid and pours a bit
better than Everdur, due to the zinc content, but the zinc burns out
during each melt and the color changes. Also if any welding is
needed, there is more trouble getting filler material/parent material
color match, again the zinc fumes/burns out. Everdur, having no low
temp materials in the alloy, does not have this problem of color
match so remelting previously cast metal does not present color
problems as Herculoy does. Also Everdur is MUCH easier to weld and
welds are cleaner, again because of the lack of zinc in the alloy
mix.

My wife uses the alloying used for reducing the karat or carat (which
ever spelling you choose to use) of casting gold if she wants a less
expensive, copper/gold colored metal for designs, displays and the
like. There are many other bronze alloys, one of them being aluminum
bronze as stated previously (below). There are machining bronzes,
self “lubricating” bronzes and bronzes made to be worked hot and
others to be worked cold.

Lots of choices so some research may be in order to get the correct
alloy for what ever you are trying to do.

Good luck!!
John Dach

10 
I like my bronze to be uncomplicated, and "bronze" coloured. 90/10
has been used for centuries, and it's a nice mix to work with.

So is silicon bronze. I work with it all the time. I have investment
cast it-- which is not a challenge at all–but mostly I fabricate
with it. Forging, rolling, forming, hot bending and welding. I often
reuse scrap by melting, pouring and rolling out stock.

I have just completed a sculptural piece which hangs from the
ceiling on a 5’ bronze chain made of oval links that begin with 3
1/2" long links forged from 6mm stock and taper down to 3/4" long
links forged from 4mm stock. The links are torch welded.

I have made a lot of brooches and neckpieces with it over the years.
I love its color, weight and historic associations.

On Line Metals in Seattle and Atlas in Denver have it in stock. Rod
and sheet (plate).

Take care, Andy

11

Hi Andy,

It’s just a personal preference, phosphor bronze, silicon bronze,
and there are a few others they’re a tad more pink or gold than I
like.

I use 90/10 for its historical significance, 90/10 been in used for
more than 2000 years. For me silicon bronze is a new kid on the
block, having only been formulated in the early 20th century.

For a sculptor I can see the attraction, in that silicon bronze is
available in brazing rods, so defects, and sections can be filled,
and joined without a noticeable colour variation in the repair or
join. It’s also very convenient, because it’s an industrial metal,
and there’s quantity available, for a relatively modest price.

Although 90/10 costs more. I like to alloy my own, it makes me feel
more a part of the process. I was toying with the idea of getting
some malachite, crushing and refining it, doing the same with some
tin ore… however malachite is pretty, and I can’t bring myself to
destroying the stones :frowning:

Regards Charles A.

P.S. If I want large sheets of 90/10 I have to make them… and
that’s a hell I don’t want to go into just yet.

12

Hi Charles,

Not saying one is better than the other. I used to use commercial
bronze and naval bronze but I settled on Everdur (silicon bronze) and
like it. If something else catches my eye, I’ll give it a go too.

I usually weld it by rolling out a strip of the same material into a
thin wire. So the weld is the same metal thru and thru.

Take care,
Andy

13 
Not saying one is better than the other. I used to use commercial
bronze and naval bronze but I settled on Everdur (silicon bronze)
and like it. If something else catches my eye, I'll give it a go
too.

Naval Bronze and Commercial Bronze are really both brass alloys in
that they are copper zinc alloys Commercial Bronze is 90 Cu 10 Zn and
Naval Bronze is 59 Cu, 40 Zn, 1 Sn. One percent tin but still
primarily a copper zinc alloy aka brass.

James Binnion
James Binnion Metal Arts

14

Hi Andy,

Not saying one is better than the other. I used to use commercial
bronze and naval bronze but I settled on Everdur (silicon bronze)
and like it. If something else catches my eye, I'll give it a go
too.

It’s all personal preference, hence it’s what “you” like, or your
customer wants, that matters. Some of my customers are
dyed-in-the-wool re-enactors, and demand the right formulae. 90/10 is
a common request, but there are other formulae that have been
requested, even a bronze with 1% iron in it (which I haven’t been
able to alloy yet)…

That’s interesting that you use the same material for welding, do
you use a MIG or TIG, I’ve heard that these devices will allow you to
use whatever metal to weld with.

With torch welding, I’d probably have to add a bit more tin for my
90/10, but that would screw the colour, it doesn’t take much tin to
change the colour of the bronze.

Regards Charles A.

15 
That's interesting that you use the same material for welding, do
you use a MIG or TIG, I've heard that these devices will allow you
to use whatever metal to weld with

Relative to welding Si-bronze, I use several methods. For small areas
I use an Oxy-acetylene torch with scrap sprues and vents (of the same
metal) for filler. When no scrap is available I use Si-bronze brazing
rods from a local welding supply house. Otherwise I use MIG with
Si-bronze wire. Mig is easier, faster and heating is more local (less
worry about a desired detail melting and falling off). The above is
relative to sculptural welding ranging in size from a few ounces to
many pounds. For small stuff (jewelry) I use a Smith torch for heat
and mig wire for filler. In all this it is important to use a good
brazing flux. I heat the end of the filler wire and dip it into the
flux powder, a bolus of which will adhere to the wire. I find this to
be far easier than soldering sterling silver.