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Weight formula for casting twigs in sterling silver


#1

Several of us in my metals class are experimenting in casting twigs
in sterling silver. Most of us have used the lost wax process before
but none of us, including the teacher, have cast organic items in
sterling. Is there a weight formula we can use? The twigs are dry.

Thank you in advance for any help provided. I love this site!


#2

Barbra,

My friends and I have used the lost wax style of casting to do twigs
as well. It seems the weight procedure doesn’t always come out right
since the density is different than that of the casting wax. So, I
looked in the “Complete Metalsmith” book by Tim McCreight.

It was explained how to determine how much metal is needed. Using a
beaker with gradients filled mid way with water. Submerge the twigs
or organics in the water in such a manner as to not add any
additional object that would affect the volume greatly. Mark the
water level. Remove the twigs then place your casting metal in the
beaker until the water level matches the level when the twigs were
in it.

Hopefully that will give you the proper volume of metal to replace
the twigs.

I hope I have explained that properly.

Or, weight the twigs and multiply that weight with a SWAG increase
in the multiplier. Normally I would use 2.5 times the weight of the
wax. With twigs I might would SWAG it to 3.0 to 3.5 times the twigs
weight. SWAG is a Scientific Wild A-- Guess, if you didn’t know.

Good luck,
ken
Ken Moore
www.kenworx.com


#3

Most of us have used the lost wax process before but none of us,
including the teacher, have cast organic items in sterling. Is there
a weight formula we can use? The twigs are dry.

I’ve cast about 150 twigs. I dry them thoroughly first, then spray
them with a clear acrylic spray to seal the branch. I usually cast
about 20 at a time in each flask. As far as weight goes, just make
your regular calculations treating the treed twigs as if they were
only wax. After casting, I run them for a bit in my vibratory
tumbler with steel shot. I have some pieces on my website in Gallery
1 if you’d like to look.

Donna in VA
http://www.sterling-ideas.com


#4

Hi Barbara:

I get a student with twigs every year or so. Unless it’s truly
massive, I treat it as wax, and add a little extra onto the button
for insurance. It’s worked so far.

If it’s large, measure the displacement, and figure your metal that
way. (This is in silver. If you’re talking gold, get serious, and
measure the displacement.)

Regards,
Brian Meek.


#5
Several of us in my metals class are experimenting in casting
twigs in sterling silver. Most of us have used the lost wax process
before but none of us, including the teacher, have cast organic
items in sterling. Is there a weight formula we can use? The twigs
are dry. 

General formula to determine multiplier is density of twig divided
by density of alloy.

Density of silver can be taken to be 10.5 or even 11 if margin of
safety is required.

Density of wood will depend on the wood.

Pine ranges from 0.35 to 0.5.

Fruit woods can be from 0.6 to 0.85.

It is unlikely that you run into any trouble if you assume 0.5 which
would give you multiplier of 22.

Leonid Surpin
www.studioarete.com


#6

Hello from Sunny SF,

I have casted for many years & we, too, have done a lot of organic
materials. This would include twigs, peanut shells, pistachio
shells, poppcorn, ferns, eucalyptus pods,& orchids…We always make
sure that these are sprued well, sealed with some kind of
sealant(paraffin wax, furniture polish, varethane etc.). It has
never occurred to me that weighing would be that much different than
calculating for waxes. Of course, we have always done more that a
few and we based the appropriate amount based on this:

Pre-weigh base and add all pieces/sprue up. Then weigh finished base
minus blank base (tare) to get weight of all pieces. Then multiply
by 10.46 to get casting weight in silver…BUT don’t forget to add
extra forthe button…So, for example on a 2.5" X 2.5" flask:

Filled base is: 2 dwts.
X 10.46 ( specific gravity for silver)= 20.92
Plus button–I would allow about 15-20 dwts extra…
Thus total could be 35.92/36 dwts to 40.92/41 dwts…
I’d probably cast at 41 dwts…This assumes a cone button for a
2.5 flank & fitted base.

So, I’m saying like the other metalsmiths/jewelers—Treat it like
wax, no real differences for calculating…Oh, by the way, when I
taught at CCA last year, we also did silk flowers-same way…A
student coated them with a sealant, built up wax thickness &
cast…And, we also did some insects, including dead bees & dragon
flies(no animals were killed to do these projects.

In other words, they were found expired) !!!

Ciao & good luck,
Jo-Ann Maggiora Donivan


#7

Thanks everyone for your expertise! We tried casting the twigs last
night (not too successfully I’m afraid). Everything seemed to go
wrong. We didn’t get a clean burn with most of the investments. We’d
sealed the twigs with left over spray paint the instructor had on
hand. Could that have been the problem? We didn’t try to cast those
investments. The 2 investments that did burn clean were semi
successful. They didn’t seal enough for the vacuum to work. Oh well,
it was an experiment and often you learn more by the mistakes than
the successes!


#8
We tried casting the twigs last night (not too successfully I'm
afraid). Everything seemed to go wrong. We didn't get a clean burn
with most of the investments. 

Remember when burning out things like twigs, insects, and the like,
you need to be sure the temps reach 1350. And it will generally take
longer at that temperature to burn out things like wood. There may be
some ash left in the mold, so just before casting, one can try
bumping the flask gently, upside down, to knock out obvious amounts
of ash. Some will remain. But you can reduce the amount sometimes.

We'd sealed the twigs with left over spray paint the instructor
had on hand. Could that have been the problem? 

Pigmented paint? Yes, that would be a problem. Many of the pigments
are metal oxides or similar salts. They don’t burn. So then you’ve
got a distinct residue in the mold. Use clear acrylic lacquer, or a
wax. Not just any old paint you’ve got.

We didn't try to cast those investments. 

Of course, if you didn’t try them, you don’t know how they’d cast.
Sometimes flasks with some discoloration etc. apparent can still cast
OK.

The 2 investments that did burn clean were semi successful. They
didn't seal enough for the vacuum to work. 

Well, that would have nothing to do with the twigs, burnout, or
investment. That would have to do with the condition of the flasks
and the silicone rubber pad. With vaccuum casting, you do have to now
and then make sure the bottom edge of the flask is even and not
damaged. You can restore worn flasks by sanding that bottom edge till
it’s uniformly bright. Then, in investing, also be sure not to
overfill the flask. You want the rim of the flask to seal on the
rubber. If the investment is overfilled, it won’t allow that.

Oh well, it was an experiment and often you learn more by the
mistakes than the successes! 

Often true. But the successes are kinda nice too… :slight_smile:

Peter