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Molding sea shells


#1

I have a customer who wants to make silver and gold sea shells.

They have provided us with several beautiful tiny sea shells. Is it
possible to sprue them up, invest them, burn them out and cast? Or
what about just making a rubber mold of the items. Would the
vulcanizing heat be too much?

Thank you
j


#2

Hi John:

Teaching in a beach town, I’ve had loads of students come in with
shells of various types over the years. No luck in burning them out
(the calcium doesn’t burn), and they don’t tend to vulcanize well.
(They squish.) Best bet is a no-shrink RTV mold, and even then, you
may have to boost the thickness to get the mold to shoot.

Experiment. See what works best for you.

Regards,
Brian Meek.


#3
They have provided us with several beautiful tiny sea shells. Is
it possible to sprue them up, invest them, burn them out and cast? 

They are calcium carbonate. That doesn’t burn, so no, you cannot
directly cast them.

Or what about just making a rubber mold of the items. Would the
vulcanizing heat be too much? 

You can vulcanize them. I prefer though, using a liquid RTV rubber.
That way, you get no shrinkage. Some of those shells are already
quite thin, so preventing shrinkage might be an advantage. And the
silicone rubbers won’t stick at all to the somewhat porous shell, and
may give a slightly better mold. That was my experience with shells
at any rate. But either way works.

Peter


#4

do not try burn out many shells are poisonous and shells usually are
very strong it they are thick walled I would rubber mold them in
vucanizer if not then liquid silicon to mold directly from the shell

I guess question is what kind of shells are they

Teri


#5

Hello John, You can make vulcanized rubber molds directly from the
shells themselves. Put the mold in the vulcanizr and let the rubber
get warm before you clamp it down. This lessens the pressure on the
shell. I know you can do this because I have an entire collection of
them.

Have fun. Tom Arnold


#6

I had the same question about some soft coral, but I was told
there’s too much calcium there to burn out. You should make a mold of
them.

Janet Kofoed
http://users.rcn.com/kkofoed


#7

I’ve been intrigued with casting shells too but they won’t withstand
the heat of vulcanization and can withstand very little pressure as
far as I’ve found out. I’ll be following this thread so I’m looking
forward to what people suggest!


#8

I have used the material that dentist’s use for making impressions
for tooth crowns. Ask your dentist to get you the two part tubes, or
direct you for purchase…not cheap, but goes a long way.

Make a small box or unit to enclose the “putty”. Place the shell
pretty much down in the material, leaving an opening. Then, after
setting up, remove the shell carefully as not to rip the set up
"stuff", and fill the cavity with molten wax…let set up, carefully
"unfold" the material from the shell, sprue and cast. Very effective.

I have done tiny 1/2 inch or less cast in gold.

By the way, the shell will not burn out and leaves too much stuff in
the investment, and won’t give a casting.

This is fun, and addictive!!!
Rose Marie Christison


#9

I make a silicone rubber mold from the original, filling the aperture
with modellers clay to give it a bit of protection. Take a wax from
this and cast in silver, clean up the silver pattern and use it for
vulcanising. If you are careful with the first wax casting you will
not lose any detail on the end product. The silver pattern is a
damned sight easier to sprue than a seashell.

Nick


#10
I was told there's too much calcium there to burn out. 

This makes sense, but… I’ve had a student invest and burn out sea
horses that cast just fine, so go figure!

Noel


#11
This makes sense, but... I've had a student invest and burn out
sea horses that cast just fine, so go figure! 

A sea horse is a fish. A few bones, perhaps, but mostly proteins
such as in a tough skin. It’s not got a shell. I’d expect castings
from trying to burn out a shell to not work at all. I’d expect
burning out and casting a sea horse to perhaps give you a casting
with some porosity and perhaps a few other flaws, but most of it
should burn out and cast. Even bones have more protein, as well as a
spongy nature so there’s less mineral mass there to remain in the
mold cavity.

Peter


#12

Hi Noel,

I think seahorses have a lot less of that calcium “shell” material
than sea shells. Their “shell” is exoskeleton, more likely something
chitinous akin to fingernails rather than hard mineral shell. Maybe
like lobster or crab shell. I’m not totally sure about this and too
lazy after midnight even to google it but that’s my impression. And
my impression is that seahorse shells are relatively thin.

Marty Hykin in Victoria where we have a new Tonkinese kitten


#13

Noel

I was told there’s too much calcium there to burn out.

This makes sense, but... I've had a student invest and burn out
sea horses that cast just fine, so go figure! 

By “sea shells” most people mean the calcerous outer coverings of
molluscs. These won’t burn out because they are mostly calcium
carbonate, which is a fairly refractory substance. But "sea horses"
are a bony fish, with a much different composition. While the bones
in them will leave some ash, the total refractory content is much
lower, so burning them out will be more successful. It’s still a
better idea to mold them and cast waxes, if only because you only
need to use one specimen, instead of requiring one for each cast.
Despite sharing an environment with molluscs, the sea horse is much
more closely related to us than to any of them.

Andrew Werby
www.unitedartworks.com


#14

A seahorse is organic material while a shell is stone material, much
in the way your flesh is different from your bones.

Mike