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Sand casting gems in place

I am keen to cast synthetic Sapphires and Rubys directly into silver buy sand casting them in place… I am well practiced in sand casting jewellery pieces, using my own black Zircon greensand (18% bentonite) and have tried a number of times but either the thermal shock or the contraction of the cooling metal causes cracking of the stones.
I have seen examples on the net of successful efforts and am wondering if there is anyone who may have any suggestions?

Sand casting will not give you the exact details that the wax can provide. There will be irregular amounts of metal around the stones. Plus the stones must be 100% perfectly ‘clean’ before being placed into this medium. I suggest a trial run and see what happens. I don’t suggest ‘sand-casting’ for small 1.50 - 2.0mm stones.

BTW, Don’t rapid cool the crucible by using water, let any hot crucible sit on the floor to SLOWLY cool down! Any stone, even diamonds will shatter if the crucible is subjected to cold water.

I’ve seen this happen and 3-4 days of setting stones in wax with 10 carats of diamonds and all went ‘bye-bye’. An honest mistake for the in-shop caster and he let out a mouthful of extremely “blue words”. All of us in the factory knew at that moment what happened…:>( The ‘wax-setter’ just turned white as a ghost!

Thanks,Gerry!… an “entertaining“ day in the workshop was had by all, it sounds.
I am particularly interested in the sand casting process for this project… there is plenty of information available for the gem setting in wax (lost wax) but none for direct casting in sand.
I’m aware that it is unconventional and has a certain amount of “in the lap of the Gods” randomness to be expected in the results.
I have been advised, via another source, that I might try heating my packed box ( cope and drag) before pouring the metal…Im keen to give this a try now , hoping that the sand holds its integrity and does not become loose and shift with the weight of the metal hitting it.
Thanks again for your insights and suggestions!

Just a thought on technical issues with sand casting: because the casting matrix (the sand) is generally ambient temperature versus 800f investment (recommended for gemstones which I can attest to) that in itself could cause alot of premature metal cooling and other issues.

Something to consider… the thread has been tantalizing to think about.

I tend to look at the design and then figure out the appropriate casting process; keeping the old horse in front of the cart. But if someone doesn’t have inhouse / instudio casting capabilities, I’d be diving in from a platform into the wading end of the pool.

Eileen

Since, to my limited knowledge, I believe that sand is not heat conductive and that when pouring a cast, the frame does not get hot, so it would be counterproductive to try to heat the frame, IMHO.

den

I do a lot of casting using delft clay. It works well for my purposes (small pieces with a flat side and irregular shaped ingots). Is there any reason why delft clay might work differently from the casting sand described by the original poster?..Rob

Robert - there are many different casting sand mixtures. Each one has different porosity. Craig Dabler has come up with a very fine casting sand that holds well but requires more venting than the more common mixtures. https://www.facebook.com/diycastings/ gives you more information and a source.
Judy H

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Bruce - Craig Dabler has a couple of utube vids of sand casting gems in place. Heating the box doesn’t make sense, what makes sense is very firm packing of the sand.
judy h

Thanks, Judy.

Great information!

Eileen

Judy…I took a look at Craig Dabler’s website and a few youtube videos on casting in place using delft clay. Thanks for the tip…Rob