ceramic shell

Luiza · Post by **Luiza** » Thu Nov 06, 2003 5:50 pm

Hi
IÂ´ve just finished a plaster/silica mould, around a wax model. The wax model was very tricky, and IÂ´ve done 5 before I felt it was fine.
Now IÂ´ll go to the lost wax step, but IÂ´m afraid that the mould will crack during the casting. IÂ´ve donne all by the book, but IÂ´m still insecure.
Probabbly itÂ´s a very stupid idea, but what will happen if I put my mould inside a ceramic mould, and fill the spaces left with more plaster/silica? The mould has a cilindrical form and I have a cilindrical ceramic mold just 1in larger.
Is it absurd?
Thanks
Luiza

charlie holden · Post by **charlie holden** » Thu Nov 06, 2003 6:58 pm

No, it is not absurd. Another thing you can do is fill in between the plaster and the clay with sand. You could also just build a box out of small kiln shelves or bricks, put some sand in the bottom, put your mold in and level it, then fill in around the mold with sand.

Age old advice -- cast a simple shape of similar size first so you don't ruin lots of work.

Luiza · Post by **Luiza** » Thu Nov 06, 2003 10:12 pm

Thanks Charlie. IÂ´ll try the sand - seems easier

IÂ´ll remember your advice
Warm hug
Luiza

watershed · Post by **watershed** » Fri Nov 07, 2003 5:48 am

IF you are retro-fitting, you could use a piece of steel (pipe if the mold is small enough) as the outer, fill with sand, then the plaster. Most of the guys in my shop are using steel outers, instead of chicken wire etc, to contain the plaster. But steel is cheap here, and we have benders and welders. And most of the kilns are roll-outs, so not much heavy lifting.

Greg

Lauri Levanto · Post by **Lauri Levanto** » Fri Nov 07, 2003 8:19 am

Recently we have seen advices of constructing a box
around the mold. Ceramics, steel has been suggested, as well as Skamoil boards that you can joint with screws.

My kiln has unprotected elements, so I do not feel
confident with large steel saggars.

I have been thinking about ceramic (bisquit) boards
of different size that I can assembe with screws
to corner pieces.

Does that sound feasible?
What I need is a lot of one time saggars, so this kind of
modular construction is tempting.

-lauri

charlie · Post by **charlie** » Fri Nov 07, 2003 10:30 am

you won't be able to screw bisqued ceramic pieces. you'll have to make the molds as a single piece, unless you're going to prop them against each other and hold them there with something else (sand bed in a box, cut up kiln shelves, bricks, etc).

Nikki ONeill · Post by **Nikki ONeill** » Fri Nov 07, 2003 1:09 pm

Charlie:
Will any sand do? Do you know if common "Play sand" from the hardware store will work for supporting molds as well as be suitable for small-scale sand casting.? I was wondering about organic content, if any.
Thanks.
Nikki

Luiza · Post by **Luiza** » Fri Nov 07, 2003 5:51 pm

Nikki O'Neill wrote:Charlie:
Will any sand do? Do you know if common "Play sand" from the hardware store will work for supporting molds as well as be suitable for small-scale sand casting.? I was wondering about organic content, if any.
Thanks.
Nikki

Hi Nikki
IÂ´ve been using sand for re-firing pieces that are already slumped, to fire polish. I use ordinary sand , and just sift it and put in the kiln to dry. If it works in this case, beeing in touch with the glass, it certainly will work for our new use...
Luiza

Nikki ONeill · Post by **Nikki ONeill** » Fri Nov 07, 2003 6:28 pm

Thank you Luiza. I didn't know sand could be used in this way.
Have a great weekend.
Nikki

charlie holden · Post by **charlie holden** » Sun Nov 09, 2003 6:46 pm

Play sand is fine for supporting molds. Anything organic will be long gone by the time the glass gets soft. It may have some iron or other minerals in it though, which may discolor the glass if you get to slumping temperature and the glass is touching the sand. If you want to be safer when you're sand casting get "Cleaned Sand" for mixing mortar. It's not much more expensive at all. Available at building supply places.

Or you can get Olivine sand from a foundry supply -- which has much less silica content and so is safer for your lungs.

BTW, I think I'm going to follow the advice of the "Mixing It With the Best" cd and start using Olivine instead of silica in my casting molds. Anything I can do to get away from silica.

Lauri Levanto · Post by **Lauri Levanto** » Mon Nov 10, 2003 5:39 am

Hi Charlie,
sorry my floppy English.
I was not going to fasten with screws but with
nuts and bolts. Not tightening too much, and premade holes big enough to allow thermal expansion.

-lauri

rodney · Post by **rodney** » Mon Nov 10, 2003 10:25 am

Hi Charlie,
sorry my floppy English.
I was not going to fasten with screws but with
nuts and bolts. Not tightening too much, and premade holes big enough to allow thermal expansion.

-lauri
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what about wire, instead of the nuts and bolts

rodney

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ceramic shell

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Making a saggar

Nuts and bolts