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I would like to create a plaster mold, I have a book that explains reciepes, but do I really need silca and other stuff do make a mold?
Can't I just use the standard Plaster of Paris? Need answer asap. Thanks to all that respond.

would like to create a plaster mold, I have a book that explains reciepes, but do I really need silca and other stuff do make a mold?
Can't I just use the standard Plaster of Paris? Need answer asap. Thanks to all that respond.

Yes. No. Okay. No problem. Brock

Interesting that you should buy a book that tells you how to do something you don't know how to do and then challange it!

Plaster of paris won't stand up to the heat of the kiln.

Silica is used to make the plaster stand up to the heat of the kiln.

Pay attention to the book; sounds like who ever wrote it knew what they were talking about.

Jerry

Jerry,

I suggest you read the long (3 page) and informative thread on the second page of this board:

http://www.warmglass.com/phpBB/viewtopic.php?t=640

It isn't trivial (in my experience) to make cast molds that stand up to the stresses of glass firing. Thanks to the advice of the learned people here, my latest attempt (45% hydrocal, 45% silica, 10% grog and a very thoroughly dried mold) survived 1500F with just one hairline crack that didn't affect the glass.

Simon

Simon,
You missed my point. The original post seemed to me to be from someone who didn't want to go through the work of learning proper mold making; he did ask if silica was necessary as I recal rather than just plaster of paris.

My intent was to encourage him to do the kind of research you've obviously done to learn methods of mold making which will work. If from that you got that I was trashing your kind of formulas, I sincerely appologize, because I was NOT.

Starting with a simple mix of plaster and silica is a good beginning, but there are lots of other formulas out there, including yours, which produce great results. My goal was to get him into those formulas so he could enter the wonderful world of casting with tools that would serve him well.

And, just for the record, my formula of silica, plaster and TALC has yet to produce a crack in the last dozen or so firings. Doesn't mean I've got the best formula in the world, but I do have one I've worked hard to perfect, and took the guidance of other casters here to work out.

Thank you for your post and I hope to hear from you again.

Jerry

I tried making molds out of various plasters we had around the house and they turned to dust when I fired them. But it was good practice, and would be a good way to make a practice mold or a reverse mold that you would make your permanent mold from.
Does anybody have some good sites to go for these ingredients? I haven't found anything so far that wasn't wholesale only.

[quote="Jerry"]Simon,
You missed my point. The original post seemed to me to be from someone who didn't want to go through the work of learning proper mold making; he did ask if silica was necessary as I recal rather than just plaster of paris.
Jerry, don't assume he didn't want to go thru the work, maybe he just didn't know what the silica was for, or he can't get it! I find that's the problem with formulas for a lot of things. They tell you what but not why, and not where do you get it.
I would like the name of the book. It sounds interesting.

Strega wrote:I tried making molds out of various plasters we had around the house and they turned to dust when I fired them. But it was good practice, and would be a good way to make a practice mold or a reverse mold that you would make your permanent mold from.
Does anybody have some good sites to go for these ingredients? I haven't found anything so far that wasn't wholesale only.

What ingredients do you mean? Plaster and silica?

If so, ANY pottery place will have them. Since you buy them by the 50 pound bag, it's usually more economical to buy locally than to have them shipped. For molds, ask for Pottery Plaster #1 and 200 mesh silica -- both are widely available at ceramics places. $20 should buy you a 50 pound bag of each -- retail.

Jerry,

My apologies. I misaddressed my post. It was directed at the originator of the thread, not at yourself. If you re-read it in that light (minus the first word "Jerry" perhaps it will make more sense.

Simon

Jerry wrote:Simon,
You missed my point. The original post seemed to me to be from someone who didn't want to go through the work of learning proper mold making; he did ask if silica was necessary as I recal rather than just plaster of paris.

My intent was to encourage him to do the kind of research you've obviously done to learn methods of mold making which will work. If from that you got that I was trashing your kind of formulas, I sincerely appologize, because I was NOT.



Jerry