Sand Mold Basics - WarmGlass.com

Sand Mold Basics

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Barbara Cashman
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Sand Mold Basics

Postby Barbara Cashman » Wed Jan 16, 2013 10:26 am

I am needing a basic, step-by-step tutorial on making a 12x12 open-faced sand mold using "play" sand. Need to impress a pattern to come out crisp and sand-free. I also have some olivine sand, but more "play" sand. Help, please. Thank you, in advance.
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Re: Sand Mold Basics

Postby pshash » Wed Jan 16, 2013 11:58 am

Richard La Londe has it in his first book I think.

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Re: Sand Mold Basics

Postby Barbara Cashman » Wed Jan 16, 2013 12:10 pm

I have the book. Forgot it was in there. He is using olivine. would there be any difference in using playsand?
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Re: Sand Mold Basics

Postby Bert Weiss » Wed Jan 16, 2013 1:12 pm

Barbara Cashman wrote:I have the book. Forgot it was in there. He is using olivine. would there be any difference in using playsand?
I once found out the difference, the hard way. Play sand has a higher COE than glass. Olivine sand has a lower COE than glass. I tried using my sand mix between layers of glass, and the olivine resulted in cracked glass. The play sand did not. This only has bad effect when the sand is sandwiched.

For my work, I use a 10mm thick sandbed, 25% alumina hydrate 75% sand, by weight. I have tried all sorts of sand with pretty good success, including some sandblast grits. Dry plaster works instead of alumina, but the mix is not as durable. Eventually the plaster leaves white schmutz on the glass. WIth plaster, you can get away with 80/20.
Bert

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Barbara Cashman
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Re: Sand Mold Basics

Postby Barbara Cashman » Wed Jan 16, 2013 8:42 pm

I have just been told by the foundries that olivine is no longer available.The foundry is using a product called Green Diamond, which they say is just crushed glass. So. what are the glass casters using instead?
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Re: Sand Mold Basics

Postby Bert Weiss » Wed Jan 16, 2013 9:07 pm

Barbara Cashman wrote:I have just been told by the foundries that olivine is no longer available.The foundry is using a product called Green Diamond, which they say is just crushed glass. So. what are the glass casters using instead?

Last I knew, olivine was quarried somewhere near asheville NC. I haven't bought any for several years now. Olivine is magnesium sand, as opposed to silica sand. I recall Greg Rawls telling me that silica dust is a problem, but sand is not dust.
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Re: Sand Mold Basics

Postby Barbara Cashman » Wed Jan 16, 2013 9:47 pm

Bert, I appreciate your response. But please read the post again. there is no olivine.
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Re: Sand Mold Basics

Postby Bert Weiss » Thu Jan 17, 2013 1:50 am

Barbara Cashman wrote:Bert, I appreciate your response. But please read the post again. there is no olivine.
This article says that green diamond is silica free, so it can't be ground glass.
http://www.afsinc.org/about/content.cfm?ItemNumber=12750

Just get any kind of sand and try a test. The particle sizes are key to the look you get. You want a matrix of different particle sizes. The larger you get, the more texture to your casting.

I've done tests with dozens of materials that are stable at 1500ºF. Each yields a different look. Some stick, some don't.
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Re: Sand Mold Basics

Postby Barbara Cashman » Thu Jan 17, 2013 9:12 am

Thanks. I hadn't looked up Green Diamond. After I was told it was 3x the cost of olivine, I didn't pursue it. I'll get a bit from the foundry and test.
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Re: Sand Mold Basics

Postby pshash » Thu Jan 17, 2013 10:13 am

I would email Richard and see what he is using for his workshops. I know he is still fusing in sand.

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Re: Sand Mold Basics

Postby rosanna gusler » Thu Jan 17, 2013 2:01 pm

try www.unimin.com rosanna
artist, owner of wanchese art studio, marine finisher

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Re: Sand Mold Basics

Postby GuyKass » Thu Jan 17, 2013 3:10 pm

For what it is worth. I have used regular foundry sand mixed with about 4-5% Bentonite and it worked fine.

It held fairly good detail, and the sand didn't stick to the glass (frit.)

Most glassblowers who do any kiln casting use a dirty Acetylene soot as a release agent.

We've also used a solution of very watered down molasses - In fact if memory serves me right, that is the agent I used for the castings referenced above.

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Re: Sand Mold Basics

Postby Morganica » Thu Jan 17, 2013 3:40 pm

You can still obtain olivine, it's just not being mined in the US (or possibly all of North America, not sure) anymore and so it's more expensive. The Scandinavian variety is supposed to be very good, and I think it's still being mined in India and China.

Just for accuracy--olivine, Green Diamond and playsand ALL contain silica (SiO2). What they're talking about with "no silica" is the form the silica takes--crystalline or amorphous. Crystalline, or "free silica" is the one to worry about, silicosis-wise, and there's little or none in olivine, Green Diamond or Biasill (another alternative to olivine). Playsand typically is rich in crystalline silica, so it's more of a challenge to work with.

I've talked with an aluminum casting guy that really likes Biasill--says it produces finer detail than the old olivine, makes a more durable mold and gives a better surface that needs almost no cleanup--but it's supposedly bloody expensive. He mixes a 50-pound bag with a pound or so of powdered fireclay and mists it with water, says it lasts through several hundred castings. Be interesting to try it with a kiln casting.
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Re: Sand Mold Basics

Postby Kevin Midgley » Thu Jan 17, 2013 5:33 pm

Cynthia if you are going to try that you need a thorough mixing which, without one of these http://www.leevalley.com/en/garden/page.aspx?p=10338&cat=2,2180,33222 might be a little difficult to ensure.
I never did try reducing the density of the LaFarge fondue cement I once had.....

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Re: Sand Mold Basics

Postby Bert Weiss » Thu Jan 17, 2013 7:57 pm

GuyKass wrote:For what it is worth. I have used regular foundry sand mixed with about 4-5% Bentonite and it worked fine.

It held fairly good detail, and the sand didn't stick to the glass (frit.)

Most glassblowers who do any kiln casting use a dirty Acetylene soot as a release agent.

We've also used a solution of very watered down molasses - In fact if memory serves me right, that is the agent I used for the castings referenced above.
Guy, I took a hotcasting in sand workshop at Pilchuck. Yes, we used soot from an acetylene torch as the separator. Some work was done without it, so the sand would intentionally stick. These molds are made with sand, bentonite, and water.

For kilncasting we need a different protocol. Carbon will burn up and disappear by the time the glass slumps in a kiln. So we use a refractory separator. The 2, I know of, are plaster and alumina hydrate. In the kiln we work dry. There is no reason to include bentonite that I know of. In my practice, I found plaster to eventually leave white scum, so I switched to alumina. The alumina is pretty durable.
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Re: Sand Mold Basics

Postby GuyKass » Thu Jan 17, 2013 8:37 pm

HI Bert-

That is very interesting about the soot burning away. I've never actually tried it but many of my friends have. We always used the molasses deal.

I always assumed the Bentonite was to hold the grains of sand together and in turn get better definition if you are just pushing and pulling something into the sand.

I will have to run some tests both ways one of these days.

Thanks for the info.

Guy

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Re: Sand Mold Basics

Postby Bert Weiss » Thu Jan 17, 2013 8:48 pm

GuyKass wrote:HI Bert-

That is very interesting about the soot burning away. I've never actually tried it but many of my friends have. We always used the molasses deal.

I always assumed the Bentonite was to hold the grains of sand together and in turn get better definition if you are just pushing and pulling something into the sand.

I will have to run some tests both ways one of these days.

Thanks for the info.

Guy
When you hotcast, there are 2 things going on. The water is in the mix to make the clay in to a binder. It also creates steam. Between the carbon and the steam, the sand does not stick. The molten glass spends only enough time in the mold to chill to the point where it will maintain it's shape.

Today is the birthday of one of my teachers, Bertil Vallien. He was a pretty interesting guy to get to know. For any Mainers out there, he has a copy of some Bert and I record albums. Ayup.
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Re: Sand Mold Basics

Postby Morganica » Thu Jan 17, 2013 9:54 pm

Kevin Midgley wrote:Cynthia if you are going to try that you need a thorough mixing which, without one of these http://www.leevalley.com/en/garden/page.aspx?p=10338&cat=2,2180,33222 might be a little difficult to ensure.
I never did try reducing the density of the LaFarge fondue cement I once had.....

Actually, I've done the bentonite+sand thing, but not quite that fancy. I just shoved it in a barrel and rolled it all over the yard. ;-)
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Re: Sand Mold Basics

Postby twin vision glass » Sat Jan 19, 2013 11:11 pm

Quick Question. Are you kiln casting or Hot casting. I have had wonderful fun with both :
http://www.twinvision.fusedglassartists ... sting.html
http://www.twinvision.fusedglassartists ... ndles1.jpg This piece was done in the kiln in sand mixture of :
-Just for the sake of it think of 100 pounds of Silica Sand (or better yet, olivine if you can find it) Play sand is dirtier but you can burn it out if you must BUT best to use 2 grids so sand settles well. . (80 girt and 120 grit ) the finer the sand the less it breaths and can cause bubbles if toooo tight.
Then add 5 % percent Bentonite and 10 % percent #1 Pottery Plaster. Mix to the point that you can press your hand into the mold mix and come out with a perfect hand , or pick some up squeeze, and throw ball up in air, if it stays together you are ready to go. If NOT add more plaster and abit more bentonite. ********* No water for Kiln casting
-Then when you have your images pushed into sand (use white TALC powder from the Potter Supply store ) and dip your image into it. Tap into sand , then do again and tap into sand , and so on until design is figured out and you are happy . Push small finished glass pieces in toooo if you want to BUT have them ground as anything pushed into sand will not soften the edges so if it is sharp, it will be sharp. AFTER you have desired look, sprinkle TALC onto sand or rather sift so NO sand can be found but make sure you do not cover the ends of glass impressions or it will not melt to larger cast piece. So there we go. Any other questions please ask. I used to do alot of kiln sand casting. If my mix is right and set up is right, THEN you can lay up to 100 pounds of glass onto this mix. BUT I usually design with Fiber pieces at each corner that will stick up higher than my image design so I do not flatten my design when I start to load glass. That is how the piece above was made. I also have mold mix 6 molds in the design as well , but that is another story. It gives such fine lovely detail BUT the release from the glass is primer on mold mix 6 and dried out before loading as apposed the the TALC on the sand. You do not want Talc on Mold Mix 6 or you get tiny tiny bubbles. Also SILVER irridescent also can cause some bubble issues with talc and mold mix 6 . Irri glass also is a GREAT release with the Talc.
Leslie
http://www.twinvision.fusedglassartists ... sting.html here we are casting into Olivine sand and bentonite and water with Acetaline Torch to carbon sand
http://i228.photobucket.com/albums/ee40 ... /Scan1.jpg (hot cast into Olivine Sand at Pilchuck)
http://i228.photobucket.com/albums/ee40 ... G_9073.jpg This is hot casting into DRY mix at Pilchuck because I am also hot casting into the mold mix 6 mold with Uroboros glass Powders . Our release for Hot Casting into Mold Mix 6 was different than kiln casting with it as the spray Graphite was not good for kilns but Boron Nitride did work with hot casting for a release on the Mold Mix 6. So many years experimenting and so many projects learned the hard way.
http://i228.photobucket.com/albums/ee40 ... G_9395.jpg

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Re: Sand Mold Basics

Postby Bert Weiss » Sun Jan 20, 2013 12:41 pm

One thing I have learned is that there is a wide range of recipes and techniques that might work. There are a few basic things you need to get under control. First is the mix of particle sizes you are using. All fine powder tends to have no push back strength. A mix of large and small particles is the best approach. Since sand sticks to glass, these particles need to be coated with fine particles that don't stick. If there are enough separating particles in your original mix, you don't need a subsequent dusting. Some mixes are quite durable and some will begin to leave scum on the glass.

Remember that sand has a high mass, so the more sand you put in the kiln, the more it costs to heat it up, and the longer it takes to cool down.

There are also a myriad of ways you can devise to create shapes and textures using any refractory materials, fibers or particles. You will soon find that some approaches work better than others.
Bert



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