bentonite for sand casting

Bert Weiss · Post by **Bert Weiss** » Mon Jan 19, 2004 10:51 pm

I have read here that bentonite can be mixed with sand as an alternative to dry plaster. I have had great results using olivine sand and plaster.

i was speaking with a foundry guy today who told me that he thought that an olivine/bentonite mix would need 5% water to work right. he thought that the water was needed to disperse the bentonite around the sand.

I don't picture that the moist pac would be good to use for kiln fired glass.

Can anybody tell me about how they use the bentonite for kiln casting. Is it good as a seperator dusting?

Brock · Post by **Brock** » Mon Jan 19, 2004 10:56 pm

That Olivine/Bentonite/water mix is what is used for sand casting with molten glass. Haven't used it in a kiln. Brock

rosanna gusler · Post by **rosanna gusler** » Tue Jan 20, 2004 7:57 am

aussie john was the one that said he used it. he said dry. it is a fine powder. i have 25lbs of it sitting on the floor waiting for my spare time to show up. rosanna

rgm · Post by **rgm** » Tue Jan 20, 2004 12:43 pm

Bert
I did a casting workshop with Berteil V. some years ago and have his sand mixture on paper - will post if you need it but he adds only 5
percent bentonite well mixed into the sand .
Robert

rodney · Post by **rodney** » Tue Jan 20, 2004 1:26 pm

Robert Middlestead wrote:Bert
I did a casting workshop with Berteil V. some years ago and have his sand mixture on paper - will post if you need it but he adds only 5
percent bentonite well mixed into the sand .
Robert

,,,,,,,,,,,,,,thanks robert, would you kindly send the info on what berteil v. does with this

is the water in the mix for the molten glass used to prevent the side wall of the sand from caving in,,,,,,if a persons uses a sheet of glass, what keeps the tops of any peaks from becoming flat

once the process is complete, is there ever any need for cold working, is there any sticking

thanks
rodney

Bert Weiss · Post by **Bert Weiss** » Tue Jan 20, 2004 5:53 pm

Robert Middlestead wrote:Bert
I did a casting workshop with Berteil V. some years ago and have his sand mixture on paper - will post if you need it but he adds only 5
percent bentonite well mixed into the sand .
Robert

I too took sand casting with Bertil V. and Paul M. Kiln casting is a different animal.

rgm · Post by **rgm** » Tue Jan 20, 2004 9:17 pm

So it is - guess I have to read every word more carefully .

charlie holden · Post by **charlie holden** » Wed Jan 21, 2004 11:48 am

Robert Middlestead wrote:Bert
I did a casting workshop with Berteil V. some years ago and have his sand mixture on paper - will post if you need it but he adds only 5
percent bentonite well mixed into the sand .
Robert

Robert,

I'm interested in what Berteil uses for the negative forms in his pieces. This is for hot casting. He pre-forms some sand mixture, often into heads and faces, and places them into the bottom of molds to make a negative space. Do you know what he uses for this?

We tried using sodium silicate bonded sand last summer at Pilchuck but it turned into hard rock during annealing. The word was that his negative forms turn to powder during annealing. I've heard he may use some kind of oil bonded sand from the UK. Are you familiar with this?

Thanks, ch

Bert Weiss · Post by **Bert Weiss** » Wed Jan 21, 2004 5:52 pm

Charlie

We used 2 meshes of olivine sand and bentonite. I don't remember the percentages, but I probably have the notes at home (where I'm not).

First you sift the sand in to a box so that it is lofty. Then he presses in his large form, like the boat hull. Then he presses in objects. You could use anything from plastic toys to wooden carvings... Finally the mold is coated with graphite or carbon from an acetylene torch in places where he doesn't want the sand to stick. No carbon where he wants it to stick. Then molten glass is poured in, using a team of ladlers. As the mold fills up, he drops in objects made of compatible glass or copper foil. The whole box,sand and glass goes in to the annealer...

rgm · Post by **rgm** » Thu Jan 22, 2004 1:29 am

Berteils small negative pieces ie little figures do turn to powder after the
process but we didn`t make any during the class . He said someone
makes them for him in Sweden . Berteil has the luxury of working for
a large glass production co. so has many helpers . Someone emailed
me for his sand mix . He gave us two versions :
1/4 old sand
1/4 60 mesh
1/2 90 mesh
5 percent bentonite

Second version :
equal parts - 80 mesh and 120 mesh sand with 5 percent bentonite
A lot of time is spent mixing this stuff . He emphasized that .

Kevin Midgley · Post by **Kevin Midgley** » Thu Jan 22, 2004 4:30 am

Get an odd-job (that isd what it is called) Canadian made cement mixer for mixing mold materials. It is a small plastic barrel with baffles inside that is designed for a full bag of redimix cement. You dump in your materials lock on the lid and roll it across the floor. Works fast. They are under $40 Cdn. Kevin in Tofino

rgm · Post by **rgm** » Tue Jan 27, 2004 1:25 am

Does anyone have Warren Langley`s exact sand mixture for kiln
casting ?

Bill Grix · Post by **Bill Grix** » Tue Jan 27, 2004 3:39 pm

Hi Robert
I was in Warrens class last summer. his sand, plaster mix was 80% sand to 20%plaster.

Bill

rgm · Post by **rgm** » Wed Jan 28, 2004 12:09 pm

Thanks Bill - was that olivine sand ?

Lionel · Post by **Lionel** » Wed Jan 28, 2004 2:18 pm

80-10-10 sand/bent/water but you need to mull the hell out of it - I use my truck to run it over a few times. You also should use a steel frame and pack it with a ram. The mold has to be heated to 200 for about 8 hours to get all the water out before you charge or you will have big bubbles in your glass. Lots of torching helps for release.

http://home2.nikonnet.com/servlet/com.a ... emberguest

Bill Grix · Post by **Bill Grix** » Wed Jan 28, 2004 3:46 pm

Hi Robert
Warren said he uses any kind of sand, he like the differnt texures you can get. I use silica and get good results. No need for bentonite or mulling.

Bill