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I know most of you slump and fuse on kiln shelves, but I am wanting to use a sand base. I have done an archive search on using asand base and did not seem to come up with much. Do any of you use a sand base? and what do you use.
I have got some information on a basic sand mix which is:
6 parts jointing sand
1 part alumina hydrate or bentonite
1 part casting plaster
1 part kaolin powder
Is anyone familiar with this mix?
i know that the design in the sand will be flattened by the weight of the glass but it is minimal. I used to work for a firm who use this type of bed.
thanks.
John

John I would check out the second item i.e. one part alumina hydrate or bentonite could this be a mistake? as the alumina h' is refectory. and bentonite (volcanic ash) be is a very plastic clay that's would bind the sand.. so I would say the bentonite may a sub for the kaolin .. but I could be wrong...Colin over on the other side of Oz

Mmmm. I don't know weather they used kaolin but they definately use alumina hydrate. they have just moved across to bentonite because the glass comes out clearer. ( I'm talking about clear glass only)
John

hi john, after that mix was fired on, did they throw it away or put in more plaster/clay/alumina ? it seems to me that those parts would get 'worn out' after a fuse temp fire. what temps were their top temps? i really want to try this. thanks, rosanna

John wrote:Mmmm. I don't know weather they used kaolin but they definately use alumina hydrate. they have just moved across to bentonite because the glass comes out clearer. ( I'm talking about clear glass only)
John

As I said I could be wrong and it looks like I was this time...as I also work in pottery bentonite is quite plastic used in glazes for suspension .I have just had a look at the chemical formula and it could be very refectory when used in the amount that you quote.in pottery it is used as a glaze suspension agent and only 1 or 2 % would be used .. being volcanic ash it contains silica and alumina and at the temperatures used for glass slumping it will be as alumna very refectory... IN SHORT I GOT IT WRONG

Colin

I am always interested in the idea of a casting sand. I use alumina hydrate, plaster, and diatomecaeus earth.

I recommend against kaolin because after being fired above 1400 it leaves scum on the next firing.

In general sand sticks to glass. Hot glass casters use olivine sand (available from foundry suppliers) with a little bit of bentonite because it is silica free and less toxic. It still sticks. When hot casting, you coat the sand with carbon to make a release. The problem with that program in the kiln is that you are likely to burn up the carbon because it has to be heated along with the glass.

Let us know how your experiments turn out after a few tries.

Bert
Here's something I do with olivine-
It's true that at about 500 F carbon black burns off-I mix a face coat of olivine with molasses. I use this against the form (about a 2" layer) then back that up with just the olivine and bentonite. I put it all in the oven and take it up to 1000 F (after the form is removed of course) on the way up the molasses burns out causing a 2" thick layer of carbon-It sure makes the studio smell good!! Then I ladle into the sand and anneal. These are pcs that could be 200 + lbs. so it's allot easier to do them in the oven then take the whole thing out with a lift.
Before that I would just preheat to 500 and cast but after the first ladle the carbon burns out and the pc. is clean and then sandy and requires sandblasting.
Keith

rosanna gusler wrote:hi john, after that mix was fired on, did they throw it away or put in more plaster/clay/alumina ? it seems to me that those parts would get 'worn out' after a fuse temp fire. what temps were their top temps? i really want to try this. thanks, rosanna

Rosanna, they use that mix for about 4-6 months just topping the mix up after each firing. the max tempreture they reach is 775 deg C. before each load of glass is put in you sprinkle alumina over your pattern to stop the sand fromm sticking too much. After the firing pick your glass up and with a stiff/hard brush wipe off the sand that has stuck. When you've done that wash the glass off and with a steelo (scrubber), rub off all the sand that has stuck. this may need a tube of elbow grease. generally when i had to clean off the glass it wasn't to hard to get off.
I am going to see an old colleague this week for more info.
Sorry it is a bit of an epic.

John

hi john, thank you for the 'epic'. one more Q, was the mix damp wet or dry when the impressions were made? it is good to get info on this subject fron someone who has some first hand knowledge. rosanna

The mix is completly dry. you neen to level the bed out after each firing,any low points just add more mix. Then get a concreters trowel and glide that over the suface to smooth it out the surface goes extremly smooth, but the base is light and sort of fluffy when you draw your design in the sand. Use your finger or a piece of wire for lines, a rod with a ballbearing gives a semi hollow effect, a greeware item like shells and starfish impressed into the sand look great too. the possibilties seem endless.

John

OOOEEE this is gonna be fun! i have everything on hand but the bentonite. will order that today. i assume jointing sand is just clean silica sand? the kind i would use in cement? sure am glad i bought that used glass kiln. this would be a pain in the big scutt. rosanna

Keith Clayton wrote:Bert
Here's something I do with olivine-
It's true that at about 500 F carbon black burns off-I mix a face coat of olivine with molasses. I use this against the form (about a 2" layer) then back that up with just the olivine and bentonite. I put it all in the oven and take it up to 1000 F (after the form is removed of course) on the way up the molasses burns out causing a 2" thick layer of carbon-It sure makes the studio smell good!! Then I ladle into the sand and anneal. These are pcs that could be 200 + lbs. so it's allot easier to do them in the oven then take the whole thing out with a lift.
Before that I would just preheat to 500 and cast but after the first ladle the carbon burns out and the pc. is clean and then sandy and requires sandblasting.
Keith

Keith

Do you think that the carbon from the molasses would hold up for a kiln carving firing to say 1365 F? I can see that the alumina interface would help, but not exactly 100 percent.


My kiln setup would be good for hot casting in to if I only had room for a furnace in my shop. I can roll the top away leaving the raised floor to cast in to. Some day maybe.

hi john, one more Q(i promise). were those proportions by weight or volume? thanks, rosanna

Rosanna, the amounts are by volume. If you can wait until Friday (AUS time)I will have some more information on what they are using now. Exact amounts etc. then you can be sure it's right. I may even some tempretures and times.

John

thanks john yewbetcha i can wait. wont have my bentonite untill next week anyhow. thank you so much, rosanna

Dear John,

I'm using one part plaster and one part alumina for "sand" slumping. It works for me.

For background designs we use textured rubber paint rollers or rubber mats.

Rubber mats comes in sizes of 12" square to 48" x 72"

Hope this helps

Nelson