aluminum oxide

[Bert Weiss]

has anybody used aluminum oxide as a sand casting material with sheet glass? Does it stick to float glass around 1500ºF?

I am working on developing a better sand casting recipe than 80% sand/20% plaster.

[Lauri Levanto]

Hi Bert,
in my molds I have used plaster+AlO as a splashlayer.
I have used it with float for slumping, but also with
soda-lime glass for casting.

The glass I cast is pint from a local glass factory. It is veru
short glass, much like float.

Plaster+ AlO 1to 2 ratio does not stick in flowerpot
casting temperature 950 C.

My last experiment (still in the kiln) was a plaster+kaolin
mold which I lined inside with plaster plys aluminium oxide.
I made a watery mix, filled the dry mold with it
and poured out in 30 secs. This leaves an extra smooth
thin layer of aluminium oxide to the mold surface.

-lauri

[Brian and Jenny Blanthorn]

has anybody used aluminum oxide as a sand casting material with sheet glass? Does it stick to float glass around 1500ºF?

I am working on developing a better sand casting recipe than 80% sand/20% plaster.

U may like 2 try zircon might B zircon oxide or something

Got a real high melt temp

As a spray on coating / splash coat

I think the blowers use carbon from a flame as a coating

U might try Ur Q over craftweb

Brian

[Bert Weiss]

Hi Bert,
in my molds I have used plaster+AlO as a splashlayer.
I have used it with float for slumping, but also with
soda-lime glass for casting.

The glass I cast is pint from a local glass factory. It is veru
short glass, much like float.

Plaster+ AlO 1to 2 ratio does not stick in flowerpot
casting temperature 950 C.

My last experiment (still in the kiln) was a plaster+kaolin
mold which I lined inside with plaster plys aluminium oxide.
I made a watery mix, filled the dry mold with it
and poured out in 30 secs. This leaves an extra smooth
thin layer of aluminium oxide to the mold surface.

-lauri

Lauri

What particle size are you using? The stuff I am about to purchase is 120 mesh for sandblasting grit. It sounds to me like you are using a finer particle size. I guess I'll find out if it works.

[Bert Weiss]

has anybody used aluminum oxide as a sand casting material with sheet glass? Does it stick to float glass around 1500ºF?

I am working on developing a better sand casting recipe than 80% sand/20% plaster.

U may like 2 try zircon might B zircon oxide or something

Got a real high melt temp

As a spray on coating / splash coat

I think the blowers use carbon from a flame as a coating

U might try Ur Q over craftweb

Brian

Brian

I took a hot sand casting class at Pilchuck. We used carbon from an acetylene torch as a seperator. That carbon would burn off in a kiln environment, before it did it's work.

A couple of weeks ago I did some kiln sand casting using some sandblasting grit from Dupont. It contained several minerals including zircon and silica. It only stuck a little plain, and mixed with plaster and dusted with plaster, it did very well.

I think I'm on to some good directions. It is obviously new territory because there were lots of looks and few responses.

[Lauri Levanto]

Good news, Bert

The piece where I tested "slip casting" a layer of
AlO+ plaster came out beautifully.
The coatong did stick, but was easy to wash off
with a soft sponge and water.

The piece has a frosty look, with slight satin gloss.

I do not know the grit of my AlO.
It is really fine, feel smooth like starch between finges.
The finish seems like polished with 400 grit diamond pad.

Please note, this stuff seems to have quite
high thermal capasity or low thermal conductivity.
The piece was badly undeannealed.

-lauri

[Jim Murphy]

Hi Bert,

Instead of Alumina Oxide, is there any reason to discount using Alumina Tri-Hydrate (325-mesh) along with plaster as your sandcasting "mold" for sheet glass ?

I'd think proper (slow) firing of the Alumina Tri-Hydrate + Plaster "mold" would release the extra chemically-combined water and may lead to a smoother glass finish.

Jim Murphy

P.S. Haven't tried sandcasting myself

[Bert Weiss]

Hi Bert,

Instead of Alumina Oxide, is there any reason to discount using Alumina Tri-Hydrate (325-mesh) along with plaster as your sandcasting "mold" for sheet glass ?

I'd think proper (slow) firing of the Alumina Tri-Hydrate + Plaster "mold" would release the extra chemically-combined water and may lead to a smoother glass finish.

Jim Murphy

P.S. Haven't tried sandcasting myself

Jim

I already use flour of alumina hydrate and plaster as a mold former. I'm looking for a larger particle that can hold a pattern better.

I ordered some olivine sand and some aluminum oxide both 100/120 mesh.

[Brian and Jenny Blanthorn]

[/quote]

Jim

I already use flour of alumina hydrate and plaster as a mold former. I'm looking for a larger particle that can hold a pattern better.

I ordered some olivine sand and some aluminum oxide both 100/120 mesh.[/quote]

How U forming this mould / pattern

There is always a problen n advantage of technology transfer from hot glass 2 warm n visa versa

I think olivine sand has some kinda binder in it like oil

So gass may B a problem

The binder or whatever is 2 give form strength while hot casting

U may B able 2 replicate this with

Normal sand + say 10 - 30 % china clay ( or plaster ) + poss bit gum arabic

Mix this damp then warm to dry off

Poss then spray with china clay / alumina a soft mix say 40 / 60

Dry of again n fire

Keep temp low fire slow / soak

I am just guessing here

Brian

[Gale aka artistefem]

Bert......is it the weight of the large glass expanse/loss of 3-d texturing that you're trying to combat?

You may already be starting here, but what about cutting the design pattern out of fiber blanket? Layering it to form the 3-d base, then spraying or sprinkling on the sand mixture on top of the fiber form?

Do you want a sand imprinted surface or a smooth surface? With this fiber blanket cutout method, you might be able to use a large particle sand size to create the more textured appearance. Do you also want some of the sand particles to stick to the glass or are you going for a complete clean release?

[Bert Weiss]

Brian

For hot casting, the olivine sand was mixed with bentonite and water, then sifted and pressed to get the form.

The recipe I was given for kiln casting was 80% sand/20% plaster. Obviously used dry.

Olivine sand is primarily magnesium sand so there is no free silica involved.

The plaster is there to coat the sand and keep it from sticking. Clay isn't there so that the mix can be used over and over, being fired over 1400ºF

The idea is just to screed out an inch or so of sand on the kiln floor and press stuff in to it. The mix I have been using is not very strong relative to holding much detail. This will be much better.

The Aussies have been using this technique for a while now. They use beach sand. I think that I can make a more interesting particle mix with some experimentation.

Of course the important aspect is what you do for the pattern.

My absoulute favorite art glass made with this technique was posted on the BB a long time ago. It was done by aboriginal artists way in the outback with the collaboration of a glass artist who's name escapes me. My head still spins with the wonderful imagery they did.

[Brian and Jenny Blanthorn]

Brian

For hot casting, the olivine sand was mixed with bentonite and water, then sifted and pressed to get the form.

The recipe I was given for kiln casting was 80% sand/20% plaster. Obviously used dry.

Olivine sand is primarily magnesium sand so there is no free silica involved.

The plaster is there to coat the sand and keep it from sticking. Clay isn't there so that the mix can be used over and over, being fired over 1400ºF

The idea is just to screed out an inch or so of sand on the kiln floor and press stuff in to it. The mix I have been using is not very strong relative to holding much detail. This will be much better.

The Aussies have been using this technique for a while now. They use beach sand. I think that I can make a more interesting particle mix with some experimentation.

Of course the important aspect is what you do for the pattern.

My absoulute favorite art glass made with this technique was posted on the BB a long time ago. It was done by aboriginal artists way in the outback with the collaboration of a glass artist who's name escapes me. My head still spins with the wonderful imagery they did.

Paul Sanders

A site he is on + some Aboriginal artists

http://www.tjulyuru.com/gallery.asp


The original gallery U may find it in tour archive

http://www.tjulyuru.com/gallery.asp



Original thread

http://www.warmglass.com/cgi-bin/wgarch ... read=13234

Enjoy

If U wann a look, these tours take a while 2 load

Brian

[Jim Murphy]

Bert,

Thanks, I understand now. If the larger Alumina Oxide doesn't satisfy your need, there is another material you may consider adding to your recipe that may help to hold a pattern better - 200-mesh Kyanite.

Kyanite has many uses, including refractories for glass. Kyanite is well-known for its interlocking property, due to its needle-like shape of the Kyanite particles, which provides for mechanical strength.

Raw Kyanite may expand upon heating. In general, the larger particles expand more than smaller which is why I suggest using 200-mesh. Should be available at your local ceramic supplier.

Best wishes,

Jim Murphy

[Bert Weiss]

Paul Sanders

A site he is on + some Aboriginal artists

http://www.tjulyuru.com/gallery.asp


The original gallery U may find it in tour archive

http://www.tjulyuru.com/gallery.asp



Original thread

http://www.warmglass.com/cgi-bin/wgarch ... read=13234

Enjoy

If U wann a look, these tours take a while 2 load

Brian

Great stuff!! Thanks Brian

[Nelson Tan]

"The idea is just to screed out an inch or so of sand on the kiln floor and press stuff in to it. The mix I have been using is not very strong relative to holding much detail. This will be much better.

The Aussies have been using this technique for a while now. They use beach sand. I think that I can make a more interesting particle mix with some experimentation. "


Bert

I went to Sydney Australia March of this year and visited a stained glass studio that also makes slumped float glass.

The guy uses red brick sand for his projects. A bed of red brick sand is first fired to remove any moisture trapped. Then he pressed the shells, starfish or any other object into the sand. Afterwards he would sprinkle some plaster. Then fire.

Nelson

[charlie holden]

Alumina Oxide is better than plaster in terms of its release from the surface. Zircon is better yet. Warren Langley, (an Aussie), use Aluminum Oxide sifted on the surface of the sand/plaster mix when he wants a cleaner release than he gets with sifted plaster. He sifts before he makes the impression. When he wants really sharp edges, and distinct transitions from flat areas to slumped details, he goes to cut out fiber paper.

I think that the packing issue is more one of mixes of particle size and sharpness than it is of refractory qualities. "Mixing It With the Best" talks about packing with large, medium and small particle sizes. I think you're going to find 120 grit is too big. Maybe combined with plaster you'll get the three different sizes.

Olivine sand, (which is, I think, Magnesium Silicate), is sharper than silica sand, so may hold an impression better. (Olivine comes in three different mesh sizes which seem much finer than standard grits. 100 grit Olivine seems like 220 or higher to me. I don't know what that's about.) You could also try adding about 7% Bentonite and misting it with water once you have the impression. It will get pretty hard and hold up to heating in the kiln, but you may have to sift it out of the bed after each firing.

The binder that Brian mentions is in a product called Petro-Bond. It is a sand with oil mixed in. Used in hot casting it takes a fine impression and releases from the glass like a dream. But the oil would obviously burn off in a kiln.

[Bert Weiss]

Alumina Oxide is better than plaster in terms of its release from the surface. Zircon is better yet. Warren Langley, (an Aussie), use Aluminum Oxide sifted on the surface of the sand/plaster mix when he wants a cleaner release than he gets with sifted plaster. He sifts before he makes the impression. When he wants really sharp edges, and distinct transitions from flat areas to slumped details, he goes to cut out fiber paper.

I think that the packing issue is more one of mixes of particle size and sharpness than it is of refractory qualities. "Mixing It With the Best" talks about packing with large, medium and small particle sizes. I think you're going to find 120 grit is too big. Maybe combined with plaster you'll get the three different sizes.

Olivine sand, (which is, I think, Magnesium Silicate), is sharper than silica sand, so may hold an impression better. (Olivine comes in three different mesh sizes which seem much finer than standard grits. 100 grit Olivine seems like 220 or higher to me. I don't know what that's about.) You could also try adding about 7% Bentonite and misting it with water once you have the impression. It will get pretty hard and hold up to heating in the kiln, but you may have to sift it out of the bed after each firing.

The binder that Brian mentions is in a product called Petro-Bond. It is a sand with oil mixed in. Used in hot casting it takes a fine impression and releases from the glass like a dream. But the oil would obviously burn off in a kiln.

Thanks Charlie

I appreciate understanding a bit more about Warren's process. I wish I had been at Pilchuck with you.

I am wondering about the difference between alumina hydrate (kiln wash) and aluminum oxide (sandblasting grit).

My feeling is that I want to work with a range of particle sizes from coarse to fine. The more particles that don't stick, the better. I will avoid clay or moisture and work with plaster and alumina hydrate as my seperating layer.

I picture having a sand bed that can be used over and over, each time with a different pattern. I have been doing this with fine powders for many years. I am excited about the possibilities when larger particles are used.

One of the issues, although not really important to me in the long run is the cost of the various particles. Play sand from Home Depot or stolen beach sand are the cheapest. Aluminum oxide is about twice as expensive as olivine sand...

It looks like I'm making a trip to a foundry supply house next week to see what I can find there. Between there and a good pottery supply, I should end up with a good mix.

A couple of weeks ago I got to work with some Bohle casting materials that don't stick to anything but your wallet. They had a fine gray powder that was very nice and coarse gray particles that looked about the size of garden vermiculite but didn't stick. They made a cool contrast. The cost was way ridiculous though.

[Lauri Levanto]

Bert wrote earlier:
The recipe I was given for kiln casting was 80% sand/20% plaster. Obviously used dry.

If the setting time is no problem, you can use it wet.
The plaster is calcinated back to dry at ca.240 C.
Using wet, you form plaster chrystals within the sand.
That makes it bind better.

Someone also mentioned the grit of sand.
According to my (Finnish) sources, the casting sands
are of variable particle size, and rated
on the average size. So f.ex. 120 grit AlO has
max particle size of 120, while 120 grit
olivine sand has average grit size of 120, including
some coarser and much finer particles.

-lauri

[Bert Weiss]

Bert wrote earlier:
The recipe I was given for kiln casting was 80% sand/20% plaster. Obviously used dry.

If the setting time is no problem, you can use it wet.
The plaster is calcinated back to dry at ca.240 C.
Using wet, you form plaster chrystals within the sand.
That makes it bind better.

Someone also mentioned the grit of sand.
According to my (Finnish) sources, the casting sands
are of variable particle size, and rated
on the average size. So f.ex. 120 grit AlO has
max particle size of 120, while 120 grit
olivine sand has average grit size of 120, including
some coarser and much finer particles.

-lauri

Lauri

That is interesting. If you did use it wet, wouldn't you have to grind and resift after each firing to reconstitute the mix? And wouldn't it set up faster after the first time? Ludo (reused already fired plaster) sets plaster faster as I recall.

I picture using the lazy process of doing everything dry and reusing it over and over with minimum processing. I might find that to get some finer resolutions, I might need to do the more labor intensive techniques. Although my experiments so far have been positive using simple impressions. I'm going for big shapes, not finger prints.

I'm glad to hear about the particle sizes of the sand because the foundry supply house carries only 100/120 mesh olivine. I was thinking that I could get some 200 mesh particles at a pottery supply, either zircon or kyanite or something in that order. Plaster of course is quite fine. I also use diatomaceous earth in my mix, which is in the middle somewhere.

I appreciate everybody's input here. With some messing around, I should get a pretty good technique worked out. With any luck it will be worth the effort to improve on beach sand and plaster. When I first posted and nobody responded I got worried that I wouldn't get any good input. The WGBB world wide research team has come through in full color. Thanks

My next consideration is whether to try and contain the sand, in the kiln. Mostly I have worked with a "pile" of sand just sitting on the kiln floor. I can see the efficacy of screeding it flat, but this could be done using pine boards that are removed. The permanent alternatives are stainless steel angle iron or vermiculite board dams. I'll go simple and then work with a dam if I think it will be worth the expense and effort.

[charlie holden]

For screeding at Pilchuck we just used some one-by-twos laid lengthwise on the outside of the sand. If you want something more precise and permanent you could go to square tubing. I think Warren uses rectangular welded aluminum tubing frames. (He doesn't leave them in when he fires.)

He also had a trick of piling up a bunch of sand and using a piece of plywood with a curved profile cut out of it, and a rod attached to one edge as a center. He sinks the rod into the middle of the pile of sand, rotates the plywood around and forms a bowl mold. He then drapes a piece of float over it and fires it hot to get a funky bowl. Says he used to pay his costs with bowls when he was starting out.

Warren also said that he starts with about 20% plaster in his sand and uses it untill the amount of sifted plaster increases so much that he starts to lose detail in the impressions. Then he cleans it out and starts over. My bet is that he would consider recycling the old stuff by adding more sand too much trouble. One thing for sure about Warren, he's all about working fast and loose.