aluminum oxide

[jerry flanary]

What about a spray graphite for a release?

[rosanna gusler]

isn't graphite basically carbon? if so, given our ramps, wouldn't it just burn out before process temps? rosanna

[Lauri Levanto]

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.

Now I see your point. After being above ca. 700 C both dry
and wet plaster are luto ( calcium oxide, no more sulphate)
You are right, the wetted luto needs to be grinded.

The container question:
Isn't it easy to make a ceramic flat saggar
( or use a kitchen oven pan for test)
fill it with the sand and lift off the kiln when not needed.
I prefer ceramics because the elements in my kiln are not
protected.

The idea is that you can put the saggar on stilts
so that the heat capacitance of the shelf does not
extend annealing time.

-lauri

[Brian and Jenny Blanthorn]

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.

I have had the lab people work on this some

As Marty is not so famous anymore

I have reassigned some of the security staff over 2 research

They insist on looking 4 plots in everthing to

Hydrate with water Al (HO)3

Aluminun oxide is Al2 O3

I use calcined which I understand 2 mean heated up so water is driven off

Looks like Al2 O3 is actually calcined alumina

ALUMINA, HIGH-PURITY

http://www.bnp.com/cgi-bin/ci/Mat_Search/db_search.cgi

Home page

http://www.ceramicindustry.com/CDA/BNPH ... 3,,00.html



http://www.baileypottery.com/clay/about ... em.htm#Raw


There is a few other chemical links here

http://talk.craftweb.com/showthread.php?s=&threadid=634

I think the stained glass people use whiting, then just keep re using it

But I dont know the temps it will go 2



While ur sorting this out go 4 something that is not dusty or unduly toxic

Although it apears that any dust is not a lot of good

I am not shure if U said but U can get aluminum oxide sandblasting grit in a varity of grits

Brian

[Bert Weiss]

I think the stained glass people use whiting, then just keep re using it

But I dont know the temps it will go 2

While ur sorting this out go 4 something that is not dusty or unduly toxic

Although it apears that any dust is not a lot of good

Brian

Whiting sticks at fusing temps. The stained glass painters work around 1250ºF.

I understand from Greg Rawls that alumina is nuisance dust not toxic dust. Common sense avoidance is necessary.

[Tom White]

Bert, I don't know if this would help but this is what I have done to get a cracked ice texture on 8" x 12" trays from 6mm float. I mixed 50/50 kaolin and alumina hydrate from ceramic supply store to thick paste (drywall mud). I troweled this onto kiln shelf 1/16" to 3/32" thick, dried and fired to full fuse. I then scraped it off and broke large plates to sizes desired. I place generous layer on kilnwashed shelf and place 6mm float over it and fire to full fuse, 1550 to 1575 F in my cramic kiln with borax on top and edges and aneal. Picture is available at http://f1.pg.photos.yahoo.com/ph/tomwhi ... pg&.view=t
I get clean release from glass. Any particles embedded by undercuts pop out easily. You might be able to crush this to desired particle size and mix with other size powders you are using now. I have used this 15 -20 times and get excelent results each time.

Best wishes,
Tom in Texas