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Calcined Kaolin? (Glomax)


Biglou13

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Alberta as far as I know is more like albany slipa darker clay ( is use a few bags each year in my black glaze) than a white EPK clay.

Its from Canada (Alberta) maybe they are are talking C not Fahrenheit- eh

I would not use it it for kiln wash-stick to whiter cheaper EPK

As far as driving mositure out 1000 degrees is fine.

When I calcine I just fill a green bowl up that needs bisquing and fire it with the rest of the load.

Mark

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Slip glazes can crawl or pop off in the firing. Using  about half calcined

(or more)and half raw in a slip glaze recipe will help eliminate that issue.

Many slip glazes with Alberta or Albany are almost all clay.

I try not to have more than 10% raw clay in may glazes with the balance calcined clay. For me 10% will keep most ingredients in suspension and not hard pan.

Wyndham

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I

Epk is my friend.

Just wondering cause mfg suggest to calcine Alberta slip to 1000F

Wondering if there is a technical difference.

Tomatoe tomato, potato potatoe.........

Dude! I almost spit tea out my nose!!

Alberta slip is a blended clay designed by Plainsman Clay out of Medicine Hat to be a substitute for Albany clay. It's very plastic, loaded with iron, and melts into a glaze by itself at ^10. Not ideal for kiln wash by any stretch. If you tried calcining it to 1000*c, well...it might be a bit more than calcined.

Some good fire clays and stonewares come out of my neck of the woods, but nothing really in the way of primary clays or kaolins. The deposits are too far away from the parent rock.

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The temperature for calcining any clays is flexible. Just throw some in a bisqued, unglazed bowl and include it in your regular bisque fire. Cone 07-06 ought to be hot enough.

Why are you calcining Alberta clay? Just wondering.

TJR.

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That makes it clear as that link above shows Alberta with a really low sinter point.Looks like you want to keep it low heat for that clay.

As I have never needed to calcine Alberta this is news to me.

mark

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Guest JBaymore

If you take a Z grams of dry sample of material X (that has something like a XCO3 or a H2O in the molecular structure) and then fire it to progressively higher tempeatures, stop heating it, and then weigh it again...... you can find the point or points where the particular reaction(s) you are looking for has/have been completed.

 

So in the case of calcining a clay.... where the MAIN constituient you are looking to change is clay to ceramic (drive off the chemically combined H2O) ....then you are looking for the temperature at which all significant weight change has happened. (carbonaceous material burning off will be in a lower range ... closer to 450-600 F) This change clay/ceramic is not an instatntaneous change... it happens with some heat work.... so there will be a range where it starts losing the weight of water molecules.... and a place where they are all gone.

 

The desired calcining temperature is just ABOVE that termperature, and below where the material will have to be re-ground (due to stuff like sintering).

 

best,

 

....................john

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Guest JBaymore

I

Epk is my friend.

Just wondering cause mfg suggest to calcine Alberta slip to 1000F

Wondering if there is a technical difference.

Tomatoe tomato, potato potatoe.........

Dude! I almost spit tea out my nose!!

Alberta slip is a blended clay designed by Plainsman Clay out of Medicine Hat to be a substitute for Albany clay. It's very plastic, loaded with iron, and melts into a glaze by itself at ^10. Not ideal for kiln wash by any stretch. If you tried calcining it to 1000*c, well...it might be a bit more than calcined.

Some good fire clays and stonewares come out of my neck of the woods, but nothing really in the way of primary clays or kaolins. The deposits are too far away from the parent rock.

 

 

That (kiln wash) is not what Wyndham was talking about ........ read again.

 

He's talking about calcining to stop excessive shrinkage in an all clay (or close to that) glaze.

 

best,

 

.......................john

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Regarding sintering. I bisque fired some epk "prill". Well they weren't crumbly to start, But definitely are much harder to crumble by hand after bisque. This was "un calibrated" 04- 05. It's an experiment for no pottery related things.

 

The Prills are all still separate, not a mass so by the definition not sintered. And nowhere near vitrified. I think I was in the 30% absorption rate.

 

This is prolly a John b? (This a pottery related?)

What is the inuslative value of epk as powder, as prill plus powder. Since calcined is technically "denser" I'd imagine the insulation value rises as calcined.

I can't seem to find the comparison of vermiculite, perlite either. It was info that compared fiber blanket, soft brick, hard brick etc.....

What about silica? Aka sand?

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Guest JBaymore

WHat you want to study up on is thermal conductivity of the materials as a starting point.

 

Thermal conductivity of most ceramic clays are VERY similar. Fireclay, kaolin, ball clay, eatrthenware clay.  All similar. 

 

For kiln refractoy purposes, the insulative value is from the dead air spaces created in the product.... not the material.  The material is what gives the USE TEMPERATURE RATING .... not the K (insulating) value.  A wall of earthenware clay and Kaolin clay will have about the same insulating value per inch.... but earthnware will MELT (due to flux cintent) when the temperature goes up.... and THAT will change things fast.

 

Yeah....... Kaolin is quite refractory.... but has little insulating value.  Ditto silica sand.

 

What makes fiber so good is the lack of thermal mass .... not the astronomical insulating value.  The insulating value per inch is not all that much better than insulating firebricks.  It is just that you are storing almost no heat energy in rasing the refractory mass up to the kiln's temperature.

 

Vermiculite and pearlite will melt at stoneware temperatures.... making the lining fail.  OK for lower temps ... as backup only. 

 

Saswdust will burn and leave dead air spaces... but also leaves a bit of ash.... which is a source of flux (CaO) at high temperatures.

 

There is a reason that commercial refractories work well.... industry knows this stuff.  You get what you pay for.

 

best,

 

...............................john

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Thank you as always you answers give much to study. More food for thought.

 

My idea was using the calcined epk Prills, ( epk is pretty much local for me) as insulating layer, on the outer side of hard brick, maybe part of floor layer.

 

Thinking alternative to 9 inches of brick and capping material.

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  • 2 weeks later...

TJR, because that is what is suggested by alberta slip on the website / plaimsman clay.

 

http://plainsmanclays.com/albertaslip/index.php?preparation=1

 

 

 

 

I am about to do some mixing and testing of Alberta slip glazes which include, in part calcined slip , and I see the instructions on the Plainsmanclay website says: "We fire them (clays) to 1000F (Cone 022 or red heat) at 100F per hour and hold for 10 minutes.."  Firing up for 10 hours seems a little extreme. Does anyone think that is necessary?

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I just re read directions.

I'm not following directions.

My glazes are fine.

I've fired in small bowls and a small and medium saggar. The color change is similar to pictures. And it holds dry inside 5 gal bucket sealed (I live in high himidity area). No problems. My technique may be off bit the Results don't lie. Eg. Falls creek shini aka Randy's oatmeal rust

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I'm planning on patch work of brick for non support areas of floor eg walls. so Prills aren't fully responsible bearing load.

 

I'm short on bricks, and am thinking outside of box.

 

I'd love to use IFB.

 

As far as kiln sized structures go are ifb and hard brick Load bearing ability similar..

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Guest JBaymore

As far as kiln sized structures go are ifb and hard brick Load bearing ability similar..

 

Nope. Look up the "cold crushing strength" and "hot crushing strength" for each. It is a listed property.

 

Hardbrick for working kiln floors is also an issue of the physical abrasion that typically happens there....... particularly if you are walking on it, or throwiong wood into it. Plus the resistance to drips of crap.

 

I have built wood kilns where the floor was simply a rammed layer of straight (OLD) AP Green dry milled 30 mesh fireclay about 9-10" thick. It works. Not much insulating value.....like using hardbrick. Plus is shrinks when fired in place. B ut for a "low tech" kiln... it CAN work.

 

If you are building a long firing wood kiln right into the gtround.... prep the foundation site well. You can catch underground roots on fire if they grow into the zone of the foundation.

 

best,

 

...............john

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