Carbo Kaolin testing

Project Name

Carbo Kaolin Evaluation

Project Codenumber

UnAssigned

Notes

Of course, compared to our sedimentary clays, this material is very white and pure. But how does it compare to other kaolins we use?

Note that we process all test using slurry methods, by our standards it has a small percentage of oversize. But the ability to process this material as a powder is an unknown. It would like be very fluffy and difficult to screen, for example.

#6 Tile
It appears to be more plastic while having less drying shrinkage. It does not fire as white. However, our customers would likely accept the slighly darker color this would bring to M370 if it meant better plasticity, consistency and lower price.

Pioneer Kaolin
This is far more plastic.

Grolleg, NZ, EPK Kaolins
These are white burning, low plasticity, very sticky and good at suspending slurries. As pure materials they are all "swamp muds", gross to work with and needing lots of bentonite to make them usable.
Carbo kaolin is nothing like that, it is a plastic and ball clay like in workability. It has so much bentonite that dewatering the pure slurry takes hours on a plaster table.

EPK
Glaze recipes that specify EPK mostly do so out of tradition. In some cases it is chosen for the thixotropic character it adds to the slurry. Grolleg and NZK are both superior in every way we know of (including thixotrpic properties). Actually, no glaze slurry is going to be ruined by substituting a kaolin if a little attention is given (e.g. Pioneer Kaolin can work just as well as EPK if one includes some Epsom salts to gel the slurry).
In clay bodies EPK is a pain (because of variability and poor plasticity). A more plastic material is far more preferable. It is true that these don't fire as white, but EPK needs bentonite to augment the plasticity, and the amount needed with darken the color anyway.

Carbo Ceramics Kaolin Sample

Notes

*Received a one gallon pail of powder from
Jim Bevill, 478-943-2500
Carbo Ceramics Inc, 2295 Wriley Rd
McIntyre, GA 31054
Jim is at 478-737-2277

We are comparing this with #6 Tile kaolin for plasticity and firing behavior by itself and in a porcelain body.

Very slow dewatering on the batt. That is very unusual for kaolin and indicates high plasticity.

Drying shrinkage is very low given the degree of plasticity. This is a highly desirable property for use in porcelains as it enables coupling of high plasticity with good drying properties.

The sieve analysis was done by wet washing (after slaking).

Pictures

L4703 Carbo Ceramics Kaolin - Slurry

Lots of dark flecks (these proved to be both carbonaceous iron-bearing material). But these do not affect the texture, the soft clay is smooth despite significant +60 mesh particles.

L4703 Carbo Ceramics Kaolin thrown form

Throwing indicates very high plasticity, on parr with #6 Tile, the most plastic kaolin we know of.

L4703 Carbo Kaolin fired at cone 11 oxidation

Some iron particles are clearly evident.
The piece has not cracked or laminated as kaolins normally do, likely because of the particulates present.

L4703 Carbo Ceramics Kaolin vs Tile#6 kaolin

Fired at cone 11 oxidation. Two specimens of tile #6 are shown (it has some inconsistency shipment to shipment as can be seen by the colors of these bars).

The firing shrinkage is dramatically less than #6 Tile, indicating this is a more pure theoretical kaolin. Of course, the airfloated version could have higher shrinkage.

L4703 Carbo Ceramics Kaolin +40 mesh

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IMG_5315

Carbo Kaolin +100 mesh oversize particles

Notes

*This is to concentrate the impurities to be able to view how a high concentration of oversize particles exhibits in firing at various temperatures. Photos will be included when firing is done.

This was done by washing a slurry through a 100 mesh screen. Strangely, the oversize part was plastic enough to form easily.

Pictures

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Carbo Kaolin M370

Total:99.54

Notes

*This tests the Plainsman M370 recipe using this material instead of #6 Tile kaolin. Carbo was sieved to 140 mesh and ball milled for 1 hour.

Plasticity is as good or better than M370. This much plasticity would be undesirable in non-ceramic applications but it is fantastic for use on porcelains.

Drying shrinkage is quite a bit lower than M370, this is obviously desirable. But further testing would be needed to confirm the water content was the same.

Final firing at cone 6 produced excellent results with mugs. No fired speckle, good glaze fit, bright coloured glazes looked identical to the standard M370. However body colour fired a little darker - so this has higher Fe2O3 content.

However the firing shrinkage is higher than M370 (indicating better vitrification). That means the talc might not be needed if using this material instead of #6 tile.

Of course, it is not known how representative this sample is of shipments production would receive.

Pictures

L4703B Carbo Kaolin freshly thrown pieces

I sieved out +140 particles and balled the under size to use this as the kaolin in the recipe (about 40%).
Attaching handles, trimming and drying are all good.

L4703 M370 using Carbo Kaolin

Left: L4703
Right: M370
Glaze is G2934 red.

L4703 M370 using Carbo Kaolin

Left: Carbo Kaolin M370
Right: Standard M370 using #6 Tile kaolin.

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L4703B Carbo Kaolin vs L4255D

The Carbo porcelain (left) produces a brighter purple color than any other porcelain we know even though others fire whiter. The piece on the right is not porcelain but is a demo of how poorly the purple glaze performs on some bodies.