This has excellent plasticity. Use it for rolling refractory slabs or forming other shapes. Dry pieces evenly to prevent warping during drying.
This is the product of a series of tests that had high alumina percentages. But did not have good thermal shock resistance (this adds Kyanite aggregate to improve that) and whose working properties were not robust enough (thus the 30% added ball clay). The bentonite augments the plasticity. The barium precipitates solubles salts during drying.
This recipe compromises the service temperature but the body should still be plenty refractory enough for any common purpose.
In Nov. of 2018 Joe mixed up a 2.5 Kg. batch of dry powder and yielded about 3 Kg. of pugged clay that would be of a consistency comparable to our pugged clays, perhaps slightly softer. A 1500 gram piece of this clay was used to roll out a slab 1/4 thick with rods in the studio for a kiln shelf that would be the size for the lab test kiln ConeArt BX 119D. A dried shelf of this size weighed about 835 grams prior to being fired in the kiln.
This produces a super-refractory powder layer that stays in place and does not harden excessively after many firings, does not chip or cake, that does not shrink and crack. Because it contains gum it paints on very well, staying wet long enough to level and even out with a brush. Also useful as a refractory ceramic coating.
Zircopax is among the most refractory materials in ceramics, so it was chosen to form the bulk of the dry mix (calcined alumina could also be used). Calcined, rather than raw kaolin, was employed to help densify and stabilize the coverage (by its flat particle shape). Laguna gum solution was added to harden the dry layer and slow down the drying (their gum solution has a higher percentage of CMC than achievable using common mixing methods). The slurry produced is a little thin, but it paints evenly onto even on absorbent alumina shelves, especially with a small paint roller.
This produces enough to fill a pint jar. The Laguna gum solution has 6.6g CMC Gum per 100g. It is a little difficult to mix in the final amount of powder yet a thin paintable slurry is produced (a good propeller mixer it needed). Specific gravity: 1.87. Approximate retail cost: $7.50. One pint coverage (single-coat): Nine 12 x 24 gas kiln shelves (about 18 square feet).
We continue to have issues with the slurry settling in a hard layer (epsom salts was used in initial testing but it did not prevent settling and the slurry developed a rotten smell). Calcium chloride addition of approx. 2 grams added to see if this would keep mixture in suspension, worked for a few days, but returned to hard-panning. It is very difficult to mix back up at this stage. (pure calcium chloride ice-melting crystals are available at many stores; it is also used in cheese-making and brewing and is available at amazon.com). However once the hard material is stirred back in it works normally, and the benefits outweigh this issue).
We also added 1 gram of Dettol to this mixture to alleviate rotten smell, and this has worked well over time, but the kiln wash now definitely smells like Dettol.
L4001 Kiln wash (left) vs. typical kaolin:silica wash (right)
The new wash has been fired on and is adhering well, not shrinking or cracking and is not powdery. The layer is much thinner. The other side has been fired many times and the flakes stick to the foot rings of every piece fired in the kiln.