Cone 6 Black and Red Burning Casting Bodies

Coffee Clay Cone 6 Black Casting Body

Total:110.00

Notes

*This is part of a project to create a casting version of Plainsman Coffee Clay. It was built on a cone 10 porcelain base recipe. The umber fluxes it to mature at cone 6. It casts exceptionally fast and releases from the mold very quickly. Fired color is vary dark, almost black. To get a jet black glossy functional surface for beer bottles we glaze this with the GA6-B, a zero heavy metal glaze.

To make the slurry we use 100 clay, 40 water, 0.6 Darvan (e.g. 5000, 2000, 30 for about a gallon). The slip may be runny at first and gel later - add a little more Darvan if that happens.

This is not very plastic so there is a little tearing when trimming or cutting leather-hard ware (or when pieces shrink and pull away from the mold). When trimming mold seams at dry stage this is a little too powdery. To tune plasticity substitute a little of the Opticast with a plastic kaolin (e.g. #6 Tile).

Pictures

L4768A vs L4768D casting bottles

The L4768D fire shrinks more than the L4768A. And is not quite as black.
The difference in umber could be the issue.

L4768D & E vs Coffe Clay fired bars

M390 Cone 6 C-Red Casting #1

Total:100.00

Notes

*Another mix, L4558B is underway, stay tuned.

The previous work (as L4558) added 30% C-Red to standard M370 casting to try to achieve the red fired color of M390. C-Red is proving to be a valuable way to get red colors since it does not gel casting slips and it is very refractory (thus preserving red coloration). This improves on the work done with above by taking the M370 and rationalizing it as follows:

-M370 contains 1% talc, this removes that. Unfortunately maturity has been lost so the talc may be needed.
-M370 uses a highly plastic kaolin, ball clay and bentonite to target wheel throwing. This casting version removes bentonite but it still suffers long casting times because of the other two materials. This substitutes all three for Opticast kaolin. Casting performance is excellent.
-This approach offers flexibility in maturity, just reduce or increase the nepheline syenite.

It is important to remember that red color is achieved by the right body maturity (too high and it turns brown, too low and it looks like terra cotta).

Keep in mind that a clear glaze will turn a red-burning body brown at stoneware temperatures, that is a fact that must be lived with.

This deflocculates extremely well. Our first test batch used 4000g powder, 1680 water but the normal 30g of Darvan was too much (it is too thin). Still its casts very quickly. Actually, too quickly so it is really important to stay on top of the process to avoid getting the walls too thick.

Dry hardness is excellent.

Pictures

L4558A M390 cast bottle vs. L4768D

L4558A is not mature enough on the bottom of this slip castbottle. That being said it has plenty of firing shrinkage, so this is being heatsink by the kiln shelf.

L4558A M390 vs M390

Color is not red enough. This is likely a combination insufficient vitrification and insufficient iron oxide - I will make another mix to move it in that direction.

M390 Cone 6 C-Red Casting #2

Total:100.00

Notes

*This follows L4558A, it explored the merits of using the amazing ultra-high-iron C-Red clay from IMCO (which is also refractory and excellent for slip casting). It was a little too refractory and the color development was not sufficient. This adds more Nepheline Syenite and C-Red and sacrifices some silica and kaolin.

We are using Kaopaque kaolin temporarily until a shipment of Opticast arrives.

The original work added 30% C-Red to standard M370 casting to try to achieve the red fired color of M390. That produced a dark burning very mature body.

Pictures

L4558B red burning casting body vs M390

These were fired to cone 6.
The top one is M390.
The color of L4558B is very close now. These mugs and other pieces worked well with all glazes tested. No fired warping occurred.