Cone 6 Black Burning Casting Body - Four ways to make one

Project Name

Black Cone 6 Casting Body

Project Codenumber

UnAssigned

Notes

This is a project to create a casting version of Plainsman Coffee Clay, a dark grey burning cone 6 stoneware. Black bodies do amazing things with glazes, that is the motivation.

There are three approaches:

1. Adding a black stain to an existing cone 6 powdered body (e.g. M340 or M370). Although expensive, this is the most foolproof approach, working for both stonewares and porcelains. The better the degree of vitrification the better the color develops. And the color bleeds through glazes very well.

2. Add umber to a cone 10 body (because the umber acts as a flux it reduces the firing temperature down to cone 6). This is less expensive. However, the color degrades with higher levels of fired maturity and does not develop well with lower ones.

3. Add umber to a body that already has a lot of iron. The advantage is that much less umber is needed and a darker color is achievable.

4. Make a body based on Barnard Slip.

5. Use a black engobe. Or a black stained slip that can be poured in and out of the mold before a lighter burning body. The L3954F recipe is a good start.

Cone 6 Black Clay Body - Type 1

Total:99.00

Notes

Plainsman 3B clay is a porcelain smooth cone 6 vitreous porcelainous stoneware, MNP. It hosts black stain very well, requiring a lower percentage to achieve black.

This is of course a plastic body. And you likely don't have access to the 3B. However, that clay can be synthesized using a 60:40 mix of ball clay and feldspar. Leave out the bentonite and the body should work well for casting, especially if you use KT#1-4 ball clay.

Pictures

L4053B black porcelain mugs

Glaze is GA6-C rutile blue.

L4053B black porcelain mug bottoms

L4053B fired bars

Cone 6 Black Casting Body - Type 2

Total:110.00

Notes

This recipe is built on a cone 10 25-porcelain base recipe. Previous tests indicated that umber would over flux even that to mature at below cone 6 (losing black color) so 5% Nepheline has been traded for kaolin.

While this version is not showing good color, there are suggestions below to improve it. That being said, this casts exceptionally fast and releases from the mold very quickly. We can be get a jet black glossy functional surface (using this for beer bottles) using GA6-B 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.

We did not take this recipe to the next step, but here is what is likely needed:
-Substitute some of the Opticast with a ball clay (e.g. 25 KT#1-4 ball clay, 30 kaolin). That will compromise the fast casting a little but improve green strength. Or using Pioneer kaolin instead of OptiKast.
-Reduce the Nepheline Syenite to about 15 and increase clay to 60 (to reduce fired maturity).

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 Coffee Clay fired bars

L4768D is at 25 Porcelain type recipe with 10% raw umber to stain it black (over fired to cone 7)
L4768E is based on mix of C-Red iron-stained clay and OptiKast kaolin (plus silica and feldspar) plus 5% raw umber.
Bottom bar is Plainsman Coffee Clay (cone 6)

Cone 6 Black Casting Body - Type 3.1

Total:105.00

Notes

This recipe is built around C-Red clay (plus enough silica so glazes fit, enough Nepheline to get to stoneware maturity and the rest being kaolin). The C-Red adds enough iron that only 5% umber is able to stain the body very dark grey.

Dry hardness is good, nice to trim and finish.

Mixed 5000, 2000, 38 Darvan. Had to add more Darvan and a little more water, after which it cast well and quickly.
This mix should work: 4000 powder, 1600 water, 34 Darvan (100:40:0.6).

Pictures

L4768D & E vs Coffee Clay fired bars

L4768D is at 25 Porcelain type recipe with 10% raw umber to stain it black (over fired to cone 7)
L4768E is based on mix of C-Red iron-stained clay and OptiKast kaolin (plus silica and feldspar) plus 5% raw umber.
Bottom bar is Plainsman Coffee Clay (cone 6)

L4768F Coffee Casting mug base at Cone 6

This version of the body was used to make a significant number of pieces (bottles, bowls, mugs, etc).
This recipe is similar to L4768E but drops Nepheline to 15 and raises C-Red to 30 and silica to 19. This was done to reduce fired maturity a little.

L4768F Coffee Casting with GA6-B

Even though the body does not fire jet black it really helps to darken this glaze (which normally fires a transparent honey color).

Cone 6 Black Casting Body - Type 3.3

Total:106.00

Notes

IMCO is making Guage Red as a substitute (C-Red is no longer available). If Guage Red works as well it will make this body possible: Dark burning and plastic yet deflocculating well.

This mix should work: 4000 powder, 1600 water, 34 Darvan (100:40:0.6).

Pictures

Typecodes

MAS-Master Ticket

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Cone 6 Black Casting Body - Type 3.3" id="256310" key="bJmtHXwk" date="2025-01-22" typecodes="MAS" codenum="L4768H" picturebasename=""> <recipelines> <recipeline material="OptiKast Kaolin" amount="38.000" tolerance=""/> <recipeline material="Silica" amount="20.000" tolerance=""/> <recipeline material="Nepheline Syenite" amount="12.000" tolerance=""/> <recipeline material="Guage-Red Clay" amount="30.000" tolerance=""/> <recipeline material="Raw Umber J4650" amount="6.000" added="true"/> </recipelines> </recipe> </recipes>

Born: 2012-11-29, Modified: 2025-01-22 21:57:08

Barnard Slip

Total:100.00

Auto Unity Formula + Mole%

Notes

Fired bars are very dark brown at cone 02 proceeding to black by cone 4. At cone 6 it is beginning to melt, indicating that the chemistry information here is not accurate, much higher fluxing oxide levels would be needed to create a material that melts at this low a temperature.

The clay is very non-plastic silty and very difficult to form test bars with. The high water content of the material, given its low plasticity, indicates a very small ultimate particle size.

This has the potential to be a base for a black burning casting slip body at cone 6 (with the addition of enough ball clay to suspend the slurry and impart enough shrinkage to enable pieces to pull away from the mold). Some silica might also be needed for glaze fit.

Pictures

REDART, Barnard, Alberta Slip decorated mugs

Brushwork is under a clear glaze.

L2626 Barnard Slip bars

Cone 6 Black Engobe

Total:105.00

Notes

This is the black version of L3954B White. Reduce the percentage of stain for less intense black.

Fires jet-black, much blacker than any black burning clay body on the market. Because particulate stain particles supply the color this is not messy to work with, just water will completely clean any surface (unlike black bodies made using raw or burnt umber). This will remove from clean plaster batt without leaving any stain.

We make a brushing version of this by mixing a 500 gram batch with 75g of Laguna Gum Solution and 280g water (fits 1 pint jar). It must be mixed in a kitchen blender to get the lumps out. It dries without cracking when painted onto an arborite surface and requires a metal scraper to get it off.

Pictures

10% 6666 stain in engobe under a clear glaze

Cone 6. M370.

10% 6600 stain bowl

Lots of bubbles. But clay is very black.

L3954B with Burnt Umber and Black Stain

Both replace the 10% zircopax with a black pigment. They darken the engobe to near black. But the stain version (Mason 6600) on the right fires blacker and develops the color of this rutile glaze (Alberta Slip rutile blue) much better. It also produces a perfect glass surface whereas the Umber version on the left develops some pinholing in the inside glaze (GA6A Alberta Slip base).

Black stain L3954F vs. Raw Umber black clay

L3954F black egobe with 7.5% stain

The center bar has 7.5% Mason 6600.
The bottom one has 15%.
The top one is a body havig 10% raw umber.

L3954F black cone 6 engobe fired bars

M340 mugs with L3954F black engobe, Ravenscrag blue