H440 body development

H440

H440

Notes

*This is our traditional H440 plastic clay body, it has been used for throwing and handbuilding and has been made since the 1970s.

It has a unique iron red fired color that epitomizes what can be made by mixing 42 mesh powders of the native materials that we mine in Manitoba and Saskatchewan.

It has a few problems that, if solved, would make it much more useful.
-The degree of maturity is not suitable for functional ware (often it is over 5% porosity). Recent testing has shown that added feldspar can reduce that figure without loss of surface character (provided enough iron is present).
-The texture: It is too sandy and gritty.
-The plasticity: It is not plastic enough to pull up large forms or make thinner functional pieces.
-Water splitting: The lower plasticity makes the body susceptible to this issue.
-Color: We believe that a richer red is possible, one that would become metallic in heavily reducing firings.

Pictures

P7088 H440 fired bars

Cone 10R top
Cone 10 down to 7 oxidation (moving downward).
Fired color is darker than normal in reduction.

P5884 H440 fired bars

Cone 10R top
Cone 10 down to 8 (moving downward).

P7088 H440 sculpture by Grace Warren

About 3 feet tall
Done by casting a plaster shell around a model and then pressing clay into that shell.
Fired color darker than normal.

P7088 H440 27kg vase

Made by Kat Valenzuela
The fired color is darker than normal.

New H440 Functional Proposal #8

Total:5,246,358.00 (R)

Notes

*This is the product of many previous tests to find a blend of our Saint Rose Red iron-stained fireclay and our A2 ball clay that fires to a rich red color but also has good plasticity. St. Rose has very poor workability, it turns out that a lot of ball clay is needed to plasticize it. Fortunately that ball clay also makes for a smooth and pleasant to use material.

Unfortunately, because these two materials are refractory, no combination of them fires to anything close to the degree of vitrification we want. This turned out to be a blessing in disguise because of the need for a feldspar addition. This feldspar can be fine-tuned to create the exact degree of maturity needed to achieve a balance of iron stoneware surface character and a sufficient degree of vitrification for making functional ware. Using our SHAB test we can detect a feldspar change of as little as 1%! We already know from previous tests that 12% iron is too much.

The higher than 7% drying shrinkage indicates this is indeed a plastic body. It will be suitable to throw much larger forms than the old mix. Combining this with its deeper color will mean that it can support significant grog additions without impact on the fired character.


The throwing properties of this are very good, it only feels sandy if used when stiff - at normal stiffness it is smooth.

We are anticipating being able to maintain a high degree of control of the degree of vitrification (because of the feldspar addition), creating a unique and high value product.

Pictures

L4168G6, G7, G8

Left: L4168G6 - 2.8% 12% Cus
Middle: L4168G7 - 3.5% 12.8 Cus
Right: L4168G8 - 1.4% 12.7 NS

G6 is 48:40:12 StRR:A2:Custer
G7 is 37:50:12 StRR:A2:Custer
G8 is 37:50:12 StRR:A2:NS

L4168G2 to G5 Cone 10R bars

These demonstrate varying proportions of St. Rose and A2 along with adjustments to the percentage of feldspar to study the impact on surface character and color. The G5 achieved the surface we want (but it used Custer Feldspar which is no longer available and was still a little short on plasticity). The G9 mix resolves both issues.

G4168G5 mugs with Ravenscrag, G2571 glazes

These mugs were fired at cone 10R. The body is L4168G5 (50% Saint Rose Red, 40% A2, 10% Custer feldspar). The heavy iron specking is being sourced by both of these very unique clays. The left glaze is GR10-CW Ravenscrag Talc matte with added Zircopax. The right one has that same glaze on the inside and G2571A bamboo matte on the outside.
The G9 recipe ended up adding more A2 (thus less St Rose) and using Nepheline instead of Custer.

Proposed H440 Casting Body #5

Total:100.25

Notes

*This is the product of many previous tests to try to create a casting body that fires to a similar surface as Plainsman H440. Formerly we used Redart to supply the needed iron. It also served as a source of fluxes to impart fired maturity (the other recipe ingredients were mostly refractory). However all mixed just produced ugly brown shades (with no variegation). This is the first to use IMCO C-Red, it is a refractory red burning clay. It is very high in iron and has very good slip casting properties. It does not gel the slurry the way iron oxide does.

We are using the L2596G H550 casting recipe as a starting point and substituting the C-Red for the ball clay (and cutting nepheline since this needs to be less vitreous to produce the desire surface character).

We are leaving out the Ilmenite on initial testing, it settles in the slurry. Later we will make a separate slurry and do a pour in pour out to precede the the other recipe. That will mean that only the exterior surface of pieces with fire with speckle.

Pictures

L4023F and L2596G at cone 10 oxidation

L2596G, L4023F mugs fired to cone 10 oxidation

Spectrum 1235 outside, Spectrum 1200 inside.