Sandy brown stoneware. This is a mixture of two light-duty fireclays (20% IMCO M-4, 20% IMCO 400), OM#4 ball clay (20%), IMCO Burgundy low fire red burning clay (20%), 15% silica sand and 4% Mulcoa 47-35 grog.
In 2016 the red clay/flux portion of the recipe, "Banta Red", was no longer available. The supplier, IMCO, recommended their Burgundy clay as a substitute, we tested that and began using it instead. It was not as strong a flux, so some density was compromised, increasing the body porosity. But it was not enough to be an issue. But F95 has become even less vitreous (meaning further loss of maturity in one-or-more of the IMCO 400, IMCO M-4 and/or Burgundy ingredients). We have found a solution that greatly improves the density of current runs: An 85:15 mix of F95 and L210 moves porosity down to about 4%. You can even adjust the proportion to suit (e.g. a 75:25 mix will deliver 2.7% porosity at cone 6 but the color will darken somewhat). This blend actually improves body workability also, making it more plastic.
The test bars are F95 and cone 6 and 7. The cup is an 85:15 mix of F95 and L210. The L210 significantly matures the body, restoring it to historical density sufficient to resist seepage of water while maintaining the color.
F95 is light-green-colored in the wet state. The 60% fire clay/ball clay content means that is easy-to-throw, even when quite soft. Although it contains grog and sand, it feels smooth to throw without generating excessive slip during throwing (of course it is somewhat abrasive against the wheelhead).
The leather-color of F95 at cone 6 depends on it NOT being vitreous (if fired to oxidation maturity, beyond cone 8, surface aethetic is lost as it turns solid greenish). Fired porosity at cone 6 is intended at 5% (a typical stoneware is half of that).
Because this body contains significant percentage of silica sand it is subject to cracking if ware is fired up or down through quartz inversion temperature too fast. The grog and silica sand also increase the fired porosity. The sand and grog are needed to cut the drying shrinkage in this otherwise very plastic blend of clays.
The centre bar, and one below it, are fired to cone 5 and 6, they are burning the intended light sandy tan. By cone 8, the top bar, the color is lost as vitrification begins (these bars were made in 2010 when Banta was still available).
Because F95 does not fire vitreous at cone 6, glazes must fit (not craze) to avoid seepage of water. If you need help to deal with a crazing issue please contact us. To guarantee the clay will not seep please use a higher percentage of L210 (as noted above).
To mix this body yourself you could simply use 60% ball clay and 20% Redart as a starting point (with sand and grog). Redart, a low fire and consistent red-burning body, is available everywhere. IMCO 400 and M-4 are similar to Lincoln Fireclay, if you can get that then use 40% Lincoln and 20% ball clay). Experiment with different proportions of Redart to achieve the compromise of color and maturity desired (remembering that you will have to settle for non-vitreous to achieve this type of color).
We do not supply a thermal expansion value. The reason is that such numbers often mislead users. First, a body has different thermal expansion characteristics when fired at different temperatures, schedules and atmospheres. Dilatometers are only useful when manufacturers can measure bodies and glazes over time and in the same firing conditions. If a chart is supplied here, please view only as a way to compare one body with another.
Another significant issue is that many customers compare measured thermal expansion numbers with calculated values of glazes in efforts to fits those glazes to a body. This does not work. Calculated values are relative only and have limitations that must be understood. The best way to fit glazes to your clay bodies is by testing, evaluation, adjustment and retesting. For example, if a glaze crazes, adjust its recipe to bring the expansion down (using your account at insight-live), fire a glazed piece and thermal stress it (using an IWCT test, 300F into ice-water). If it still crazes, repeat the process.
If we recommend a base clear or glossy glaze, try calculating the expansion of that as a rough guide to know whether your glazes will fit.
Drying Shrinkage: 5.5-6.5% Drying Factor: C120
Target Fired Shrinkage:
Target Fired Absorption:
Cone 4: 5.5-7.0% Cone 6: 4.0-5.0 Cone 8: 2.5-3.5
Safety Data SheetClick here for web view.
|Plainsman Clays Ltd.|
702 Wood Street, Medicine Hat, Alberta T1A 1E9
Phone: 403-527-8535 FAX:403-527-7508