Highly grogged highly plastic sculpture body.
This body is built on a 50% base of kaolin and ball clay along with 20% of a fine red earthenware with the remainder a high quality grog.
This body is a major departure from traditional Plainsman style native grog bodies. It employs a fine particled, smooth and plastic base clay. This produces a body that is less susceptible to water splitting (while traditional Plainsman sculpture bodies have other advantages, they do split when exposed to water during the sculpting process). Sculpture clay is also more heavily grogged and the grog particles are all coarse (there are no fines like our other sculpting bodies). This smooth-base-with-coarse-grog nature means that particles push down into the clay with less resistance during throwing, making it less abrasive (it is abrasive but not as much as you might expect given the amount of grog it has). Furthermore, while it develops little slip during throwing it still does slip well through your hands and resists twisting (if you work quickly). It is possible to fabricate very overhung and exaggerated shapes.
A note about drying: While the grog proportion is significant and coarse, caution is still needed to make sure that pieces dry evenly (because the clay portion itself is highly plastic).
Sculpture clay fired bars. Cone 10R top. Cone 6 to 11 oxidation (bottom upward).
From a firing point of view, this body is also a significant departure from typical scupture bodies: it fires much more vitreous, thus overhung shapes may warp (although you do have the option of firing to a lower temperature for more fired stability). In addition it employs a low fire red clay to impart fired color (rather than refractory red) to achieve both its tan to brown burning color and maturity.
Without the grog this body base is highly plastic and vitrifies at cone 8. However with the significant grog complement it provides a stable matrix for warp-resistant firing above cone 8. However since it has a vitreous matrix there is need to support pieces well when firing to cone 10. Also be aware that at higher temperatures, smaller increases in firing temperature will produce more than the expected increase in warping. The benefit of the more vitreous nature is that it creates a stronger and more durable fired product that is much less susceptible to freeze-thaw failure.
Be careful not to fire Sculpture clay too quickly, it will fail from steam pressure sooner than our other bodies.
While the body matrix vitrifies at higher temperatures, the grog particles are refractory and porous. Thus the majority of the reported porosity of this body is due to the porosity of the grog.
Since this body employs a low burning red to achieve color it will fire brown rather than red in reduction. Sculpture Clay does not burn with reduction speckle, rather, the lighter color of the grog particles produces a striking buff speckle on a dark background.
Sculpture clay closeup.
Although glazing will not be common, you will find that the more dense matrix of fine clay will produce less glaze defects. At higher temperatures the body fires a darker tan to brown, so light colored glazes will be darkened to some extent.
Drying Shrinkage: 5.0-6.0% Dry Strength: n/a Drying Factor: C110 Water Content: 20.0-21.5% Dry Density: N/A
Sieve Analysis (Tyler mesh):
+48 (300 microns): 20.0-23.0% 48-65 (300-210 microns): 3.0-4.0 65-100 (210-149 microns): 0.05-0.15 100-150 (149-106 microns): 0.05-0.1 150-200 (106-75 microns): 1.0-2.0 200-325 (75-45 microns): 3.5-4.5
Cone 8: 4.5-5.5% Cone 10: 5.0-6.0 Cone10R: 5.0-6.0
Cone 8: 5.0-6.0% Cone 10: 4.0-5.0 Cone 10R: 3.5-4.5
CaO 0.3 K2O 1.3 MgO 0.5 Na2O 0.2 TiO2 1.0 Al2O3 24.2 P2O5 0.1 SiO2 62.4 Fe2O3 2.4 MnO 0.0 LOI 7.6%
It throws well! A cone 10R planter made from Sculpture Clay. By Tony Hansen.
Safety Data SheetClick here for web view (format adheres to Globally Harmonized System of Classification and Labelling of Chemicals - GHS)