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A1 Ball Clay

Description: PR#3 A1, Pyritic bentonitic ball clay

Oxide Analysis Formula
CaO 0.73% 0.07
K2O 0.70% 0.04
MgO 0.88% 0.12
Na2O 0.05% -
TiO2 0.80% 0.06
Al2O3 18.30% 1.00
P2O5 0.40% 0.02
SiO2 59.30% 5.50
Fe2O3 4.07% 0.14
MnO 0.09% 0.01
LOI 13.60%n/a
Oxide Weight 475.55
Formula Weight 550.41


A1 is mined by Plainsman Clays in southern Saskatchewan, Canada. It is at the top of the Whitemud formation just under or perhaps even part of the Battle formation. It is very high in iron stone concretions (pyrite) and soluble iron salts, a heavily stained bentonitic ball clay. While this would be considered a garbage material by most companies, artists and potters do not agree. It is useful in high-temperature reduction brown or dark burning pottery clay bodies to impart plasticity, iron speckle and variations in fired surface character. It usually is not used in amounts above 10%.

Related Information

Ravenscrag Saskatchewan clays fired at cone 10R

Glazeless (top) and with glaze (bottom): A1 (bentonitic), A2 (ball clay), A3 (stoneware), 3B (porcelains), 3C (lignitic ball clay), 3D (silt). The bottom row has also shows soluble salts (SOLU test).

Plainsman A1 ball clay fired test bars

Cone 10 reduction (top), 11 down to 9 oxidation below. The dark color is partly from iron bearing soluble salts that are left on the surface after drying.

Mining the Battle Formation in our quarry at Ravenscrag, Saskatchewan - June 2018

This is the top layer. Battle clay is highly bentonitic, it is the "super hero of plasticity" in the quarry, it is unbelievably sticky. We have considered it "over-burden" in the past, but now will be looking for ways to employ Battle clay in our products and seeking special-purpose markets for it. Only 10% of this can turn a silt into a plastic throwing body! It is also high in fluxes (melts by cone 6). That means we can use it to improve the fired maturity of bodies, reducing the need for talc. Removal of this layer has exposed the top of the White-Mud Formation, the "A1" layer. A1 is employed in high fire bodies to impart brown color and fired speckle.

Mel Noble at Plainsman Clay's Ravenscrag, Saskatchewan quarry

Whitemud formation layers

Plainsman Clays extracts 6 different sedimentary clays from this quarry (Mel knows where the layers separate). The dried test bars on the right show them (top to bottom). The range of properties exhibited is astounding. The top-most layer is the most plastic and has the most iron concretion particles (used in our most speckled reduction bodies). The bottom one is the least plastic and most silty (the base for Ravenscrag Slip). The middle two are complete buff stonewares made by mother nature (e.g. M340 and H550). A2, the second one down, is a ball clay (similar to commercial products like OM#4, Bell). A2 is refractory and the base for Plainsman Fireclay. The second from the bottom fires the whitest and is the most refractory (it is the base for H441G).


Materials Saint Rose Red
Materials Fire-Red
Typecodes Ball Clay
Ball clays are abundant and very plastic and are used in all types of plastic forming bodies. They are not as white-burning or refractory as kaolins but lower in iron and fluxes than bentonites.
By Tony Hansen
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