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A2 Ball Clay

Oxide Analysis Formula
CaO 0.25% 0.02
K2O 0.69% 0.04
MgO 0.43% 0.06
Na2O 0.04% 0.00
TiO2 0.72% 0.05
Al2O3 18.99% 1.00
P2O5 0.03% 0.00
SiO2 65.12% 5.82
Fe2O3 1.84% 0.06
MnO 0.01% 0.00
LOI10.58%
Oxide Weight 473.31
Formula Weight 529.32

Notes

A2 is a ball clay mined in a quarry about 5 km west of Ravenscrag, Sask. It has a very high plasticity and is suitable as an additive to all types of stoneware and earthenware bodies. This material is used in many bodies made by Plainsman Clays.

A2 has some intrinsic iron content which makes it burn cream-white. It also has some physical iron concretion particles which act as a source of specks and iron blossoms in reduction fired clay bodies employing it.

A2 has natural soluble salts that migrate to the surface during drying and leave a brown coloration on the buff-colored fired surface. However with 0.35% barium to solubles are removed. These soluble salts cause gelling during the deflocculation process and thus prevent A2 from being used in slip bodies.

Analysis updated July 97.

388 Ba ppm
34 Sr pmm
23 Y ppm
10 Sc ppm
413 Zr ppm
1 Be ppm
70 V ppm

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 A2 Ball Clay fired test bars

Cone 10 reduction (top), cone 11 down to 8 oxidation below that.

IXL Industries clay quarry near Ravenscrag, Saskatchewan in 1984.

Layers of the Whitemud Formation are being mined. The layer being extracted is a silty stoneware they referred to as the "D member" (equivalent to Plainsman 3D which is mined several miles to the east). Below the D they continued to mine a much whiter kaolinized sand of equal or more thickness. Above the D is a ball clay (equivalent to Plainsman A2). Above that is a light burning stoneware (the combined layers that Plainsman extracts separately as A3 and 3B). A foot-thick layer of much harder volcanic ash is visible in the green over burden at the top. From these stoneware clays they made brick of exceptional quality, firing it as high as cone 10. Twenty years later the company reclaimed this land and today you would be unable to find where the quarry was located.

Mel Noble at Plainsman Clay's Ravenscrag, Saskatchewan quarry

Plainsman 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).

Core sampling at a Plainsman quarry during summer 2021

We are drilling test holes down through about 40 feet of overburden into the seven layers of clay to be mined. The rig assembles five-foot auger-sections, drilling down and pulling out two sections at-a-time. We examine the auger, identify the clays and record the results. At the middle of the auger-full shown you can see the division between the A2 ball clay and the A3 white stoneware, it was about 50 feet down. This hole was 80 feet, that spans tens of millions of years of sedimentation! This is the first time we have been able to sample the entire depth of the overburden, a highly plastic red burning low temperature clay, now we can assess whether it is a useful product.

Links

Materials Plainsman Red Fireclay
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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