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A3 Stoneware Clay

Description: Pr#3 A3, Buff Firing Stoneware Clay

Oxide Analysis Formula
CaO 0.25% 0.02
K2O 2.00% 0.11
MgO 0.65% 0.09
Na2O 0.05% -
TiO2 0.65% 0.04
Al2O3 19.25% 1.00
P2O5 0.02% -
SiO2 66.00% 5.82
Fe2O3 1.50% 0.05
MnO 0.01% -
LOI 8.40%n/a
Oxide Weight 478.90
Formula Weight 522.81


A high temperature plastic clean buff stoneware mined at Ravenscrag, Sask. Many of their low, middle and high temperature buff burning clay bodies are based on this material. It is balanced and almost usuable as a cone 10 stoneware straight out of the ground.

Analysis was done July 97.

357 Ba ppm
33 Sr pmm
24 Y ppm
14 Sc ppm
261 Zr ppm
2 Be ppm
82 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 A3 Native Stoneware fired test bars

These are fired to cone 6, 8, 9 and 10 (top to bottom).

Physical properties for Plainsman A3

This chart shows lab measurements and calculated results for drying shrinkage, fired shrinkage, absorption, drying factor, sieve analysdis, LOI and water content of plastic material.

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).

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.


Materials B Clay
Typecodes Clay Other
Clays that are not kaolins, ball clays or bentonites. For example, stoneware clays are mixtures of all of the above plus quartz, feldspar, mica and other minerals. There are also many clays that have high plasticity like bentonite but are much different mineralogically.
Plainsman Material Safety Data Sheets (MSDS)
By Tony Hansen
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