A3 Stoneware


High temperature, smooth, medium plastic, vitreous, buff-white firing, clean native stoneware. A3 clay is not a blend of materials, it is mined from our Ravenscrag, Sask. quarry from a single clay seam. It provides the basis for most of our high-fire stoneware bodies. Its plasticity is slight greater than a standard clays. It can be used as-is for the production of cone 8-9 stoneware pottery. The seam of raw clay is grey in color.

Process Properties

A3 clay is very smooth and slick and its plasticity is a little higher than other clays. This material is fine enough that a simple slaking process on the dry lumps will create a slurry of which +90% passes a 325 mesh screen. From a workability point of view A3 clay is suitable as a major ingredient in stoneware clay bodies. It is balanced enough that it can actually be the only ingredient in a cone 10 buffstone storeware.

Although A3 clay is very fine, it does not disperse or deflocculate. Soluble materials within the clay impede the action of normal deflocculants resulting in gelling of the slurry.


Fired test bars of A3. Cone 10R top. Cone 7 to 10 oxidation (bottom upward).

Since A3 clay is naturally vitreous (but not overly so) at cone 10 it is not necessary to add feldspar to flux it. Midstone can be added to improve vitrification.


A3 stoneware is high in quartz and not difficult to fit glazes to, especially at higher temperatures. Its very fine grain and minimal impurities mean that it will present few problems with regard to glaze pinholing.

Physical Properties

 Drying Shrinkage: 1995 6.3-7.3%, 1999 6.0-7.0
 Dry Strength: n/a
 Water Content: 22.0-23.0
 Drying Factor: C130
 Dry Density: n/a

Sieve Analysis (Tyler mesh):

     +48     (300 microns): 0-0.1%
   48-65 (300-210 microns): 0.0-0.3
  65-100 (210-149 microns): 0.2-0.8
 100-150 (149-106 microns): 1.0-2.0
 150-200  (106-75 microns): 1.0-3.0
 200-325   (75-45 microns): 3.0-8.0

Fired Shrinkage:

             1995      1999
   Cone 6: 5.0-6.0%  4.0-5.0%
   Cone 8: 5.5-6.5   4.5-5.5
  Cone 10: 6.0-7.0   5.5-6.0
 Cone 10R: 6.0-7.0   6.0-7.0

Fired Absorption:

             1995      1999
   Cone 6: 1.0-2.0%  4.0-5.0%
   Cone 8: 0.5-1.5   2.5-3.5
  Cone 10: 0.2-0.8   1.5-2.5
 Cone 10R: 0.5-1.5   1.0-2.0

Chemical Analysis

 BaO       0.4
 CaO       0.2
 K2O       2.0
 MgO       0.7
 Na2O      0.1
 TiO2      0.6
 Al2O3    19.4
 P2O5      0.0
 SiO2     66.5
 Fe2O3     1.5
 MnO       0.0
 LOI       8.4%

Safety Data Sheet

Click here for web view (format adheres to Globally Harmonized System of Classification and Labelling of Chemicals - GHS)

Logo Plainsman Clays Ltd.
702 Wood Street, Medicine Hat, Alberta T1A 1E9
Phone: 403-527-8535 FAX:403-527-7508
Email: plainsman@telus.net