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Low to medium fire, smooth, medium plastic, buff burning, native material blend for earthenware or medium temperature
Buffstone is a simple mix of two of our smooth fine stoneware clays with 10% added fine sand. Like Terrastone, this body contains
no barium carbonate. Buffstone is pleasant to work with and is suitable for the production of functional and decorative ware in
low and medium temperature electric oxidation firing. If you are using this material in an educational setting, please check our
web site for an article on making the children's first experience with clay a memorable one. We also have a number of videos
available on clay basics.
Buffstone has medium plasticity and feels slick yet has good drying properties. However if ware is being modelled or handbuilt
extra drying precautions are appropriate if pieces are of uneven thickness. To avoid cracking use slip of low water content to
join, apply as much pressure and lateral movement as possible, and cover ware with a cloth and plastic to slow it down and even
out the drying. You might consider preparing a batch of slip and storing in lidded plastic containers (you can add a little grog
to it for even better joining).
Because it does not contain barium carbonate, Buffstone has one property that you must be aware of. The natural soluble salts in
the clay come to the surface during drying and are left in a layer whose distribution across the surface is determined by the
nature of the drying. After firing this surface film appears as a whitish scum in a manner similar to the efflorescing that occurs
on red terra cotta brick walls. However, this behavior is not normally an issue if the ware is being glazed.
While it works well as a middle temperature stoneware (to cone 8), Buffstone has been sold primarily as a non-firing and low fire
clay to the school markets. Like L211, Buffstone is not volatile and thus restricted to use at low temperatures. It gradually
matures and vitrifies over a wide range from cone 2 to about cone 8. When fired at cone 04-02, it is a yellow buff color and is
porous like any other earthenware body.
Buffstone does not contain talc as most other buff earthenwares and thus it does not exhibit the higher overall expansions
associated with talc bodies. This makes it more suitable for ware which will be exposed to sudden temperature changes but also
makes it harder to match glazes without crazing.
Most people use commercial glazes. You may have to try different brands to find one that fires craze-free in your circumstances.
However in many educational settings, crazing will not matter.
If you are glazing, we recommend that Buffstone be used for ware which is glazed entirely in order to avoid the appearance of the
white solubles film on bare surfaces. If you are not using this body in a school setting, you might consider using L212 or L213.
Try a starting glaze recipe of Frit 3124 42.5%, Frit 3134 42.5%, EP Kaolin 15% and test to get the degree of melting needed. If
the glaze melts too much, add 5% silica or increase the kaolin. If it is not melting enough reduce the kaolin. Stress test in
boiling water and then ice water to bring out any crazing or shivering. Adjust the fit by increasing the amount of Frit 3134 if
the glaze shivers or 3124 if it crazes. Once your transparent is working you can use it as a base to create other glazes by adding
colorants, opacifiers, variegators and specking agents. You can find more detail at http://digitalfire.com/4sight/education/g1916
For slip decoration, be careful to match drying and fired shrinkage of the slip with the body and tune the amount of frit to get
good adherence with the body. You can find more information at http://digitalfire.com/4sight/e
The chart shown was produced from a specimen fired once to cone 04 in the Plainsman lab and tested in an Orton dilatometer. If you
fire to a different temperature, employ different heatup or cooldown rates, or glaze-fire more than once the thermal expansion in
your ware may be different than this chart indicates.
Drying Shrinkage: 5.5-6.5%
Dry Strength: n/a
Water Content: 19.5-20.5%
Drying Factor: C120
Dry Density: n/a
Sieve Analysis (Tyler mesh):
Cone 04: 0.5-1.5%
Cone 02: 2.0-3.0
Cone 2: 3.0-4.0
Cone 4: 4.0-5.0
Cone 6: 5.0-6.0
Cone 04: 11.0-14.0%
Cone 02: 9.0-11.0
Cone 2: 8.0-10.0
Cone 4: 5.5-7.5
Cone 6: 2.0-3.0
||Plainsman Clays Ltd.
702 Wood Street, Medicine Hat, Alberta T1A 1E9
Phone: 403-527-8535 FAX: