Low temperature, smooth, medium plastic, light cream to grey buff burning, refined talc earthenware. L212 is a mix of our cleanest native stoneware clays with 33% added talc. It is intended for good fit with commercial bottled glazes (i.e. Duncan, Mayco, Spectrum) and is a popular body for use in schools.
We have added a little ball clay and bentonite to improve and control the plasticity of L212 while it still retains the unique working properties and dry strength common to bodies in its family (H550, M340, Buffstone). Like classic ball clay:talc ceramic mixtures, this body has a unique and very pleasant smooth feel for throwing and modelling forms of all shapes and sizes.
L212 dries fairly quickly with minimal cracking. However it is fine grained so joins should be made using low water content slip and applying as much pressure and lateral movement as possible.
Although this body does not burn as white as L213 it is less expensive for us to manufacture. It fires best at cone 06-04. The color darkens to a yellow buff by cone 2, then to a grey buff by cone 4 and above. If you want to produce denser stronger ware you might consider firing L212 to cone 02 or higher. However we recommend you do this with caution because bodies of this type tend to melt suddenly. Although L212 might appear OK at cone 4, ware tends to be brittle at this temperature. Also, the volatility is not consistent; that is, L213 will melt at different temperatures for different runs.
Since L212 contains a significant amount of talc, it has a unique firing behavior. The talc significantly increases the thermal expansion of the ware. This is a disadvantage if ware will be used for functional purposes since it will not have as good thermal shock resistance. However the advantage is that contraction during cooling squeezes the glaze onto the ware and helps prevents it from crazing.
It is important to realize that talc bodies of this type do not vitrify at cone 06-04. A typical thinly cast or thrown shape can often be torn apart with your bare hands.
Since L212 contains bentonite you must be careful not to fire too fast during early stages. Ball clay is very plastic and fine and thus does not vent water vapor quickly during the water smoking period of firing. We recommend that you candle the kiln overnight to give the ware a chance to dry thoroughly before starting the firing the next morning.
Although cannot guarantee that commercial glazes will not craze or shiver we do test multiple types for fit. Regarding toxicity: Do not assume food safety of brightly colored glazes in your kiln without a leach test (e.g. GLLE test). Consider using a transparent or white liner glaze for food surfaces.
Although commercial bottled products are expensive, they are convenient. It is practical to make your own dipping or brushing base glazes that dry faster and fit better (do not craze or shiver). Adding powdered stains is also possible. There is lots of documentation on how to make and mix our G1916Q and G3879 and recipes. Each of them has variations to enable tuning fit any body. It is possible to mix them as a brushing glaze, base coat or dipping glaze.
For slip decoration and engobes be careful to match the fired shrinkage of the slip with the body. Where we do not recommend a specific engobe recipe use a one based on the porcelain itself. Add 2% VeeGum or Bentonite (the extra stickiness helps it adhere well to leather hard ware). Be careful about adding fluxes (e.g. frit), this increases fired shrinkage (the mismatch with body can cause flaking) and can compromise opacity.
Buffstone, L212 and L213. Each has its own clear glaze. G2931L, G2931K and G2931H.
We do not supply thermal expansion values. If a chart is supplied here, please view it only as a way to compare one body with another. Please note that, although you may calculate the thermal expansion of a glaze, this cannot be done for clay bodies since they do not melt. The best way to fit glazes to clay bodies is by testing, evaluation, adjustment and retesting. For example, if a glaze crazes, adjust its recipe to bring the expansion down, fire a glazed piece and thermal stress it (using an IWCT test, 300F into ice-water). If it still crazes, repeat the process.
Drying Shrinkage: 6.0-7.0% Dry Strength: n/a Water Content: 21.5-23.0% Drying Factor: C120 Dry Density: 1.96
Sieve Analysis (Tyler mesh):
+65: 0.1-0.5% 65-100: 0.5-1.5 100-150: 1.0-2.0 150-200: 1.0-2.0 200-325: 6.0-10.0
Cone 04: 1.5-2.5% Cone 02: 3.0-4.0 Cone 2: 4.0-5.0
Cone 04: 11.0-14.0% Cone 02: 9.0-12.0 Cone 2: 5.0-7.0
Safety Data SheetClick here for web view.
|Plainsman Clays Ltd.|
702 Wood Street, Medicine Hat, Alberta T1A 1E9
Phone: 403-527-8535 FAX:403-527-7508