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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.
L213 is not made from white burning ball clay and talc as are typical ceramic slips. Thus it does not burn nearly as white.
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.
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 ducation/creating_a_non-glaze_ceramic_slip_or_engobe_97.html.
Drying Shrinkage: 6.0-7.0% Dry Strength: n/a Water Content: 21.5-23.0% Drying Factor: C120 Dry Density: 1.96
+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
CaO 0.5 K2O 1.3 KNaO 0.0 MgO 10.2 Na2O 0.1 TiO2 0.5 Al2O3 14.2 P2O5 0.0 SiO2 64.4 Fe2O3 1.2 FeO 0.0 MnO 0.0 LOI 7.6%
|Plainsman Clays Ltd.
702 Wood Street, Medicine Hat, Alberta T1A 1E9
Phone: 403-527-8535 FAX: 403-527-7508