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L212

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.

Process Properties

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.

Firing


Cone 04

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.

Glazing

L212 is a good choice if you wish to use commercial pre-mixed glazes (L213 fires whiter but it is more expensive). L212 is very fine and thus has the little likelihood of producing pinholing in glazes (soak the firing at top temperature if it does). You will find there is an amazing variety of products from companies such as Duncan, Spectrum, and Mayco.

Glaze Recipes

To mix your own glazes 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 m_cone_06-04_base_glaze_226.html.

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.

Physical Properties

 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

Fired Shrinkage:

 Cone 04: 1.5-2.5%
 Cone 02: 3.0-4.0
  Cone 2: 4.0-5.0

Fired Absorption:

 Cone 04: 11.0-14.0%
 Cone 02: 9.0-12.0
  Cone 2: 5.0-7.0

Chemical Analysis

 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%

News

We sometimes experience difficulties pugging L212. This is a problem common to talc-clay blends. You may notice a slight marbling effect in the slug at times but this disappears after wedging.
Logo Plainsman Clays Ltd.
702 Wood Street, Medicine Hat, Alberta T1A 1E9
Phone: 403-527-8535 FAX: 403-527-7508
Email: plainsman@telus.net
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