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L212

Description

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

L212 bars fired at cone 04, 02, 2, 4 and 6 (bottom to top).

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 underglaze decorated mug fired at cone 03. Outside glaze is G2931H clear. Inside is Crysanthos SG001 white.

If you wish to paint on glazes, many commercial brands are available (there are a wide variety of products from companies such as Duncan, Spectrum, Mayco, AMACO, etc). Most of these are formulated to target the thermal expansion of high-talc bodies (like L213, L212). The high thermal expansion puts the squeeze on the glazes (thereby preventing them from crazing). Many people decorate ware using under-glazes and finish with coats of transparent glaze. Of course, we cannot guarantee that any glaze made by another manufacturer will fit.

Many find that commercial brushing and dipping glazes dry very slowly and drip badly. And they often do not fit well (craze or shiver). And they are expensive. With a little effort you can make your own of both types. And add stain and opacifier powders to make almost any color. There is no need to search for a recipe, we have done it for you. You can mix your own glaze from a pre-mixed powder you buy from us or weigh out your own ingredients. However, at low temperature, there is no one-glaze-that-fits-all bodies. To solve this we have created a three-recipe solution, these have thermal expansions that span the entire range of low fire bodies. And they fire crystal clear (in a drop-and-hold firing). Our Zero3 K transparent glaze fits low talc bodies (like L215) and low fire stoneware (like Zero3), Zero3 H fits high talc bodies (like L213, L212) and Zero3 L fits zero talc bodies (like Terrastone and Buffstone). We recommend cone 04-03 using a drop-and-hold firing schedule (for defect free surface and good transparency). Do not trust electronic controllers to be accurate, we verify using cones and manually program to compensate for error. If you need to fire lower or higher than 03, be sure and do testing first.

Blending the K, H and L glazes is encouraged to get the best fit. We recommend stress testing by boiling-water-into-ice-water (and vice versa) to bring out any crazing or shivering. If crazing occurs, blend in some of the L. If shivering occurs, blend in some of the H. In this way these glazes can be optimally fitted to almost any clay body.

It is also practical to make your own brushing glazes, ones that will work identically to the commercial ones mentioned above. Like the dipping versions, you can blend to tune the thermal expansion to fit your clay body. Click here for more information on how to do this. You will be surprised at how easy it is and how much money you can save.

Buffstone, L212 and L213. Each has its own clear glaze. G2931L, K and H. L is low expansion (for zero talc porous bodies). K is intermediate (for moderate talc bodies like L215 and Zero3 stoneware and porcelain). H is high expansion (for high talc bodies like L212, L213).

Thermal Expansion

We do not supply a thermal expansion value. The reason is that such numbers often mislead users. First, a body has different thermal expansion characteristics when fired at different temperatures, schedules and atmospheres. Dilatometers are only useful when manufacturers can measure bodies and glazes over time and in the same firing conditions. If a chart is supplied here, please view only as a way to compare one body with another.

Another significant issue is that many customers compare measured thermal expansion numbers with calculated values of glazes in efforts to fits those glazes to a body. This does not work. Calculated values are relative only and have limitations that must be understood. The best way to fit glazes to your clay bodies is by testing, evaluation, adjustment and retesting. For example, if a glaze crazes, adjust its recipe to bring the expansion down (using your account at insight-live), fire a glazed piece and thermal stress it (300F into ice-water). If it still crazes, repeat the process.

If we recommend a base clear or glossy glaze, try calculating the expansion of that as a rough guide to know whether your glazes will fit.

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

Safety Data Sheet

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