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L213

Description

Low temperature, smooth, medium plastic, off white to white burning, refined high-talc earthenware for modelling or casting. L213 is available in a pugged plastic version and as a casting slip. Both are a 50:50 mix of AmTal Talc and KT#1-4 Ball Clay. Each has a 2.5% addition of calcium carbonate. This recipe is a standard that has been used in hobby ceramics across North America for many decades. The casting version of L213 adds 0.5% bentonite and the throwing one 3.5% bentonite. It is both plastic for modelling yet easy to work with as a casting body. L213 is the best choice for people who intend to use commercial premixed glazes from companies like Duncan, Mayco, Spectrum, etc. and who need a white burning material.

Process Properties

L213 thrown surface texture.

L213 is very slick and smooth and throws and models well for forms of all shapes and sizes. Few bodies of any type can match the plasticity and drying performance of a ball clay:talc mix. Many of our customers sculpt large forms using L213.

You can make forms that combine plastic L213 elements from formed and mold-made elements. If you are working with the casting slip also consider using the deflocculated slurry to join sections since its much lower water content produces less shrinkage. However do not expect the same drying performance from L213; slip cast ware typically has much thinner and more uniform wall thicknesses than hand formed ware.

Firing

L213 fired bars. Cone 04, 02, 2, 4 and 6 oxidation (bottom to top).

L213 burns very white from cone 06 to cone 2 due to the lack of a glassy phase that darkens iron and the use of special whiter burning ball clay and talc. As a result you can apply a transparent glaze (for cone 06-04) and achieve clean looking ware and colored glazes fire to much brighter shades.

Above cone 2 the fired body color shifts to grey-buff. Still, L213 can be fired much higher without bloating or melting (we have gone all the way to cone 10R), however please experiment in your circumstances to determine how high you can practically fire it.

The large amount of talc in L213 increases the thermal expansion of ware fired at cone 04-06 (as you can see on the graph). Care is required if ware will be used for functional purposes requiring thermal shock resistance.

Since L213 is 50% ball clay (which tends to block venting of water vapor) you must be careful not to fire too fast during early stages. We recommend preheating the kiln overnight to give the ware lots of chance to dry thoroughly.

Glazing

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.

Casting Recipe

If you want to start casting it is very important to understand the deflocculation process and how to measure viscosity and specific gravity to maintain the slurry. There is a page on the Internet at here that deals with this.

In our lab we use the following recipe for testing (scale this up to the batch size that you need):

L213C dry   1500 g
Water        700 g
Darvan #7   8-10 g

Start with the minimum amount of Darvan and mix well.
This recipe should yield a conservative specific gravity of 1.74. We do not suggest adding any more water if it is not fluid enough. Instead add more Darvan to the maximum recommended.

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.

Thermal Expansion Chart. Average: 7.9.

Physical Properties

 Drying Shrinkage: 6.0-7.0%
 Dry Strength: n/a
 Water Content: 21-22%
 Drying Factor: A000
 LOI: 11-12%
 Dry Density: n/a

Sieve Analysis (Tyler mesh):

  65-100: 0.1-0.2%
 100-150: 0.1-0.4
 150-200: 1.0-2.0

Fired Shrinkage:

  Cone 06: 1-2%
  Cone 04: 2-3%
  Cone 02: 2.5-3.5
   Cone 2: 2.5-3.5

Fired Absorption:

  Cone 06: 13-15%
  Cone 04: 11-13
  Cone 02: 9-11
   Cone 2: 8-10
   Cone 4: 9-11
   Cone 6: 10-13

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