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L215

Description

Low temperature, smooth, plastic, red-burning, native, talc-containing terra cotta body. L215 is intended for use with the commercial glazes available from Duncan, Mayco, Spectrum, and similar companies. It achieves fit to these glazes with the use of only 10% talc in the recipe. L215 is made from natural red-firing terra cotta clays that melt at low temperatures, thus it develops better fired strength than more refractory white burning low fire bodies.

Process Properties

L215 is a mix of our M2 native clay, talc and ball clay. Plasticity, and therefore throwing performance, are excellent.

Firing

L215 Fired Bars (cone 4, 2, 02, 04, 06 top to bottom)

This material fires to a light red at cone 04-06 and the color intensifies to a brick red by cone 02. Further temperature increase shifts toward deep red, then brown, until it reaches its maximum strength and dark brown color around cone 1. The body becomes volatile above this range. Furthermore, like many terra cotta bodies, the color evolution is much more rapid from cone 02-1. Thus, ware fired in this range without good firing control will be subject to wide variations in color with comparatively small changes in firing temperature. Also, although the fired body may appear stable against warping at cone 03-02, do not overestimate its ability to withstand warping on extremely overhung shapes (e.g. bowls with flared flat rims).

Terra cotta bodies are weak and porous at cone 06. It is better to fire to cone 04-03, almost any low fire glaze will work fine there also.

Glazing

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.

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: 5.0-6.0%
 Dry Strength: n/a
 Water Content: 19-20.5%
 Drying Factor: C110-C120
 Dry Density: 1.98

Sieve Analysis (Tyler mesh):

     +48: 0.5-1.0%
   48-65: 2.0-5.0
  65-100: 5.0-9.0
 100-150: 4.0-7.0
 150-200: 3.5-6.0
 200-325: 8.0-12.0

Fired Shrinkage:

 Cone 04: 1.5-2.5%
 Cone 02: 4.5-5.5
  Cone 2: 6.0-7.5

Fired Absorption:

 Cone 04: 8.0-10.0%
 Cone 02: 3.5-5.5
  Cone 2: 1.0-2.0

Gallery

L215 with underglaze decoration and G2931K clear glaze. Fired at cone 03 in 3 hours cold-to-cold.

Buffstone and L215 with underglaze decoration and G2931 clear glazes. But they are not the same. The G2931L glaze (left) has a lower thermal expansion (to prevent crazing on Buffstone). The G2931K glaze fits L215 because the latter contains some talc (which raises its expansion). Both of these mugs have survived a 300F-to-ice-water thermal shock without crazing or shivering. If you switch the glazes the Buffstone mug would craze it and the L215 would shiver it off in flakes.

Safety Data Sheet

Click here for web view.

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