L210

Low temperature, silty smooth, medium plastic, brown-burning, native terra cotta body.

L210 is a low-talc low-fire terra cotta body that Plainsman has made for many years. Its main appeal has been to schools that like its light raw color since this is easier to clean up. L210 burns browner than our other low temperature reds. Because it is low in talc L210 may craze with some commercial glazes (however making your own glaze is easy and much less expensive).

Process Properties

L210 is a mix of one of our low fire red-burning fine grained plastic materials with a silty buff stoneware clay and 10% talc. It has medium plasticity and very slight texture. It is somewhat susceptible to water splitting so we recommend care not to use excessive water in pulling handles and throwing extreme shapes. Where joins with slip are made (i.e. handles), wipe away any excess that gets squeezed out during compression to avoid a split.

We do not recommend L210 for large sculptural ware since it lacks coarser particles and has a fairly high drying shrinkage. To avoid drying cracks use our recommended drying procedures. The most important of these is do what is necessary to make drying even throughout the piece. You can do this using a damp room or covering with a cloth and then plastic to slow down drying (the slow down helps even it out).

Firing

L210 fires to a light brown at cone 04-06. By cone 02 the color dramatically intensifies to a dense stoneware brown. By cone 4 it is over fired.

L210's warm color and strength in the cone 1-3 range make it a good candidate to produce low fire stoneware or vitreous tile. However be careful of warping if shapes are overhung too much.

Like any other low-fire body at cone 06-04, L210 is fairly weak and has high porosity. You might consider bisque firing higher (e.g. cone 03) to strengthen ware if you need to fire at 06-04 for your glaze. Please experiment since the increased density associated with higher bisquing can make it difficult to get the glaze to adhere and dry. Remember that L210 suddenly becomes very dense between 03 and 02 so your bisque firings need to be precise in this range.

Glazing

Please test to determine the best body firing temperature in your situation. Then use a starting glaze recipe for Frit 3124 42.5%, Frit 3134 42.5%, EP Kaolin 15% and test to get the degree of melting needed. If the glaze is too runny, increase the kaolin at the expense of the frit mix, if not melting enough reduce the kaolin. Then stress test in boiling water and ice water to bring out any crazing or shivering and adjust the fit by increasing the amount of Frit 3134 if the glaze shivers or 3124 if it crazes. For example, if it crazes, try 60% frit 3124 and 25% Frit 3134. Another recipe you might try for cone 04 is 85% Frit 3195 and 15% kaolin.

L210 is an ideal candidate for use with cone 2 or 3 stoneware glazes. Keep in mind that transparent glazes may tend to darken the color of the clay more than you expect. For cone 2, increase the kaolin in the glaze to 30%. If the glaze is still melting too much add silica in 5% increments until it is right.

L210 has some coarser particles and thus can pinhole certain glazes. However by soaking the kiln and adjusting the glazes to be more fluid these problems can be solved.

Glaze Recipes

For more information on the already mentioning glaze recipe please visit www.ceramicmaterials.info and search for 'cone 06' in the library area, there is an article on a low fire base glaze. Information is given on how to fit the glaze to your body and how to customize it it for colors, opacity, speck, variegation, etc. For slip decoration, be careful to match drying and fired shrinkage of the slip with the body since low temperatures generate little glass to adhere the slip.

Thermal Expansion

This chart is for the old mix of L210 and was derived from a specimen fired once to cone 04 in the Plainsman lab and tested in an Orton dilatometer (note the quartz inversion hump). We have not tested the new mix yet but it likely has a higher thermal expansion since it contains 10% talc. If you fire to a different temperature, employ different heatup or cooldown rates, or glaze-fire more than once the thermal expansion in your ware may be different than this chart indicates.

Thermal Expansion Chart
Average: 6.4

Physical Properties

 Drying Shrinkage: 6.0-7.0%
 Dry Strength: n/a
 Water Content: 22.0-23.0%
 Drying Factor: C130
 Dry Density: n/a

Sieve Analysis (Tyler mesh):

     +35: 0.0-0.2%
   35-48: 0.5-1.0
   48-65: 0.5-1.0
  65-100: 1.0-3.0
 100-150: 2.0-4.0
 150-200: 5.0-8.0
 200-325: 10.0-13.0

Fired Shrinkage:

 Cone 06: 1.0-2.0%
 Cone 04: 2.0-3.0
 Cone 02: 6.0-7.0
  Cone 2: 7.0-8.0

Fired Absorption:

 Cone 06: 10-12%
 Cone 04: 8.0-10.0%
 Cone 02: 2.0-3.0
  Cone 2: 0.5-1.5

Chemistry

The chemistry has not yet been determined.

News

This body has been stable for many 30 years or more, but in Sept 2003 we made changes in reponse to a material availability problem. Here are the differences (these observations are for batches having a code number whose first four digits are 4555 or greater):

-The firing range is narrower, by cone 02 the body has stoneware qualities and is very strong and dense. This is now the highest recommended firing temperature.

-The fired color is browner. -Drying shrinkage is 6.5-7.0% rather than 6.0-6.5% however drying performance (tendency to resist drying cracks) is similar. -Thermal expansion will be a little higher so glazes should craze less.

Plainsman Clays Ltd.
Box 1266, 702 Wood Street, Medicine Hat, Alberta T1A 7M9
Phone: 403-527-8535 FAX: 403-527-7508

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