L215

Low temperature, slightly sandy, medium plastic, red-burning, native, talc 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 15% talc in its recipe. Although it is more difficult to produce ware of light colors with a red body, many people find that opacified white glazes can be used effectively on red burning materials. 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 bodies.

Process Properties

L215 is a mix of our low fire native Redearth and middle fire Redstone materials with an additional 15% fine red-burning sand. It thus has medium plasticity and a slight texture or tooth. It has better drying properties than our other terra cotta mixes for small items. Its relatively low drying shrinkage and grainy surface means that it will hold slip or terra-sig decoration. However, we do not recommend L215 for large sculptural ware since it lacks the dry strength, plasticity, and coarser particles necessary.

Firing

Cone 04

Cone 02

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 so that small changes in chemistry, mineralogy and particle size can mean that at temperatures above cone 2 it may hold together one time while on another occasion it may bloat and warp badly. 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 only slight 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).

Because of the fine sand it contains, the fired surface of L215 displays a slight grainy texture compared to the relatively smooth surface of our Majolica body.

Since terra cotta bodies are weak and porous at cone 06-04 bisque fire as high as possible (cone 03 is a good compromise, it is much stronger and the matrix will still absorb enough water during glazing).

Glazing

Since L215 has added talc to increase its thermal expansion it is suited for use with commercial pre-mixed glazes to produce a craze free surface. However, keep in mind that this body is not guaranteed to work with any pre-mixed glaze. We still recommend an ice-water:boiling water test to prove that clay and glaze will work together.

If you are mixing your own glazes and they are shivering or crazing on this body, you might try one of our other low fire reds such as Majolica. L215 responds well to our recommended low fire base glaze recipes.

Since L215 is not ground to our finest size, there is some danger of pinholing if the glaze is not given adequate time to even out at top temperature. We thus recommend at least some soaking time during all firings. Also keep in mind that transparent glazes will tend to darken the color of the clay somewhat.

Glaze Recipes

You can develop a compatible glossy or matte base for this body from our suggested starting point base recipes available on our Internet web site at http://digitalfire.com/education/glaze/cone06.htm. 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.

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: 10.0-12.0%
 Cone 02: 3.5-5.0
  Cone 2: 1.0-2.0

Chemical Analysis

 BaO       0.0
 CaO       0.5
 K2O       2.8
 MgO       4.3
 Na2O      0.1
 TiO2      0.6
 Al2O3    13.2
 P2O5      0.3
 SiO2     67.9
 Cr2O3     0.0
 Fe2O3     5.1
 MnO       0.0
 LOI       5.2%

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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