L215

Description

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

L215 with underglaze decoration and G2931K clear glaze. Fired at cone 03.

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

If you wish to paint on glazes, many commercial brands are available. Use these in conjunction with under-glazes to create many effects. To get the best defect-free surface, use a drop-and-soak firing schedule (see link below). Unfortunately these may or may not fit.

If you wish to dip your ware to glaze it then commercial glazes may not be practical (they often dry very slowly and drip badly). The answer is a recipe. Mixing your own glaze from a pre-mixed powder you buy from us (or weighing out your own ingredients) is more economical. However at low temperature it is very difficult provide one-glaze-that-fits-for-everyone. But if circumstances are narrowed, it is practical. For example, we have found that for making functional ware the G2931K Zero3 transparent glaze fits this body well at cone 03. That cone number is important. We do not trust electronic controllers to be accurate, we verify using cones and manually program to compensate for error (we recommend you do the same). If you need to fire lower or higher than 03 you might experience crazing. The G2931B glaze is a variant of the above, it has a lower thermal expansion but is not as glossy and ultra-clear (technical info is available here). By blending some of that into the G2931K you will be able to develop a glaze that fits for you. Another option is the G1916M recipe, it is highly expansion adjustable.

We recommend stress testing by boiling-water-into-ice-water (and vice versa) to bring out any crazing or shivering in your functional ware. If that happens, make changes and retest.

To get the best defect-free surface please consider using a drop-and-soak firing schedule (you can find more information about it on this page).

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

Safety Data Sheet

Click here for web view (format adheres to Globally Harmonized System of Classification and Labelling of Chemicals - GHS)

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