Terrastone

Description

Our entry-level low temperature native terra cotta. Terrastone is a hi-brid body, a mix of native and refined materials. M2 is the native material, it is a clean iron-bearing native clay. 20% refined ball clay and a small amount of bentonite are added for plasticity and 10% pyrophyllite to reduce thermal expansion. Terrastone burns to the classic terra cotta color (a little lighter than L215) and is naturally soluble-salt free. Most often used in schools, it is a good choice for beginners at low-firing temperatures. Just make your ware, trim and decorate it at leather hard stage, dry it, bisque fire it and then dip ware in the clear glaze (see below) and fire to cone 03 (for optimal results, see below for detail).

News

Jan 2017: The recipe of this body in new and improved. This data sheet explains the details. If, for any reason, you prefer the old Terrastone, please use L215 (all of its physical properties, including color, shrinkage, absorption and sieve analysis, are the same as the old Terrasstone).

Process Properties

Terrastone is pleasant to work with and plastic. It is easy to dry compared to porcelains, but there is still need for caution. Focus on drying ware evenly, do not let one part of a piece get ahead of any other part during any stage of drying. Ware can be dried quickly if is done so evenly. Unevenly dried ware will often crack even if dried very slowly.

Firing

Terrastone fires to a light red at cone 04-06. As temperature is gradually increased, the red color intensifies to a brick red at cone 02. Further increase shifts toward brown. It's maximum practical reliable firing temperature is cone 02. While many people fire to cone 06, we recommend cone 04 or even better, cone 03 (strength and durability are far better at cone 03 than cone 04). Almost any low fire commercial glaze or underglaze can easily withstand cone 03, infact they are better at 03.

Terrstone fired bars from cone 06 (bottom) to cone 4 (top).

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).

Terrastone mug fired at cone 03 with a Zero3 glaze. It was decorated with unglazes at leather hard, then dipped in the clear after bisque. It was fired cold-to-cold in less than four hours.

Being a terra cotta, the more porous nature affords Terrastone better thermal shock resistance and ability to fire faster than stoneware bodies. In fact, Terrastone is quite suitable for entry-level production of functional pieces at cone 03 provided ware is completely glazed (having minimal unglazed surface) and can survive thermal shock stressing of 300F-to-icewater without crazing.

Physical Properties

 Drying Shrinkage: 6.0-7.0%
 Dry Strength: n/a
 Water Content: 21.5-22.5%

Sieve Analysis (Tyler mesh):

     +65: 1.0-2.0%
  65-100: 2.5-3.5
 100-150: 2.0-3.0

Fired Shrinkage:

 Cone 04: 1.5-2.5%
 Cone 03: 3.5-4.5
 Cone 02: 4.0-5.0

Fired Absorption:

 Cone 04: 9.0-11.0%
 Cone 03: 6.0-7.5
 Cone 02: 4.5-6.0

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