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).
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).
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.
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).
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 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.
You can blend the K, H and L glazes 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. You will be surprised at how easy it is and how much money you can save.
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.
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 (using an IWCT test, 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.
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
Cone 04: 1.5-2.5% Cone 03: 3.5-4.5 Cone 02: 4.0-5.0
Cone 04: 9.0-11.0% Cone 03: 6.0-7.5 Cone 02: 4.5-6.0
Safety Data SheetClick here for web view.
|Plainsman Clays Ltd.|
702 Wood Street, Medicine Hat, Alberta T1A 1E9
Phone: 403-527-8535 FAX:403-527-7508