Low temperature, smooth, medium plastic, off white to white burning, refined high-talc earthenware for modelling or casting. L213 is available in a pugged plastic version and as a casting slip. Both are a 50:50 mix of AmTal Talc and KT#1-4 Ball Clay. Each has a 2.5% addition of calcium carbonate. This recipe is a standard that has been used in hobby ceramics across North America for many decades. The casting version of L213 adds 0.5% bentonite and the throwing one 3.5% bentonite. L213 is the best choice for people who intend to use commercial premixed glazes from companies like Duncan, Mayco, Spectrum, etc. and who need a white burning material.
You can make forms that combine plastic L213 elements from formed and mold-made elements. If you are working with the casting slip also consider using the deflocculated slurry to join sections since its much lower water content produces less shrinkage. However do not expect the same drying performance from L213; slip cast ware typically has much thinner and more uniform wall thicknesses than hand formed ware.
L213 burns very white from cone 06 to cone 2 due to the lack of a glassy phase that darkens iron and the use of special whiter burning ball clay and talc. As a result you can apply a transparent glaze (for cone 06-04) and achieve clean looking ware and colored glazes fire to much brighter shades.
Above cone 2 the fired body color shifts to grey-buff. Still, L213 can be fired much higher without bloating or melting (we have gone all the way to cone 10R), however please experiment in your circumstances to determine how high you can practically fire it.
Since L213 is 50% ball clay (which tends to block venting of water vapor) you must be careful not to fire too fast during early stages. We recommend preheating the kiln overnight to give the ware lots of chance to dry thoroughly.
Commercial brush-on glazes are formulated to fit high-talc bodies (like L213, L212). Talc bodies have high thermal expansion, this puts the squeeze on the glazes (reducing crazing). But this can go too far, glazes can be under excessive compression and shiver off contours or press outward from the inside of ware, cracking it (especially if ware is unglazed or engobed on the outside). We cannot guarantee that any glaze made by another manufacturer will not craze or shiver. Do stress testing (in boiling water:ice water, the BWIW test). Do not assume food safety of brightly colored glazes in your kiln without a leach test (e.g. GLLE test). Consider using transparent or white liner glazes for food surfaces.
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.
Crazing: Functional ware must remain craze-free (crazing is unsanitary and drastically reduces ware strength). Because ware is not crazed out of the kiln does not mean it will not do so with time. Do cycles of a boiling water:ice water immersions (BWIW test) on a piece to test glaze fit (by stressing it to bring out any crazing or shivering tendencies).
Glaze slurry consistency and quality: In freshly mixed or stored glazes that do not have natural thixotropy a secret to achieving even coverage is inducing it by additions of a flocculant. A glaze of the right specific gravity and having a slightly gelled condition goes on to bisque ware evenly, does not drip and dries in seconds. Always screen glazes when first making them (80 mesh). Be alert to any particulate that may appear after storage (e.g. precipitates) and screen again if needed.
For slip decoration and engobes be careful to match the fired shrinkage of the slip with the body. Where we do not recommend a specific engobe recipe use a formula based on the porcelain itself. Add 2% VeeGum or Bentonite (the extra stickiness helps it adhere well to leather hard ware). Be careful about adding fluxes (e.g. frit), this increases fired shrinkage (the mismatch with body can cause flaking) and can compromise opacity.
If you want to develop and mix your own glazes and engobes consider getting an account at http://insight-live.com. You can organize a methodical development program and adopt better methods of testing (e.g. melt fluidity, thermal stress, slip-fit tests).
In our lab we use the following recipe for testing (scale this up to the batch size that you need):
L213C dry 1500 g Water 700 g Darvan #7 8-10 g
Start with the minimum amount of Darvan and mix well.
This recipe should yield a conservative specific gravity of 1.74. We do not suggest adding any more water if it is not fluid enough. Instead add more Darvan to the maximum recommended.
Ball clay:talc bodies have incredible casting properties. This bowl is 13cm across yet has a wall thickness of less than 2mm and weighs only 101g! It released from the mold with no problems and dried perfectly round. And when fired at cone 04-06 it will stay round!
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: 21-22% Drying Factor: A000 LOI: 11-12% Dry Density: n/a
Sieve Analysis (Tyler mesh):
65-100: 0.1-0.2% 100-150: 0.1-0.4 150-200: 1.0-2.0
Cone 06: 1-2% Cone 04: 2-3% Cone 02: 2.5-3.5 Cone 2: 2.5-3.5
Cone 06: 13-15% Cone 04: 11-13 Cone 02: 9-11 Cone 2: 8-10 Cone 4: 9-11 Cone 6: 10-13
Buffstone, L212 and L213. Each has its own clear glaze. G2931L, G2931K and G2931H. L is low expansion (for zero-talc porous bodies like Buffstone). K is intermediate (for moderate-talc bodies like L215, Zero3 stoneware and porcelain). H is high-expansion (for higher-talc bodies like L212, L213).
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