Plainsman Polar Ice, P300, M370 and M340 with G2926B Whiteware transparent glaze on the porcelain (G2916F Stoneware transparent on the M340).
This body employs New Zealand Halloysite, a super-white-burning kaolin from New Zealand. To that it adds the highest quality ceramic plasticizer available, making it the most plastic clay body you likely have ever used (of any kind)!
Disclaimer: Please match your expectations to the reality of what Polar Ice is. It is expensive compared to our other bodies because of the cost of materials and difficulty of production. But Polar Ice is not nearly as expensive as it would be if we were to purchase special filter-pressing, slurry-screening and pre-pugging equipment to guarantee top quality. We actually make it my mixing the powder and water right in the pugmill! Why? It is too plastic to be slurry-mixed (without huge quantities of water), too sticky to be filter pressed or extracted from a prepugger! Our production method is the only way it is possible. But that comes at a cost: Some fired specks and hard chunks. But if you are willing to make a commitment and adjust your expectations, you will be able to make ware that was once impossible for potters.
At times you may find surface discolouration on the slugs from bacteria growth (if the material is old).
Using Polar Ice is more of a commitment than other bodies. Compromises are required, expectations are different.
Plasticity: Polar Ice is extremely plastic. Others claim to be plastic, but they use the word in a relative sense (meaning "a little less short than other really flabby porcelains"). However Polar Ice is only plastic when stiff enough (do not attempt to use Polar Ice if it is too soft).
Stiffness: To properly pug it we must run it too soft (you will notice this if you buy a newer run). However, it will stiffen over time. Consider keeping a box of stiffer material around so you can wedge it together will softer to get the right consistency. Failing that, reduce water content on a very clean plaster surface or leave a lump under a cloth over night or longer. It is imperative to wedge different stiffnesses together well or throwing will be adversely affected.
Polar Ice is not ready-to-use out-of-the-box. It comes out like a rock and then softens to a sticky, unusable mass when wedged! Flatten pieces on clean plaster bats to dewater for a while, then wedge thoroughly (repeat until it is no longer sticky). When it is wedged really well and the stiffness is right it will want to go taller and thinner than any clay you have ever thrown!
Stickiness: This is the most prominent side effect of the plasticity. It will stick to your hands, to the table, to the cutting wire, anything that touches it. During trimming it will stick back to itself and tools. If you attach ware to the wheelhead with water to trim, it will stick fast. After trimming it balls up under your fingers if you attempt to round corners by pressing on them. However when stiffened to optimal throwing stiffness, it is much less sticky.The stickiness is an asset when joining, the slip glues it well (if adequate pressure is applied).
Drying: Thin ware of even thickness, few joins and dried under conditions where degree-of-wetness is always kept the same throughout, these will dry the best. Thick ware of uneven thickness, lots of joins and dried unevenly will crack the most. Drying pieces under plastic, without a cloth over them, will often produce issues.
We have had consistent results firing to cone 6 oxidation. We formulated it so that a thin-walled, vertical-sided mug with flared lip will not pull to an oval-shaped rim during firing (by the weight of the handle). Notwithstanding this, in our lab we can get translucency down to cone 4. We have fired it to cone 8 oxidation (with more warping) and cone 10 reduction (with surprisingly good results and little warping). Very durable and strong ware can be made using this body.
To get maximum translucency it is not necessary to fire over cone 6. The casting version is not quite as translucent as the throwing version (however the walls of cast piece are generally much thinner). You can enhance the translucency of the casting version by additions of Ferro Frit 3110 (e.g. 5%).
Impeccable cleanliness is needed to minimize fired specking for transparent glazes. At the same time, we cannot guarantee a completely speck-free result. This body is not filter pressed. While this background mug is speck free, the other two are not. The blue speck on the mug rim (right) is likely contaminant picked up during the process. The small black ones on the left could have come in the material.
To get the best defect-free surface please consider using a drop-and-hold firing schedule, for example the PLC6DS schedule. If crystallization during cooling is not an issue, glazes will give optimum results if slow-cooled also (e.g. the C6DHSC schedule).
Polar Ice fired bars (cone 4-8 oxidation bottom to top). At cone 8 the body is very glassy and beginning to melt.
Commercial brush-on glazes offer many colors and surfaces. For functional ware check for glaze fit (vital for quality functional ware). Do not assume food safety of brightly colored glazes in your kiln and with layering without a leach test (e.g. GLLE test). Consider using a transparent or white liner glaze for food surfaces.
Mixing your own glazes is practical (with our clear guidelines even beginners can make dipping glazes that go on silky smooth and evenly and dry in seconds). If you already do this using recipes from the web, be careful. High-feldspar glazes (having more than about 35%) often craze. Ones that rely on high melt fluidity to encourage crystallization and variegation (often because of excessive Gerstley Borate, lithium carbonate, zinc or Frit), view these with suspicion for leaching and cutlery marking; test them well (also test the additionless versions). Be suspicious of any glaze not having good documentation.
The best approach is to begin with a good transparent base you understand and that fits. We supply (as products and recipes) G2926B glossy whiteware and G2934 matte frit-fluxed bases. Their documentation describes how to mix, use, fire and adjust them and showcases stain, color and variegator additions to create an infinite number of effects. The former, G2926B, may not have a enough melt fluidity to create non-food-surface reactive visual effects with certain colors and variegators. G3806C fluid-melt recipe is an alternative (but check for crazing). These pages also reference other base glazes that might be of interest.
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).
Thixotropy: Many people mix their glazes the traditional way, just adding water until the slurry appears to be the right viscosity for dipping. However, if you want better application properties for one-coat dipping, consider creating a thixotropic slurry. Thixotropic glazes are creamy because they have been thinned and then gelled by the addition of a flocculant. They go on evenly, hang on without dripping and dry quickly. Achieving (and maintaining) this state involves targeting a specific gravity (usually around 1.43) and adding epsom salts (1-2g/1000g of powdered glaze).
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).
Polar Ice casting requires extra care, good mixing and some compromise to get a slurry of the right consistency (it is important to understand the principles of deflocculation, be able to measure specific gravity efficiently and have a good propeller mixer). This contains a plastizer to impart the plastic strength to better enable pieces to shrink and pull away from the mold (this requires double the normal amount of Darvan and lengthens casting time considerably, M370 is easier to cast and mix). Polar Ice pieces will warp on firing if they are thin or shapes are unstable.
Because of the magic of defloccualtion you can mix all this powder into that little bit of water! This 20 Kg bag of porcelain needs only 9 Kg of water in the bottom of that pail. The secret is that the water contains a small amount of Darvan, it makes the particles repel each other electrolytically enabling a fluid slurry with only a little more water than is in a throwing clay!
Casting properties depend on proper deflocculation. Assuming viscosity and specific gravity are good, and you have good molds, the slip will drain well and wall thicknesses will be even. Watch out for powdery or dry-feeling pour surfaces (shortly after pouring out the slip), these mean over deflocculation.
Recipe Used in the Plainsman Lab
67.3% Polar Ice Casting Mix Powder
32% Water (distilled recommended)
0.7% Darvan No. 7
This is a 100-total recipe, that means 67.3 parts-by-weight of powder and 32 parts-by-weight of water.
This should produce a specific gravity of around 1.7 with a Ford Cup viscosity of 40 seconds (Laguna Viscometer reading of 140 seconds). Polar Ice cannot tolerate over-deflocculation well, that is why we are using a conservative recipe with a lower-than-typical specific gravity (contact us if you have issues). If your slip is not flowing well enough consider adding more water rather than more Darvan.
Water and Darvan percentages are not cast-in-stone, adjust as needed. Add 90% of the Darvan to the water and mix it in. Then add the powdered body mix to the water under a propeller mixer. It might appear that it is impossible to get that much powder into the available water, but that is the magic of the Darvan. Mix at least 15 minutes. If you cannot get the last of the powder in, add the rest of the Darvan. Do a preliminary assessment:
If you are not doing alot of production and can tolerate your molds getting wetter (and longer mold extraction times), adding water to the slurry will not be a problem (although too much may cause settling issues). Remember also that warm slip will flow better than cold.
You can make about 1 US gallon from 5000 grams of powder. You can make about 1 Canadian gallon from 6300 grams.
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: 5.5-6.5% Dry Strength: n/a Water Content: 21.0-22.0 Drying Factor: C130
100-150: 0.1-0.3 150-200: 0.5-1.0
Cone 5: 0% Cone 6: 0% Cone 7: 0%
Competing NZ Porcelains from Other Manufacturers: Polar Ice is likely very different. We are pretty sure you have never used anything like this before!
Polar Ice casting succulent plant pot and tray. The glaze is G2926B with 10% Mason 6304 and 2% Zircopax.
21 mugs made from 1/2 box of clay, 10 kg ( (all scrap was reclaimed). Polar Ice is plastic and you can make more pieces because it can be thrown thinner than most other clays. These have a weight-to-capacity ratio of 1.09 (each 1 gram of fired porcelain can contain 1.09 grams of water). This is the highest of any of our products.
|Plainsman Clays Ltd.|
702 Wood Street, Medicine Hat, Alberta T1A 1E9
Phone: 403-527-8535 FAX:403-527-7508