The whitest, most translucent yet most plastic porcelain we make.
Three porcelains and a buff stoneware with transparent base glaze at cone 6.
On the left is Plainsman M370, right is Polar Ice.
This body employs New Zealand Halloysite, the whitest burning kaolin available. To that it adds the highest quality ceramic plasticizer available. The full throwing version is a no-compromise product. It is the most translucent, the strongest, the whitest and the most plastic clay body you likely have ever used! At the same time it dries well.
Disclaimer: The price of Polar Ice is a reflection of how expensive its materials are and how difficult it is to pug. Notwithstanding that, we do not have filter-pressing, pre-pugging and stainless-steel pugging equipment (if we did the price would be far higher). Even if we did have such equipment this material would be too sticky to filter-press or pre-pug. This means that there may be some isolated specks, we must pug softer and thorough wedging is required to remove laminations. Still, it is far whiter and cleaner than any other product we make.
It is like a rock in the box, but softens dramatically when you cut a piece and start to move it.
Polar Ice has extremely high plasticity (to properly pug it we must run it too soft). Others claim to be plastic, but they use the word in a relative sense (meaning a little less flabby than that other really flabby porcelain). Do not attempt to use Polar Ice if it is too soft (stiffen it before use to experience its full plasticity). To reduce the water content wedge it and flatten down onto a very clean plaster table or large bat (or you may be able to leave a lump under a cloth over night or longer).
The most prominent side effect of the plasticity is its stickiness, this body is extremely sticky. 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 there also. After trimming it balls up under your fingers if you attempt to round corners by pressing on them. However if you stiffen the body to optimal throwing stiffness, it will be much less sticky.
Even though it is very plastic, it dries well (if not too soft).
The keys to successful drying are stiffening the clay before use (if needed, see info above) and drying ware evenly. In the picture shown here, of 21 mugs made, only one had an S-Crack (it was the first thrown off the hump). The rest do not have the slightest crack, even around the handle join at the bottom (the handles were simply slipped and pressed on using pressure only). Again, dry evenly. At no time during the process from throwing to dry should one part of a piece be stiffer than another. During final drying cover ware with cloth that can be wrapped around under the board on which the ware sits to guarantee no draft can enter.
We only guarantee consistent results when it is fired close to cone 6. We formulated it so that a typical vertical walled mug with flared lip will not pull to an oval-shaped rim during firing (by the weight of the handle). Use cones in your kiln to verify that your controller is going to exactly cone 6. Notwithstanding this, in our lab we can get translucency down to cone 4 and have gone to cone 10 (although severe sagging will occur there). Very durable, strong and translucent ware can be made using this body. Thin pieces will still be resistant to warping during firing even though it is highly vitreous.
Again, do not fire over cone 6 unless you have tested thoroughly. Do not trust cone-fire mode on an electronic kiln controller without verification of a cone in the firing. If you finish a cone fire program with a soak, your kiln will almost certainly over fire. If your kiln is over or under firing (according to the cones you place within), compensate somehow. Consider manually programming each step of the firing. Or compensate by: 1) Using a preset to fire one or one-half cones lower or higher as appropriate. 2) Adjust hold time at the end to fine tune the fall of the cone.
Impecable cleanliness is needed if you plan to use a transparent glaze. One contaminant particle (e.g. iron or cobalt) can leave a speck (as shown here).
Use a high quality transparent glaze. Industrial transparents with perfect fired surfaces are frit based (they do not employ Gerstley Borate), that is what is needed for this. Although you can just dip ware in a clear glaze of your usual fluidity, pieces look best when the transparent glaze is thinner and of even thickness. We have found that a secret to achieving this is preparing a more-fluid-than-normal glaze slurry and flocculating that to gel it slightly. See the glazes page for more information on this.
Our M370 base transparent recipe (G2926B) works well on Polar Ice and showcases its translucency (see the Glazes page). Getting a high quality transparently-glazed surface will require much closer attention to all aspects of your process than with stonewares. The M370 glaze has a lower thermal expansion (less likely to craze) but the M340 one fires a little more brilliant. Do a boiling water:ice water test to check for crazing in your circumstances. These glazes also react differently to some stains, the glazes information page shows samples using many different stains. Screening through 80 mesh is necessary for any glaze you use, but especially mattes, impurities are much more likely to cause noticeable specking and imperfections on a body like this. Some glazes will give much better results if ball milled.
Like the plastic version of Polar Ice, do not compare this with other casting bodies you may have used. This requires much more care and better mixing to deflocculate and get the slurry to the right consistency (however it may very well cast faster and thinner that others). Polar Ice Casting will also warp on firing if pieces are thin (of course you are likely using it for that very purpose, to make thin ware, so it is up to you to make stable shapes that are small enough to fire successfully).
Note: The first run of Polar Ice casting mix contained 1% standard bentonite to give it strength to pull away from the mold. That mix performed well using a mix of 70% powder, 30% water and 0.34% Darvan 7. However subsequent runs switched to 1% VeeGum (it burns whiter, imparts even more plastic strength and gives better translucency). However to deflocculate this requires more water (thus a lower specific gravity) and double the amount of Darvan. While this might not seem desireable, you will find its ability to cast very thin pieces (as little as 1 mm) is outstanding. However before deciding on a casting process in favor of throwing to achieve thinner ware remember one thing: Standard Polar Ice of the right stiffness can be thrown very thin (it is not non-plastic and flabby like other super-white porcelains).
Can you mix all this powder into that little water? Yes! This is a full 20 Kg bag of powder and only 9 Kg of water in the bottom of that pail. But the water contains 200 grams of Darvan, it is the magic, it makes the particles repel each other. It enables making a liquid with only a little more water than is in a throwing clay! Click here to learn more about the magic of deflocculation.
Polar Ice Casting (not quite the same recipe as plastic Polar Ice, it has less VeeGum) has very good casting properties (but only if properly deflocculated). Pieces with wall thickness of as little as 1mm can be cast (with 1 minute set time) and they will still pull away from the mold. You even use heat-lamps or fans to get mold extraction within minutes of pouring. For very thin pieces, use a very sharp knife when cutting away excess around the rim (to prevent splitting). Assuming the 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
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 (of course you also need a good mixer that can run continually and put enough energy into the slurry that its temperature will actually increase). Mix at least 15 minutes (the mixer needs to be powerful enough to pull a good whirlpool, but it should not suck air into the slurry). 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 will not be a problem (unless there is too much in which case it may settle out). Remember also that warm slip will flow better than cold.
You can find information on the mixer we use in our lab at http://digitalfire.com/4sight/education/a_one-speed_lab_or_studio_slurry_mixer_361.html.
You can make about 1 US gallon from 5000 grams of powder. You can make about 1 Canadian gallon from 6300 grams.
Drying Shrinkage: 5.0-6.0% Dry Strength: n/a Water Content: 21.0-22.0 Drying Factor: C130
Sieve Analysis (Tyler mesh):
100-150: 0.1-0.3 150-200: 0.5-1.0
Cone 5: 8.0-9.0 Cone 6: 8.5-9.5 Cone 7: 8.5-9.5
Cone 5: 0% Cone 6: 0% Cone 7: 0%
Compared to Others
Competing NZ Porcelains from Other Manufacturers: Polar Ice is likely very different. We are pretty sure you have never used anything like this before!
Safety Data SheetClick here for web view (format adheres to Globally Harmonized System of Classification and Labelling of Chemicals - GHS)