High temperature, smooth, medium plastic, vitreous, white firing, refined body for reduction and oxidation porcelain functional ware. P600 is intended to provide the most porcelainous nature possible in a plastic vitreous cone 10 white body made from North American kaolins (#6 Tile and EPK). It is fluxed with nepheline syenite and has 23% silica and we add some micro-fine bentonite to increase plasticity. It is a legacy product, P700 is has better firing and working properties.
The recipes of P600 and H570 are too similar to justify making both bodies, H570 being the superior of the two (P600 is about 50% Tile #6 plastic kaolin, H570 simply substitutes about 20% of that for M23 Ball clay). P600 is a little more vitreous than H570, if that is important to you then we recommend the use of P700. If cost is an issue, another option is to wedge some P300 into H570.
P600 is a smooth and very slick fine grained body. Its kaolin-only nature impart a different plastic character than white stonewares (which also contain ball clay). P600 is plastic, but not as plastic as P700 or H570.
Drying: Porcelains do not dry as well as stonewares or bodies with particulates. You will get the best results if the clay is not too soft, ware is not too thick, contours are smooth, wall thicknesses are even, joins are few and done with thick slip, the degree-of-wetness in all parts of a piece is kept equal throughout all stages of drying. Large pieces are best made on plaster bats so the bottom can stiffen with the walls. The worst drying performance will occur with thick ware made from very soft clay, the use of non-absorbent bats, where vessel walls are thick at the bottom and thin at the lips or edges, walls are of uneven thickness with lots of joins or abrupt angles (giving cracks a place to start) and where drying is uneven (e.g. lips and edges are permitted to stiffen early on while lower sections remain soft). Large, flat plates are the most difficult shapes to dry, it may be necessary to stretch the time out to a month or more to achieve the even drying needed for success.
Although P600 is not a true translucent porcelain, it does vitrify to a very pleasant silky surface and does display a measure of translucency on thin pieces. It does have some tiny black specks, not normally big enough to come through glazes (from the Tile #6 kaolin it employs). P600 is not nearly as white and clean as P700. P600 normally reaches zero absorption at cone 10 and 10R. If ware made from it has a shape that is not structurally strong (i.e. a straight sided cylinder, goblets with flared bases, overhung bowls) it is likely to warp, especially if set on kiln shelves that are not flat.
P600 is a variation on the widely used '25% Porcelain' recipe. However it uses only kaolin rather than a kaolin:ball clay mix. It thus has a lower silica content and so crazing may occur if your glaze has a high thermal expansion.
The body fires to a high strength, a strength that can be severely compromised if a glaze is under excessive tension. We recommend that you stress-test a piece of ware using a boiling water:ice water test. Ware should be able to survive several two-minute cycles before trouble appears.
If you wish to use slip on your ware, make it from a base of P600 for the best possible drying shrinkage/fired shrinkage match.
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. Some recipes rely on high melt fluidity to encourage crystallization and variegation (often because of inadequate SiO2 and Al2O3 or containing Gerstley Borate 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.
Consider using our G1947U glossy or G2571A matte base recipes, just add colorants, opacifiers, variegators (you will find links to much more information and pictures about these). If you have a recipe that is troublesome, consider transplanting its opacifiers, colorants and variegators to these bases instead. http://ravenscrag.com and http://albertaslip.com also have many recipes that work well on porcelains.
Crazing: Functional ware must remain craze-free (crazing is unsanitary and drastically reduces ware strength). Even though ware may not be crazed out-of-the kiln it may 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).
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 one 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 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).
We do not supply thermal expansion values. If a chart is supplied here, please view it only as a way to compare one body with another. Please note that, although you may calculate the thermal expansion of a glaze, this cannot be done for clay bodies since they do not melt. The best way to fit glazes to clay bodies is by testing, evaluation, adjustment and retesting. For example, if a glaze crazes, adjust its recipe to bring the expansion down, fire a glazed piece and thermal stress it (using an IWCT test, 300F into ice-water). If it still crazes, repeat the process.
Drying Shrinkage: 5.0-6.0% Dry Strength: n/a Water Content: 22.0-23.0% Drying Factor: C110-C120 Dry Density: n/a
Sieve Analysis (Tyler mesh):
+100: 0.0-0.1% 100-150: 0.1-0.3 150-200: 0.2-0.8 200-325: 3.0-5.0
Cone 8: 7.0-8.0% Cone 10: 7.0-8.0 Cone 10R: 7.5-8.5
Cone 8: 1.0-2.0% Cone 10: 0.0-0.5 Cone 10R: 0.0
Compared to Others
The decline of the ceramic industry in North America has impacted the price, availability and quality-for-ceramics of raw materials from which porcelains are made (especially ball clays and kaolins, which have seen increases in soluble salts, foreign particles and iron specks). In addition, we do not have filter-pressing, pre-mixing and stainless-steel pugging equipment (these would drastically increase prices). While you cannot make Wedgewood-quality ware it will be far whiter and cleaner than our stonewares. Notwithstanding that, be aware that transparent glazes carry a chance of isolated specks using our standard porcelains, it is better to use white and colored glazes on these. If you absolutely need a clean, white, translucent porcelain consider using our premium products, Polar Ice and P700 (they cost more but you get much more). We are also developing engobes for low, middle and high temperature ranges, using these you can apply a porcelain-like surface of almost any color at leather hard stage and completely hide the underlying stoneware. These engobes are so opaque that a white one can completely mask a black body underneath using only one coat. So, if you can master their use (there is lots of documentation here) many new design opportunities will offer themselves.
Soda fired P600 vessel by Heather Lepp. The soda-vapour atmosphere of the kiln glazed one side of the vessel early enough in the firing to trap carbon under a crystal-clear glass. Often such glazes are crazed, but this one likely is not because the body contains 25% quartz, giving it a high thermal expansion. The other side of the piece exhibits tones of red, brown and yellow on the bare, vitreous porcelain surface, this is characteristic of "flashing".
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|Plainsman Clays Ltd.|
702 Wood Street, Medicine Hat, Alberta T1A 1E9
Phone: 403-527-8535 FAX:403-527-7508