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.
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.
P600 demands more than the usual attention during drying, especially on difficult shapes (like large flat plates). Time is required to remove all the water since the bentonite and #6 Tile kaolin resist water penetration. If you need to join sections, be sure to follow good practice (i.e. use as much pressure and lateral movement as possible when joining, dry pieces evenly, avoid making ware with an uneven cross section.
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 transparent or white liner glazes 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). 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).
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: 5.0-6.0% Dry Strength: n/a Water Content: 22.0-23.0% Drying Factor: C110-C120 Dry Density: n/a
+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
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".
|Plainsman Clays Ltd.|
702 Wood Street, Medicine Hat, Alberta T1A 1E9
Phone: 403-527-8535 FAX:403-527-7508