| Today there are many options for putting | | | | composition accounts for the pure white gleam |
| colorful patterns onto porcelain china. Some, | | | | of porcelain. |
| like decoupage, waterslide decals and | | | | |
| air-dry paints like Delta Air-Dry PermEnamel | | | | Artisans who paint porcelain (rather than |
| are within the reach of any home crafter. | | | | actually make it) refer to three grades of |
| | | | porcelain: hard-paste, soft-paste, and bone |
| Others, like dye sublimation printing, | | | | china. They all contain kaolin but only |
| transfer printing and hand-glazing high-fired | | | | hard-paste has feldspar and silica and is |
| pottery require substantial investment in | | | | high-fired. The high temperatures cause the |
| equipment and are best suited to | | | | body and the glaze to fuse. When hard-paste |
| well-capitalized businesses and artists' | | | | porcelain is broken, it is impossible to |
| cooperatives. | | | | distinguish the body from the glaze. |
| | | | |
| The two classic ways of putting patterns onto | | | | Soft-paste porcelain adds ground glass or |
| porcelain, hand-painting and transfer | | | | frit (material for glass that is not yet |
| printing, still exist today. In addition, | | | | fused and vitrified) and is fired to between |
| there is a high-tech version of waterslide | | | | cone 01 and 1 (1999 to 2109 degrees F). |
| decals used commercially which consists of | | | | Because soft-paste porcelain is fired at |
| screen-printing decals with glazes and | | | | lower temperatures, it does not completely |
| applying the decals to the porcelain. In each | | | | vitrify and remains slightly porous. When |
| case, the pottery is high-fired before | | | | soft-paste porcelain is broken, you can |
| decorating to at least cone 6. [Cone is a | | | | distinguish a grainy body covered with a |
| measure of heat absorption resulting from | | | | glassy layer of glaze. |
| heat applied over time. Cone 6 translates to | | | | |
| between 2165 and 2269 degrees F (depending on | | | | Bone china has bone ash added to the kaolin |
| how fast the kiln heats - or ramps - up).] | | | | and vitrifies (becomes glass-like) somewhere |
| Such high-firing produces the hard | | | | between cone 2 and cone 5 (2034 to 2205 F). |
| almost-translucent quality of genuine | | | | Though not as hard as true porcelain, bone |
| porcelain. Then the piece is decorated and | | | | china is more durable than soft-paste |
| lightly fired repeatedly to melt and fuse the | | | | porcelain. The bone ash greatly increases the |
| glazes to the porcelain. | | | | translucence of the porcelain. |
| | | | |
| Incidentally, the term "porcelain" has been | | | | Finally, go to a tile store and look at their |
| applied more and more broadly as new | | | | "porcelain" tiles. If you turn them over, you |
| techniques developed. Ask any potter to | | | | will see base clay ranging from white to |
| define "porcelain" and he will likely give | | | | brown to gray. The definition of "porcelain" |
| you the classic definition. To a potter, | | | | in the tile industry has nothing to do with |
| genuine porcelain is high-fired (cone 6 or | | | | the clay content or level of firing. Rather, |
| higher) white clay that is at least somewhat | | | | tile manufacturers define as "porcelain" any |
| translucent. It has a large proportion of | | | | tile fired to the point where it absorbs less |
| kaolin clay, with the remainder being | | | | than 3% moisture. |
| primarily feldspar and silica. This clay | | | | |