Decorating Porcelain
Today there are many options for putting colorful patterns onto porcelain china. Some, like Decoupage, Water Slide Decals and air-dry paints (Delta Air-Dry PermEnamel) are within the reach of any home crafter.
Others, like Dye Sublimation printing, transfer printing and hand-glazing high-fired pottery require substantial investment in equipment and are best suited to well-capitalized businesses and artists' cooperatives.
The two classic ways of putting patterns onto porcelain, hand-painting and transfer printing, still exist today.
In addition, there is a high-tech version of water slide decals used commercially which consists of screen-printing decals with glazes and applying the decals to the porcelain.
In each case, the pottery is high-fired before decorating to at least cone 6. [ Cone is a measure of heat absorption resulting from heat applied over time. Cone 6 translates to between 2165 and 2269 degrees F (depending on how fast the kiln heats - or ramps - up). ] Such high-firing produces the hard almost-translucent quality of genuine porcelain.
Then the piece is decorated and lightly fired repeatedly to melt and fuse the glazes to the porcelain.
Incidentally, the term "porcelain" has been applied more and more broadly as new techniques developed. Ask any potter to define "porcelain" and he will likely give you the classic definition.
To a potter, genuine porcelain is high-fired (cone 6 or higher) white clay that is at least somewhat translucent. It has a large proportion of kaolin clay, with the remainder being primarily feldspar and silica. This clay composition accounts for the pure white gleam of porcelain.
Artisans who paint porcelain (rather than actually make it) refer to three grades of porcelain: hard-paste, soft-paste, and bone china. They all contain kaolin, but only hard-paste has feldspar and silica and is high-fired. The high temperatures cause the body and the glaze to fuse. When hard-paste porcelain is broken, it is impossible to distinguish the body from the glaze.
Soft-paste porcelain adds ground glass or frit (material for glass that is not yet fused and vitrified) and is fired to between cone 01 and 1 (1999 to 2109 degrees F). Because soft-paste porcelain is fired at lower temperatures, it does not completely vitrify and remains slightly porous. When soft-paste porcelain is broken, you can distinguish a grainy body covered with a glassy layer of glaze.
Bone china has bone ash added to the kaolin and vitrifies (becomes glass-like) somewhere between cone 2 and cone 5 (2034 to 2205 F). Though not as hard as true porcelain, bone china is more durable than soft-paste porcelain. The bone ash greatly increases the translucence of the porcelain.
Finally, go to a tile store and look at their "porcelain" tiles. If you turn them over, you will see base clay ranging from white to brown to gray. The definition of "porcelain" in the tile industry has nothing to do with the clay content or level of firing.
Rather, tile manufacturers define as "porcelain" any tile fired to the point where it absorbs less than 3% moisture.
How Porcelain is Hand-Painted
Porcelain, for its pure white color, is the preferred surface for representational art on ceramic. The painting is done in stages. After a ceramic piece has been high fired, it is covered with an underglaze and lightly fired. The design is drawn or inked onto the glazed surface and painting the design can begin.
The porcelain artist works with one glaze color at a time to keep the colors pure. Each color is fired separately to its appropriate temperature. Over-firing can fade or change the colors and ruin the design. There is as much science as art to the process of porcelain painting. Glazes are selected both for their colors and for their vitrification points. A low-fire glaze can never go under a higher-fire glaze because the higher heat for the overglaze would melt and destroy the underglaze.
Most porcelain artists purchase their glazes in powder form and mix the powder with their choice of oils. Eucalyptus or lavender oils are popular. Safety precautions are important when mixing the powders, since many of them contain lead or other toxic heavy metals.
Oil is preferred as an additive because it adheres better to the glossy porcelain surface than water. By mixing their own glazes, artists can control the consistency and match it to their painting technique. For a design with much detail painting, a slower-drying consistency is normally preferred.
Five to eight layers of glaze are common on porcelain work. The final glaze layers can be anything from real gold or silver accents to a myriad of low fire opalescents or lusters. Because of their low vitrifcation temperatures, such final glazes or trims are not as durable as the underglazes.
This is why you are warned not to put your gold or silver-trimmed china in the dishwasher!
How Transfer Printing on Porcelain is Done
Transferware printing is a form of offset printing in that the printing is not done directly onto the porcelain. A design is engraved onto a copper plate. The plate is inked with glaze and printed onto a piece of tissue paper. The printed paper is then reversed and pressed onto the porcelain, thereby transferring the design in its original orientation.
After inking, the porcelain is low-fired. Overglazes are often applied to protect the transfer from wearing away. Because the designs are engraved on copper, very fine lines and elaborate scenes can be created.
The first designs were Oriental, the most famous being the Blue Willow pattern which depicts the tale of two star-crossed lovers. They flee to an isolated island to escape her arranged marriage but are soon captured by the mandarin. Before they can be executed, the gods take pity and transform them into two doves which are seen staring lovingly at each other at the top of each plate. Yes, this entire story is depicted on each plate!
Others are no less elaborate: historical events; portraits of famous personages; popular tourist spots; elements of nature realistically depicted - such as flowers, birds and insects; and Romantic Landscapes - the proper title denoting that the scene must include a river or lake, a building, mountains, and people with animals in the foreground.
How Porcelain is Decorated Today
Today, designs for porcelain are created and screen-printed onto water slide decals designed to withstand kiln-firing. The printed transfer is soaked until the design can be slid off onto the porcelain and positioned. The piece is then fired in a kiln.
During firing, the transfer medium evaporates and the glaze fuses onto the porcelain just as it would if painted directly and fired. Though this sounds very high tech and automated, there is still as much art as science to the process.
Glazes are tricky compounds. Too much heat and the color can change; not enough and fusion does not occur. Because minerals and precious metals are still components, the consistency of glazes cannot be known until they are fired. Quality control depends largely on the skill and experience of the printer.
In my opinion, the porcelain dinnerware you purchase new today should be considered a work of art and treated the same as if it were a fine antique.
Read The History of Porcelain.
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