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The most beautiful thing we can experience is the mysterious. It is the source of all true art and science, said Albert Einstein. He could’ve been talking about porcelain, because for almost one-thousand years, the art and science of porcelain made it the most mysterious and coveted type of decorative art in the world.
Everyone knew the secret. No one knew the secret. It just depended upon where you lived.
The Chinese began making early forms of porcelain in the 600s, and pure (hard-paste) porcelain in the 1200s. When it started to be sold in Europe, everyone wondered what it was and how it was made. White jade? White gold? Alchemy?
Until Europeans learned the secret in the 1700s, porcelain was the holy grail of the art world. In medieval France, it was believed that a porcelain cup prevented poison from working.
Augustus the Strong, Elector of Saxony and King of Poland, was so infatuated with porcelain that he diagnosed himself with porzellankrankheit (porcelain sickness). He once traded an entire regiment of fully-equipped soldiers for 151 pieces.
Porcelain wasn’t rare in China, but it was still desired. In 1554, the Jiajing Emperor ordered the imperial kilns to make “26,350 bowls and 30,500 plates with dragons on them in blue, 6,900 cups that were white inside and blue outside decorated with blue flowers, 680 large fish bowls decorated with blue flowers on a white background, 9,000 teacups with foliate rims in white, 10,200 bowls and 9,800 teacups decorated with lotus flowers, water plants and fish in blue and white on the outside and dragons and phoenixes passing through flowers on the inside, and 600 libation cups with hill saucers decorated with sea waves and dragons in clouds in blue, and 600 wine ewers of white porcelain.
The following year, he ordered 1,470 more; the year after that, 34,891.
Only the Chinese knew how to make porcelain. Outside of China, the obsession to learn the secret involved kings, kidnappers, alchemists, a Jesuit priest, and one of the longest lasting, world-wide attempts at industrial espionage in history.
Proceed with caution, porzellankrankheit is contagious.
秘 (The Secret) of Porcelain’s Art and Science
Tens of thousands of years ago, humans discovered that objects fashioned from certain types of clay could be mixed with water, dried in the sun or nestled in a pit, and set on fire (1000 °C / 1832 °F). The hardened clay became containers for food and water, tiles, bricks, and art objects.
Ceramics are objects made from clay that become permanently changed when heated. Place a dry lump of clay into a bowl of water and it disintegrates. Fire (heat) it to a certain temperature and, depending upon the type of clay, it changes forever.
There are three types of ceramics: earthenware, stoneware, and porcelain.
The oldest known earthenware is a 15,400-18,300 year-old pottery shard that was found in a cave in China. Clays used for earthenware must be heated to 600-1000 °C / 1112-1832 ° F (higher temperatures melt the clay). To become non-porous, or waterproof, earthenware must be coated with a glaze and refired; the glaze melts and forms a thin glass coating over the surface.
Around 1600-1050 BCE, the Chinese invented the kiln, an insulated chamber where high temperatures could be reached and maintained for long periods of time.
Now a wider variety of clays, like those with heat-resistant impurities, could be used. Fired to 1,100-1,300 °C / 2,010-2,370 °F, they become stoneware – waterproof, usually opaque, and hard.
The first stoneware was made in China around 1400 BCE. Because European kilns were not as efficient and the right type of clay was less abundant, the first stoneware in Europe was made around 1400 CE. (Yes, 2,800 years later.)
In the 600s CE, potters in China began to create wares that were far superior to the other two types – porcelain. It was said to be made of ‘flesh and bone’. Hundreds of years passed before anyone outside of China figured out what that meant.
The ‘flesh’ of porcelain is petunse (below left), or porcelain stone, a mineral that is rich in feldspar (rock-forming minerals that compose about half of the earth’s crust), silica, and flint (a type of hard quartz). The other mineral, kaolin (below right), or porcelain clay, was formed by the weathering and breaking down of certain types of feldspars 80-100 million years ago; it is the ‘bone’. Petunse is reasonably easy to find, but kaolin deposits are less common and are scattered around the world.
When mixed in the right amounts and heated to certain temperatures, the molecular changes that occur create the unique beauty of porcelain. Petunse binds the clay together so it’s hard and translucent. Kaolin lends plasticity and strength so that the clay body can hold its shape. In the heat of the kiln (biscuit firing), they fuse and stick together at points of contact that leave open areas. Heated a second time (glost firing), kaolin becomes a glassy-gel that fills the spaces. The resulting ceramic is now called ‘hard-paste’ porcelain. (Imagine different piles of rocks on the ground that, in the heat of day, begin to stack and perfectly align themselves end-to-end to form a wall. The next day, under the sun’s heat, a similar pile of rocks melts into a glassy mortar that seeps between the rocks into any open spaces.)
So many things can go wrong. The three substances (quartz and feldspar from the petunse and the kaolin clay) need to be purified and then mixed in exactly the right amounts. Too much petunse makes the clay too stiff to work with. Too much kaolin and the clay body will sag, shrink, collapse in the kiln.
From Mine to Magnificent
Jingdezhen has the perfect location. Pine forests provide fuel for the kilns. Gaoling mountain, 25 miles away, is one of the few areas in China that had pure kaolin. Other nearby areas are rich in petunse. A river connects them all.
The process for making porcelain was traditionally carried out by seventy-two people, each doing a different step. There are “six categories of decorator, three of specialists in packing kilns, three for firing kilns, mold-makers, carpenters for crates, basketmakers, ash-men for cleaning away the residue after a kiln-firing, compounders for clay and grinders for oxides, experts in how to place pots inside saggars, others to place them inside a kiln, men who can balance a board of stacked cups over each shoulder and navigate a rainy street full of people. And there are the dealers and merchants and scholars, officials and accountants, label writers, doorkeepers, guards for the imperial porcelain factory.”*
First, the petunse was mined –
– and then delivered to mills along the river bank where water-powdered levers with stone heads shod with iron pulverized the rock. During the wet season, an official in 1576 wrote, “the noise of tens of thousands of pestles thundering in the ground … kept me awake all night.”
The bits were then crumbled into water to make a slurry and impurities were removed. It was then passed through a series of sieves and strained through bags made of double layers of silk.
The remaining sludge was dried and formed into bricks. Petunse means ‘little white brick’ in Chinese.
Nearby, kaolin was also mined, and its fine white clay was collected. The highest quality kaolin was reserved for imperial use; those caught possessing kaolin without official permission were punished heavily. Exhausted mines were sealed shut so that no one could steal the scraps.
Petunse and kaolin bricks were loaded onto boats and delivered to Jingdezhen. While spying on the process, a Jesuit priest wrote that a “never-ending line of boats” loaded with petunse and kaolin came down from the hills, “up to three rows of boats, one behind the other.” He noted the great mounds of chipped, defective and broken porcelain piled high along the river bank.
Petunse and kaolin were pulverized together, sometimes by the feet of water buffalo, in proportions that vary according to the grade of porcelain to be produced. Equal quantities for the best; two-thirds petuntse to one-third kaolin for everyday ware.
The mix, called a ‘paste’ or ‘body’, was then thrown onto large stone slabs, worked with iron spades –
– and then kneaded and wedged by hands and feet until it was ready –
– to be shaped on the potter’s wheel. Assistants spun the wheel with their hands and feet and sticks. The potter must keep in mind that porcelain will shrink 10% in the kiln.
An assembly line of master potters further refined the objects.
Large pieces required a team to shape them.
Each piece was placed in a saggar, a clay container that protects the item from being touched by flames.
The saggars were loaded into kilns. Some kilns were designated to produce porcelain only for the imperial family. Others made common dinner sets for domestic markets.
Dragon kilns, which were long and thin and steep, were used when a large number of wares needed to be fired at the same time. Fueled by wood or coal, firing began at the bottom and moved up the slope. The necessary temperature to create porcelain is 1,200-1,400 °C / 2,200 – 2,600 °F. (To put this in perspective, steel melts at 1371 °C!)
Because firing was uneven across the length of the kiln, the temperature in the elevated chambers rose slowly and produced better pieces. As the hot air rose up the tunnel, the ‘dragon’s belly’ rumbled and crackled.
In the largest dragon kilns, 100,000 pieces could be fired at one time.
After 20 – 30 hours of firing, the kiln and its contents were left to cool for several days to a week to a month, depending upon the size and delicacy of the pieces inside. Fine cracks (crazing) form if the ware is cooled too quickly. Out of the kiln, the body now looks like white marble.
Still unfinished, the porcelain was then covered with a glassy compound, or glaze, and fired a second time. The heat fuses the coating to the porcelain’s surface and forms an extremely smooth, hard surface.
If the body of the porcelain and the glaze expand and contract at different rates, a crackled pattern forms. Sometimes crackles were intentionally created in desired sizes and patterns.
The porcelain was then decorated by various techniques.
If a painted decoration was applied before glazing (‘underglazing’), it must be fired again to set it. Only cobalt blue and copper red paints can withstand the high temperature needed for the glaze. Underglaze decoration cannot be felt on the porcelain’s surface.
Enamel paints are applied after the ware has been glazed (‘overglazing’). Because the enamels are fired at a lower temperature and do not sink into the glaze, the decoration can be felt on the surface.
The final product was then packed,
delivered to ports,
and shipped to other parts of China and Europe.
How did porcelain from China first find its way to Europe?
Why do some of the most spectacular examples involve chickens?
How did a Jesuit priest become a spy?
And how did a kidnapped alchemist turn a friend’s death into a golden opportunity?
Click here to learn more about porcelain in:
Top image: Saucer, c. 1750; Hard-paste porcelain with enamel decoration; China; 1 × 4 7/8 inches; Philadelphia Museum of Art
– Meighan Maley
* Edmund de Waal. The White Road – Journey into an Obsession. Farrar, Straus & Girous, New York. 2015
Philadelphia Museum of Art Website