Chipstone’s Resident Biophysicist—Professor Temple Burling, Part 2

The Chipstone Foundation’s previous post introduced you to Temple Burling, our resident biophysicist. This post continues his story as he recounts his experience with a blue and white teabowl in Chipstone’s collection.

At the end of my last post, I found myself asking: “How did a porcelain tea-cup with an Asian inspired shape and decorative scheme come to be made in eighteenth-century America?”

This cup is a container for tea, but, as it turns out, the cup also overflows with wonderful stories that partially answer this question. These stories combine science, history, technology, commerce, and cultural exchange, making the cup a slice of a long and fascinating history of porcelain–from its invention in China in the 7th century, to the mania for porcelain collecting by European aristocrats beginning in the Renaissance and exploding during the 18th century.

Porcelain wares from China first arrived in Europe in small numbers via the Silk Road, and in much larger quantities by ship from the 16th century onward. From their first encounters with the material, Europeans were fascinated and mystified by Chinese porcelain. The properties of Chinese porcelain were unmatched by any European ceramics prior to the 18th century. The Chinese porcelain wares exported to Europe were and are without decoration, nearly pure white. They have a glasslike translucency and, even without glaze, are impermeable to water. They are extremely hard, comparatively durable, and make a clear, resonant sound when struck. Even the best European ceramics of the time lacked such refinement when compared to their imported Chinese counterparts.

For more than two centuries after they first encountered porcelain, Europeans had no idea how to make it themselves, despite many efforts to unlock the secrets of its production. Porcelain’s exquisite physical properties, along with the mystery surrounding its manufacture, made porcelain a truly luxurious material, rivaling gold in value among the few European connoisseurs who had the means to procure it. The Chinese producers of export porcelain were well aware of the value placed on their wares, and closely guarded the secrets to making it.

Modern chemical and physical analysis reveals to us that Chinese porcelain from this time consisted primarily of a mixture of two materials, kaolin clay and ground petunse stone. Pure kaolin clay is white in color, owing to the absence of organic and metallic impurities found in colored clays such as those used to make terra cotta or earthenware. Taken together, this porcelain formula consists essentially of physically and chemically weathered granite rocks. Granite is an igneous rock that forms from slowly cooled magma composed primarily of the three most abundant elements in the earth’s crust–oxygen, silicon, and aluminum. Ceramic objects made from the porcelain clay mixture can be fired at very high temperatures (upwards of 1300°C) without deforming. Firing at such high temperature leads to extensive vitrification (glass formation) of the silica component of the porcelain mixture, which in turn leads to porcelain’s translucency. (As a scientist, I can’t help but note the delightful point that during the firing process, porcelain and indeed all ceramics become, in essence, sculpted metamorphic rock.)

The secret to Chinese porcelain’s marvelous physical properties lay in the fortuitous combination of high firing temperatures and optimal clay composition. Before the 18th century, Europeans were unable to reproduce this combination in their kilns or clay mixtures. At first glance this may seem puzzling until we remember that prior to, and indeed well into the 18th century, the European understanding of what we now call chemistry was limited in great part to the four Aristotelian elements, earth, air, fire and water; and to the practice of alchemy. The European potters lacked both the analytical means to match the chemical combination of clays found in Europe to those used in China, as well as the ability to accurately measure and compare the firing temperature of their kilns with those of the Chinese potters. Thus constrained, the Europeans were largely in the dark and limited to trial-and-error as their means to unlock the secret of porcelain. Success proved illusive until 1708 in Dresden, more on this in a moment.

Along the way Europeans developed several significant advances in ceramic technology and styles that were able to capture some of the aesthetic qualities of Chinese porcelain. These include so called “Medici Porcelain,” developed in the late 16th century, and Dutch tin-glazed earthenware or Delftware, which originated in the 17th century. Neither of these is considered true Chinese porcelain, because the physical and chemical compositions of these wares are quite different from kaolin clay-based ceramics. For example, the white color in Delftware results from the presence of tin in the glaze. The tin glaze, which is opaque rather than translucent in Delftware, covers the red oxidized iron color of the underlying fired earthenware clay. Nevertheless, both Medici porcelain and Delftware share the iconic blue-and-white ceramic aesthetic that is as familiar to us today as it was in the 18th century.

Our story takes us next to Dresden in 1708, at the court of Augustus the Strong (1670-1733), Elector of Saxony, and later King of Poland. Augustus was a prodigious collector, obsessed with porcelain, and he spent huge sums to amass one of the greatest collections of porcelain in Europe. As you can imagine, he was quite keen to unlock the secret of porcelain, both to satisfy his insatiable hunger for the stuff, and to reduce the vast outflow from state coffers to pay for it.

He enlisted in this task two very talented men of the early Enlightenment: the scientist Ehrenfried von Tschirnhaus (1651-1708) and the alchemist Friedrich Böttger (1682-1719). Tschirnhaus brought understanding of improved kiln technology; Böttger, a systematic and analytical understanding of the properties of combining materials at high temperature (this would have been the stock-in-trade of any alchemist of that time). The two had access to a local supply of white clay that turned out to be kaolin. Böttger performed a series of tests in Tschirnhaus’ high temperature kilns using various ratios of native kaolin and alabaster. The results of these experiments resulted in the first true porcelain produced in Europe. This so-called “hard-paste” porcelain matched the material properties of Chinese porcelain, and the long-sought secret of porcelain had been revealed. In due course, the first European porcelain factory was set up in nearby Meissen. The well-known company produces porcelain to this day.

The secret to porcelain that had been guarded for so long in China was protected for only a decade or so in Dresden and Meissen. By 1750, porcelain was being produced at multiple sites across Europe. Porcelain wares and figures were eagerly sought by widening circle of consumers. In Europe, the material was associated with Asian exoticism and mystery along with the rational/empirical aspects of the unlocking of its secrets in Dresden–and the fact that an alchemist played the leading role in solving the riddle of porcelain only enhanced its significance. The art historian Mimi Hellman argues that European porcelain is a quintessential material of the European enlightenment era, embodying on the one hand the confidence and certainty of the time, and on the other, some of the apprehensions and anxieties of 18th century European culture.

Let us now return to the question of how the little blue-and-white tea bowl came into existence in South Carolina in the mid-18th century. Part of this object’s story is touched on above in describing its material’s history, but clearly this is only one out of a multitude of stories that could be told about this object.

I find an interesting parallel in the manifold stories of this little tea bowl with the objects I study with my science students. Like the tea bowl, no single description can fully elucidate the role and function of a protein molecule in a cell, or an organism in its environment. It is by the application of multiple lenses and perspectives that we can more fully appreciate the significance and the beauty of the objects that inspire and fascinate us.