The potter has complete control over the shape the pot takes by the pressure, how fast he spins the potting wheel, and the moisture and pressure he applies from inside and outside the pot. He can keep the pot short and stout by slowing the wheel decreasing the outside pressure, or by spinning it faster and pulling upward he can grow the pot taller.
The bearing has to be maintained and kept lubricated, and the potter used animal fat to lubricate it.
The bearing was made of stone, and could be replaced to keep the wheel in the best working condition.
Other ways to create pots, even after the potter's wheel, was to coil the pot and shape it entirely by hand, smoothing out the coils and shaping it with just the artist's skills of hand control. Obviously, the wheel was an invention that much improved the process. Although there would have been highly accomplished artists who perfected the art of hand-made pots, or spinning them in low spinning dishes that required very little in the way of tools.
Kiln Firing, Colors, and Glazing
When clay is fired, it becomes hard, and the temperature at which it is fired categorizes it into the different groups of pottery-ware: earthenware; fired at low temperatures, stoneware, fired at higher temperatures; and lusterware, fired at higher temperatures of 1100-1400 degrees Celsius.
Once the pot is shaped on the wheel to the artist's satisfaction, he would have removed the pot from the wheel, and placed it on a shelf to dry. The unfired clay usually was a reddish-orange color -- depending on the oxide composition of the clay. The artisans were so skillful in their abilities, that not only did they produce recipes for clay, but they also distinguished what kind of firing process and oven was necessary to achieve the specific works.
The horno, or Eastern kiln, can be traced back to it Arabic source.
The firing chamber is located above a hearth, separated by perforated floor.
The horno has a higher temperature condition as a result of its design.
"Thus for slowheating operations, the low-temperature tanur (medieval Castilian or Latin athanor, actanor) was used; the next lowest, according to Gerard of Cremona's twelfth-century translation of De aluminibus et salibus attributed to al-Razi, but with obvious Andalusi interpolations, was the furnum panis, the baker's oven; then, the potter's furnace (furnum figuli) and finally the glassmaker's oven (furnum vitrearii or fusionis). The diffusion of certain kinds of eastern kilns may well have been encouraged by the spread of apposite chemical processes."
If the artist served as a manufacturer on a market scale, he would have had the types of ovens necessary to produce the orders received from his patrons. For lusterware, it would have been necessary to have the high temperature oven, and that would most likely have been the horno oven. This oven would have been able to achieve the temperatures necessary to bring forth the desired luster from the glaze over-coating or under-coating.
The glazes were in large part the color producing methods in the lusterware. In lusterware, the art of tin-glazing was developed by Islamic potters who wanted to imitate Chinese porcelain.
"The art of tin glazing, however, spread from the Islamic world to Moorish Spain, Portugal, France, and Italy and on to the Netherlands. It developed into rich traditions of lusterware, multicolored maiolica, and faience, and as the miles and years added distance, tin glazing departed from...
It is the titanium dioxide, however, that allows the glaze the ability to bend light, and is easily found in the sand of the Central Asian Islamic world.
Combining titanium and small amounts of rutile, an iron-rich version of titanium dioxide, look white at room temperature, but when fired to 150 degrees Celsius, looks yellow.
The tin-glazing would have been applied by the artisan as an over-coat, or an under-coat. The layers or thickness of the glaze would have added, or taken away from, the luster effect once fired. Also, the luster effect was created in a "smoky" oven. And the heat, the glaze, and the smoke did not always produce the perfect product. It took skill, acquired only through much experience with the clay, glazes, and firing processes to create the most desirable pieces of lusterware. These tin-glazing techniques yielded a vast wealth of lusterware, which was as desirable to the Chinese and to the Western world as was the Chinese porcelain that inspired the art of tin-glazed pottery.
Bibliography
Grave, Peter, (Andrew S. Fairbairn, Sue O'Connor and Ben Marwick, Eds.) Melting Moments: Modelling archeological high temperature ceramic data, New Directions in Archeological Science (2009), Archeology and Palaeonthropology (University of New England, Armidale, Australia), Chapter 15, 215-232.
Memmi, Isabella Turbani, Pottery production and distribution: the contribution of mineralogical and petrographical methodologies in Italy, Periodico di Mineralogia, 73 (2004), 239-257.
Staubach, Suzanne, Clay: The History and Evolution of Humankind's Relationship with Earth's Most Primal Element (2005). Berkley: Berkley Hardcover Press.
Zaimeche, PhD Salah, Malagwa, Foundation for Science Technology and Civilisation (2005), June, 8.
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