The Science of clay.

What is clay? Where did it come from? What is a glaze? How is it different from paint? What is a kiln? What does it mean to "fire" a clay object? What kind of matter is clay? Is it a solid, liquid, or gas? What chemical changes take place during firing?

Do your students ever ask any of these questions? Their natural curiosity provides a rich opportunity for you to make meaningful scientific connections between art and ceramics that will enhance their understanding of both natural forces and scientific aspects at work in the creation of clay artworks. Students are highly motivated by both experiments in science and by creating their own art with the wonderful malleable mud we call clay. Scientific areas of study related to clay include geology, chemistry, archaeology, biology, and physics.

Geology

The earth was once a mass of molten material. As it cooled, heavier materials settled into distinct layers. Igneous rock, formed by heat, makes up the surface layer. Weathering breaks up rocks and erosion caused by water, ice, and wind breaks them down and carries away the pieces to deposit them elsewhere. Rocks that decompose into clay at the site of their formation are called primary clays and they are fairly pure clay. Rocks and mud that have been eroded and deposited by water, wind, or ice to a different location are called secondary clays. These clays acquire impurities in the form of other minerals so they become darker and coarser. It takes a mixture of primary and secondary clays to make a good clay body for ceramics.

Chemistry

Clay is composed of about 70% silica, 15% alumina, other minerals, and water. Silica hardens the clay in firing and alumina slows the firing enough to prevent cracking, breaking, and exploding in the firing process. The minerals that are found in or added to clay bodies have different characteristics that influence color, strength, and heat tolerance in clay bodies. Certain minerals have predictable colors when they are fired, and they are referred to as colorants. For example, cobalt produces blue, copper makes green, and iron gives brown.

A glaze is essentially a thin layer of clay applied on the surface of a clay body and hardened to glass through the firing process. Glazes actually become a part of the pot when fired, unlike paints that just attach to the surface. A glazed pot is stronger than unglazed ware, nonporous, and easier to clean. Artists have made an art form of glazing because it offers such variety and beauty to ceramics.

Biology

Bacterial growth is important in the improving of plasticity or malleability in a clay body. When clay is commercially processed for use in ceramics, it is aged by the addition of bacteria to make it more plastic. Clay found in nature contains bacteria mixed into the clay by the addition of impurities through the decay of plants and animals in riverbeds. This knowledge can help students understand why the clay they find along streams and rivers and in their flower beds is more difficult to use than commercially processed clay.

Archaeology

The study of human history through the forms and styles of clay artifacts and shards has long been of interest to archaeologists and to artists and students of art. Much of what we know about ancient cultures is derived from their ceramic art processes and pottery shards. Since the time of the first potter who discovered that clay hardened in a fire, pottery has been used for both practical and ceremonial purposes. Even before people wove clothing to wear, they made objects from clay.

Fired clay is an extremely durable material. Hand-molded clay figurines dating to 26,000 BC have been found in Europe. Clay vessels from the Jomon culture in Japan have been dated to around 10,500 BC. Clay was used to make tablets for writing by the ancient Babylonians and ancient tiles and pots from many cultures are decorated with stories of heroes and villains. From pottery, we learn something of our ancestor's lives, dreams, and adventures. Pottery provides a focus through which to teach about cultures around the world and the history of their use of ceramics.

Physics

Firing clay uses energy in the form of heat to change the form of matter to make it permanently hard and glass-like or vitreous.

Vocabulary

clay: a compond of decomposed and altered feldspathic rock consisting of various hydrated silicates of aluminum along with non-plastics, such as quartz, and organic matter.

pottery/ceramics: objects shaped from moist clay and hardened by heat.

matter: anything that has mass and occupies space; physical properties of matter are shape, size, solid, liquid, or gas.

glaze: a glass-like coating fusion bonded to a ceramic surface by heat.

kiln: a high temperature furnace used to fire pottery.

firing: to heat clay at high temperatures in a kiln.

vitrification: to fire to the temperature at which a clay or glaze attains its mature, hard, glass-like quality.

A fossil is a remnant, impression, or trace of an organism of past geologic ages that has been preserved in the earth's crust. ([dagger]) It could be any remains, trace, or imprint of an ancient plant or animal, usually molded by clay that hardened around it as the organic object it enclosed decomposed over time. What kind of "fossils" can your students create using clay?

Hands-on Experimentation

* Students can experiment with making a clay body by digging, drying, and cleaning found clay by sifting it through a window screen and then mixing in water. They can form one pinch pot from this natural clay and another from commercially processed clay to compare and contrast the two. Mud from a riverbed, stream or other body of water will do. Students can then use a common colorant like red iron oxide to draw on the ceramic pieces before applying glaze and firing to observe the interaction between colorant and glaze.

* Students can replicate prehistoric clay traditions by making coil pots.

* Students can make their own "fossils" using shells, leaves, or even plastic dinosaurs.

NATIONAL STANDARDS

Students describe ways in which the principles and subject matter of other disciplines taught in the school are interrelated with the visual arts.

WEB LINKS

Burnt Earth: The Science of Ceramics, banyan.chatham.edu/pti/ Everyday%20Science/Gaser_02.htm The American Ceramic Society, www.ceramics.org/

References

Fransworth, Warren. Beginning Pottery. New York: Van Nostrand Reinhold Company, 1973.

Nigrosh, Leon I. Claywork: Form and Idea in Ceramic Design, 3rd ed. Worcester, MA: Davis Publications, Inc., 1994.

Tipton, Barbara. Answers to Potters' Questions. Columbus, Ohio: Professional Publications, Inc., 1990.

([dagger]) Merriam-Webster Online Dictionary

Sharon Warwick is national art consultant for Scott Foresman Publishing. [e-mail]