Design & Make

Clay’s Evolution

by Melissa Andersen June 14, 2018
ReadClay’s Evolution

Part of what makes us human is our desire to create, to see in raw materials something grander and imagine what could be when only the unformed exists before us. There is perhaps no greater example of this than clay.

Clay has been used throughout time for a variety of different purposes – writing tablets, building materials, musical instruments, tobacco pipes and even as medicine to sooth an upset stomach – but it is in the form of ceramics that clay is best known.

In Neolithic Middle East and Africa, when hunters and gatherers began to transition away from a nomadic lifestyle, clay was used to waterproof the woven baskets in which these early farmers first carried water for crops. Once the baskets were empty and left out in the hot sun, the clay lining dried and hardened, creating a pot-shaped vessel. It was soon discovered that by firing the clay pots in hot ash they could be made even sturdier, resulting in some of the earliest forms of pottery (and, in the process, inventing the first and most basic kilns). Though crude, these objects were the original prototypes that led to the hand-formed and decorated pottery we know today.

Since the concept of ceramics originated in pre-literate cultures, it’s hard to pinpoint the material’s exact evolution. The kiln, for example, likely developed independently in different regions of the world, beginning with the earliest known remains of a pit-like structure dating back to 21,000 B.C. Early Egyptian drawings depict simple updraft kilns, where clay pieces were fired into pottery then rubbed with a stone to produce a sheen, or coated with another fine layer of clay. Later, to make the pottery non-porous, the Egyptians coated their pieces with a bluish-green glaze comprised of quartz, soda and a mineral containing copper.

It was the ancient Greeks, however, who transformed clay into a material for creating fine works of art. Often depicting stories of daily life – or those of the mythological gods and goddesses – Greek pottery celebrated form and decoration without sacrificing utility. The Greeks are also credited with being the first to add color to their vessels by combining clay with natural ingredients, such as ochre and potash.

While kilns and glazes elevated clay into the realm of art, the potter’s wheel had the greatest impact on the material’s accessibility. Prior to its invention (believed to be around 3,000 B.C.), pottery was formed with a simple coil technique, where the clay was rolled into long threads that were pinched and pressed together. These pieces in progress were placed on mats that the potters could rotate – likely sparking the invention of the slow wheel, a mechanism early potters used to slowly turn their piece as they coiled the clay. Later, the fast wheel, which was charged by kicking or turning with a stick to create a centrifugal force that utilized the heavy mass of the rotating stone wheel, led to the process of ‘throwing’ – when a lump of clay is placed in the center of the wheel and then manipulated as the wheel turns. These developments made the mass production of pottery possible (the advent of electricity increased production speeds exponentially) and were the first steps towards the eventual industrialization of ceramics.

It wasn’t until the late 16th-century, when a trade route through Manila connected countries that had previously been cut off from each other, that ceramic wares travelled beyond their place of origin. As the different pottery cultures of Mexico, China, Europe, and others exchanged tools and techniques, a collective knowledge formed, and the craft of ceramics began to evolve.

Physical Stages of Clay

Formed over long periods of time by the weathering of rocks, clay is a fine-grained natural material comprised of one or several different minerals and organic matter. It can be found near bodies of water in regions throughout the world and – depending on the soil content – can be a variety of colors, including white, gray, brown and deep orange-red.

Greenware: unfired objects; clay’s most plastic form
Leather-hard: partially dried; slightly pliable
Bone-dry: ready to be bisque-fired; moisture content at, or near, 0%
Bisque: fired in kiln for the first time; color may change
Glaze-fired: final stage in some pottery making; glaze material melts and then adheres to the object

Types of Clay

Clay can be broken into three distinct categories, generally determined by their firing temperatures: stoneware, earthenware and porcelain.

Stoneware derives its name from its stone-like characteristics: a hard, dense surface and dappled color. It’s typically darker, grittier and more textured than other types of pottery, and may even remain unglazed in some areas, contributing to its handmade feel and quality. In addition to its tactile attributes, stoneware further differentiates itself as the only pottery that rings when struck. Due to a high firing temperature (between 2,100-2,372 degrees Fahrenheit), stoneware is completely leak-proof and quite chip-resistant when fired. This, in addition to the fact that it can withstand very high and very low temperatures, makes stoneware an ideal material for industrial ceramics or functional objects like dinnerware or kitchenware.

Earthenware is fired at the lowest temperature of the three types of pottery (from 1300-2120 degrees Fahrenheit). It’s made with the most commonly found clay in nature. Earthenware is soft and chalky when fired, and can easily be scraped with a fingernail. Its delicate quality and inability to withstand temperature extremes make it a poor choice for cookware, but perfect for decorative objects and tile. Planters and steamers are often earthenware since the material retains its porous nature even after it’s fired to maturity; terracotta is perhaps the most easily recognizable example of this application.

Porcelain’s name refers to texture and translucency and is derived from the Italian “porcellana” for a type of shell that reflects this material’s very characteristics: its hardness, translucency, inconceivably high resistance to heat, distinctively deep white color and range of texture from rough to smooth. These qualities make porcelain perfectly suited for utilitarian wares, household objects, and fine art. Kaolin (also known as china clay) is porcelain’s main ingredient and once fired – at up to 2700 degrees Fahrenheit, the highest of all three types of clay – the resulting material is so hard that even the most formidable steel would leave no scratch. The lengthy firing process allows for a complete molecular rearrangement of the paste in a process comparable to the formation of rocks and minerals in the molten core of the Earth.

The evolution of clay – both as a utilitarian and artistic material – has been an integral thread in the tapestry of human history, often reflecting many of our most significant moments and innovations. In recent decades, those working in clay were considered hippies and hobbyists, but Brooklyn artists like Helen Levi, Nicholas Newcombe, and Rachel Howe are among those leading a ceramics revolution by rethinking the way clay can be manipulated, used and adorned. Unlike clay’s earliest days, these latest innovations were born not of necessity to survive, but of necessity to innovate – and it’s that very human trait that will ensure clay’s place in our collective future for thousands more years to come.

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