Every fired pot quietly records Earth's magnetic field at the moment of firing
When ancient potters baked clay, iron grains inside locked in the direction of Earth's magnetic field at that instant. Archaeologists read that signal today, along with the chemical fingerprints of the clay and a glow test for the last firing, making broken pots among the most talkative objects humans ever left behind.
Pottery is older than farming. Fired clay figures such as the Venus of Dolní Věstonice in the Czech Republic date to between 29,000 and 25,000 BC, and the oldest known vessels, from Jiangxi in China, to about 18,000 BC. Early pottery also turns up in the Russian Far East around 14,000 BC, in Jōmon Japan by 10,500 BC and in Sub-Saharan Africa by 9,400 BC. The first pots were shaped by hand, left plain and baked in open bonfires or pits.
The basic recipe has not changed: shape clay, then heat it to between 600 and 1,400 degrees Celsius so that permanent chemical changes make it hard. Temperature sorts the three classic families. Earthenware, fired low, stays porous and needed glaze before it could hold liquids well; reddish kinds are called terracotta. Stoneware, fired around 1,100 to 1,200 degrees, is tough and watertight. The Chinese mastered it early, while European kilns could not manage it until the late Middle Ages, and it remained a German speciality until the Renaissance. Porcelain needs higher heat still.
Because pottery survives when wood, cloth and food rot away, its fragments are archaeology's workhorse. Styles change over time, so sherds build chronologies for peoples who left no writing. Neutron activation reveals which clay bed a pot came from, tracing trade. Thermoluminescence estimates when it was last fired. Studying the full chain of production, from clay selection to decoration, can show which communities were in contact.
Cooks have their own reasons to love it. Clay holds and spreads heat evenly. A porous earthenware tagine soaks up moisture and releases it as steam, softening food, while dense stoneware will not react with acidic ingredients. Modern ceramic cookware uses clay bodies engineered to expand little when heated, so the pot does not crack.
Source: Pottery
