Basketry is one of the first crafts used by hominids, but it had little use for carrying liquids. Clay became the go-to material for this purpose, and pottery was born. It was predominantly evident in non-nomadic cultures of Neolithic times, as the objects were heavy and too fragile for constant travel. Most early potters used very little decoration in their pottery. It isn't until the 9th century B.C. that glazes came into use.
A glaze is a liquid combination of materials that almost always include some crystalline matter that becomes glassy upon firing. The glaze is applied to an unfired ceramic piece, usually with a brush or sponge, and the object is fired in a kiln. The firing causes the glaze to fuse with the clay, forming a skin. Raw glazes combine natural and synthetic materials for the desired look upon firing. Fritted glazes contain amounts of pre-melted glass.
Early earthenware had little decoration, but as civilizations developed, so did the ornateness of their functional items. Sculpting and painting on pottery was a simple way to make it more aesthetically pleasing and personalized. Ancient Greek vases and jars are clear evidence of this, and some are exquisite. It wasn't until the 9th century B.C., however, that glazes were developed to suit the same purpose. Decorative tiles in ancient Mesopotamia were glazed for looks.
Five centuries after glazes were used for beauty, archaeological evidence appears of another purpose. Before glazes, liquids seeped into the clay and out of the pot. Exterior evaporation kept water cool but didn't work so well for milk, oil or other liquids. Glazes fused with clay create a watertight seal, and this application appears in the 1st century B.C. in the Middle East, where it may have developed first in Egypt, and in China.