EARLY PYROTECHNOLOGY. The process of smelting copper seems to have evolved after thousands of years of experimentation with fire. During the Pre-Pottery Neolithic period (8300–5500 B.C.E.), people began to create lime by burning crushed limestone. The lime was then used to produce plaster, with which they coated building surfaces and the skulls of the deceased that were then buried under the floors of their homes. British archaeologist John Garstang discovered this 8,000-year-old plastered skull with painted features and inlaid shells for eyes at Jericho in the 1930s. It may have been used in ancestor worship or to ward off evil.