Until the plastics age of the twentieth century, and many would possibly say into and beyond it, glass was once the remaining cloth for making containers. It resists all substances—except hydrofluoric acid. It exists in nature in the shape of obsidian, a volcanic rock of which man-made artefacts have been found, such as arrowheads. The earliest artifical glass is dated at about 4000 BC in Egypt, as a simple glaze on beads. Not till about the seventh century BC are Assyrian examples of small decorated jugs found, made by using casting the glass round a clay core which ought to then be scraped out. A awesome advance used to be the blowing iron, allowing larger and thinner vessels to be made. This originated in the first century underneath the Romans.
