Welcome to the Glass Age

28 products. They readily form glasses because their melts are viscous, and their interlinked atomic components cannot easily re-arrange into regular crystal structures. Their high viscosity also makes shaping into containers, sheets, fibers and tubes possible (see Chapter 13). Glass making, its origins Society has used glassy materials for millennia. Initially these were naturally occurring, particularly obsidian, a rapidly cooled volcanic lava which had failed to crystallize. It was sculpted into arrowheads which could be used to catch food and axe heads which could shape wood. Smaller pieces became jewelry and larger pieces were even polished to make mirrors. As human society developed and learned how to control fire, the skills of the metallurgist were developed giving the Bronze Age. Somewhere someone discovered that the same heat sources could melt sand if a flux was present. The early fluxes used particularly by the more advanced societies in the Middle East were white salts rich in sodium and potassium, although they didn’t know that! Such materials are found on the shores of dried-up lakes (Wadis) in the Nile basin for example and in the ashes from burning plants. These were actively traded because of their value in medicine, as detergents and in dyeing. The metallurgists and glass makers would also no doubt have shared their skills in furnace technology. Over the centuries, the raw materials used evolved. Purification/beneficiation processes improved, compositions changed to introduce color, increase chemical durability, and create products with optimized characteristics over a wider range of properties. Archaeologists now use compositional information (elements and their isotopes) to uncover ancient trade routes, to identify the sites of glass works, the source of their raw materials, and the distribution of the finished products. Figure 2.1. Egyptian container. Source: Turner Museum of Glass (Simon Bruntnell).