Glassmaking | The Donor


Glass was discovered by accident during experimentation with glazed ceramics and faience. The term κύανος (kyanos=blue), found on Linear B tablets, probably refers to the dark blue colour of the oldest vessels uncovered in Mesopotamia and Egypt, which were created some 3500 years ago. The terms λίθος χυτή (=cast stone) and ύαλος (hyalos=glass) appears in the epigraphic and literary record from the end of the 5th century BC. The comic author Aristophanes calls glass vessels υάλινα εκπώματα (hyalina ekpomata) in his work Acharnanians. The main manufacturing techniques οf this unique material, developed over centuries of evolution, consist of forming a core, casting and blowing.
Glass ingredients were washed, crushed and placed in kilns, in order for them to acquire a uniform and vitreous texture. Silica (SiO2) constituted the basic component, alkali - soda (Na20) or potash (K20) - lowered the high melting temperatures silica requires and gives fluidity to the mixture, while lime (CaO) stabilises it. The mixture was melted a second time at higher temperatures followed. This produced raw glass, which displays a characteristic greenish blue colour. The glass-maker could colour the glass by adding small quantities of metallic oxides, or remove colour by adding antimony and manganese oxide.
In Greece, the most important centre of glass-making was Rhodes, where excavations have shown that in the 4th century B.C. both glass vessels and raw glass itself were produced, the latter being thought until recently to have been imported.