Many items of ancient glassware were designed for tableware use, in particular for carrying and serving water and wine at banquets. Jugs, like this example, were one of the most frequently used containers, and existed in different dimensions and shapes.
The variety of shapes and sizes seen in ancient glassware was achieved through the technique of glassblowing, which by the 1stcentury AD had revolutionised the art of glassmaking. It allowed for easier manipulation of the glass, but also for a quicker paced production, as the hot glass would be blown into a mould and then removed whilst still hot so that the glass maker could still work on it. The ribbing pattern at the bottom of the jug was crafted with this technique. Different minerals were added to create a variety of colours; the yellow tint seen in this piece would have been created by adding lead and changing the oxygen levels. The iridescence on ancient Roman glass was unintentional, and was caused by weathering on its surface. The extent to which a glass object weathers depends mainly on the burial conditions; however, the humidity, heat, and type of soil in which the glass was buried also all affect its preservation.
The iridescence which forms on glass is caused by weathering on the surface of the vessel. How much iridescence is affected by a number of factors, including the humidity and type of soil and to an extent, the composition of the glass itself. Thin layers of weathered glass accumulate and then disperse, sometimes by flaking off, and display a refraction of light.
To find out more about Roman glass please see our relevant blog post: Collecting Roman Glass.
