From the History of Glass: Casting or Blowing?

Glass molded by ancient Roman craftsmen was found during excavations in the Western European colonies of Rome, as well as in the East right up to the Black Sea coast. After the collapse of the Roman Empire, this craft fell into disrepair and the mode of production was forgotten and never resumed. A new window glass manufacturing method was developed several centuries later, i.e. in the Middle Ages.

First Window Pane

 This method was fundamentally different from the ancient Roman one since glass was obtained not by casting, but by blowing. Initially, a ball was blown, which by rolling on a tile and swinging in the air was turned into a semblance of a large ampoule. After cutting off the upper and lower parts, a cylinder was obtained. The latter was cut along with a solid mineral and, on a red-hot clay plate, was smoothed into a sheet with a wooden smoothing board. The glass turned out to be rather thin, although small in size. The side adjacent to the plate during smoothing also turned out to be rough, which means that the glass was again opaque, as well as the cast one.

Glassblower at His Work

On the territory of the ancient Slavic state, archaeologists repeatedly found fragments of glass circles with a diameter of 200 - 250 mm with well-fixed edges. Scientists agree that these glass circles served for glazing the windows of large public buildings, such as the church of Kyiv Sofia and other churches of pre-Mongol Russia. It is believed that the method of their production was as follows. A vessel resembling a cone-shaped carafe was blown in shape. The bottom of this “decanter” was cut off and the edge was wrapped.