Crackle glass is made by blowing molten glass into a small bulb, then treating the surface by dipping it very swiftly into cold water. This cracks the surface of the glass, which can then be reheated and blown larger to melt the sharp edges and widen the crackle effect. Sometimes, another layer of glass is added, and the crackle effect is totally enclosed.
The technique requires great skill, first to avoid completely shattering the glass and then to avoid melting the cracks completely when reheating. It was first developed in Venice in the 16th century, and later in Spain, the Netherlands, and England.
