This base is in the form of a spiral cable of glass added near the bottom of the vessel.

In Jerusalem, sometime about 40 B.C., it was discovered that molten glass could be inflated. To make this phenomenon useful and practical, manufacturing processes had to be invented. This occurred during a rapid expansion of the Roman Empire that eventually included the entire Mediterranean Basin and extended to the far eastern coast: present-day Israel. Through an extensive trade of goods and the widespread movement of people and know-how, glassblowing found its way to the Italian peninsula. It took root and developed quickly. Glassblowing spread to become—then, as now—the predominant method of making glass vessels. Learn more at https://romanglassblowing.cmog.org.

The resource is a follow-up to Gudenrath's popular Techniques of Renaissance Venetian Glassworking (https://renvenetian.cmog.org) and Technique of Renaissance Venetian-Style Glassworking (https://renvenetianstyle.cmog.org/)