bullion

A bullion is the rough mark or scar left on a finished glass piece where it was held during manufacture by a punty rod, also called a pontil. This iron rod, typically tipped with a small glob of molten glass, attaches to the piece during shaping and detaches after the main work is complete. The detachment leaves behind a raised bump or crater, depending on how cleanly the glass breaks free from the iron.

In flat glass production, particularly windowpanes and blown vessels, the bullion appears as a circular depression or protrusion on one surface. For windows made by older methods, the bullion often sits at the center of the pane and was ground smooth during finishing. In blown glassware, especially drinking vessels and decorative pieces, the bullion typically marks the base or bottom of the object. On high-quality work, the glassmaker grinds and polishes this area; on utilitarian pieces it may remain visible.

The term bullion also sometimes refers to the punty rod itself in certain regional dialects, though this usage is less common. The size and severity of the bullion depends on the temperature at which the punty is removed and how deliberately the glass is cracked away from the iron. A cold punty detaches more cleanly and leaves a smaller mark than one pulled away while still hot and plastic.

Grinding out the bullion is a secondary operation performed on pieces destined for display or sale at higher grades. A carborundum wheel or felted lap removes the raised material and smooths the cavity. On mass-produced tableware and industrial glass, leaving the bullion unground is standard practice and accepted by end users. In scientific glassware and high-end stemware, however, complete removal and polishing is expected.

The word bullion derives from the same root as the verb 'boil', referring to the bubbling or globular nature of the molten glass mass that forms at the punty's tip. It is distinct from other glass defects such as seeds (trapped bubbles) or stones (inclusions of unfused material), and it is not a flaw in the glass itself but rather an inevitable artifact of the manufacturing process.