Jacks

What it is

Jacks are two metal arms joined at one end by a spring; the glassworker controls the distance between them.⁠^⁠[3] Wikipedia describes them as shaped “somewhat like large tweezers with two blades”.⁠^⁠[4] The Corning Museum of Glass gives borsella and pucellas as other names for the tool.⁠^⁠[3]

How it’s used

Jacks are used for many jobs while shaping the hot glass, including forming the mouths of open vessels.⁠^⁠[3] The Conciatore lexicon lists the main ones:⁠^⁠[2]

• Necking down: squeezing the glass near the blowpipe with the inside of the blades. On Murano the everyday jacks are borsee da siegar, from the word for “to saw”, after this motion.
• Widening and narrowing the piece.
• Opening hollow pieces with the outside of the blades.
• Modelling the glass by pressing the hollow form straight on or at an angle.

History

Murano’s glass museum describes the borsella as flexible iron tongs used to shape molten glass, made in different forms for different jobs, and calls them, together with the blowpipe, “the glass master’s main and most versatile tool”.⁠^⁠[1]

According to the Conciatore lexicon, the origin of the word is unknown, but goldsmiths used borsela for a spring clamp long before, and the glassmakers probably borrowed it.⁠^⁠[2] Traditionally the jacks were made in two parts soldered together: the blades, forged by hand from iron, and the spring and handle, a flat bar bent by hammering it cold around an anvil, which gave it its spring. Today the blades come from pre-sized steel bar and the backs are often cut by water jet.⁠^⁠[2]

Variations

Blade shape and material vary: the jacks in this archive include standard, round, oval, cup and goblet blades in steel, stainless and bronze. Parchoffi replace the metal blades with wood.⁠^⁠[2]