prunt
A small piece of glass fused to the main body of a piece of glasswork and then shaped or pressed, for decoration
prunt: decorative glass blob fused then shaped on the fly
A prunt is a small mass of molten glass applied directly to the surface of a hot glass vessel, then immediately shaped or impressed while still plastic. The glassmaker uses a hand tool, often a puntil or specially designed stamp, to form the prunt into a specific profile before it cools and fuses permanently to the body. The result is a raised decorative element that catches light and adds texture to otherwise smooth surfaces.
Prunts have been used in glassmaking since medieval times, particularly on drinking vessels and pharmaceutical jars. A typical prunt might be 10 to 20 millimetres across and 5 to 10 millimetres proud of the surface. Common shapes include ribs, bulbs, rosettes, and lion masks. The technique requires timing and skill: the prunt must be hot enough to fuse completely but cool enough to hold its impressed form without sagging or deforming under the tool.
The weak point of any prunt is the join between it and the main body. If the base glass and the prunt glass have significantly different thermal expansion rates, stress concentrates at this junction during cooling, leading to cracks or complete detachment. Poor fusion, where the prunt never fully melts into the body, is another common defect. Blown glass vessels are especially prone to prunt loss because the thin walls cool rapidly and the prunt mass can trap heat unevenly.
Prunts appear most often on German Waldglas (forest glass) vessels of the 15th and 16th centuries and on English wine glasses from the 17th century onward. The name likely derives from the German word Prunge or similar, though its exact etymology is disputed. In modern studio and production glasswork, prunts remain a labour intensive decoration, which is why they are now uncommon outside specialist makers and heritage reproduction.
Related decorative techniques include applied threading (thin trails of glass wound around the body) and rigaree (impressed or tooled trails). Unlike those methods, prunts create a three dimensional lump that must be formed in a single working session, making them distinct from post annealing surface treatments.