Glaspropp

Glaspropp refers to a stopper or plug made from glass designed to seal a glass container. Unlike cork or polymer closures, a glaspropp is typically formed from common glass compositions such as soda-lime or borosilicate and is ground or shaped to fit the container neck precisely. The primary purpose is to provide a leak-tight seal with high chemical inertness and heat resistance, suitable for certain laboratory and industrial contexts as well as vintage bottles.

In Swedish and some Nordic usage, glaspropp literally means glass stopper and is used to describe both historical and contemporary closures for bottles, flasks, and vials. The term is sometimes encountered in English-language discussions about antique glassware or specialized laboratory equipment.

History and design: Glass stoppers began to appear in Europe during the late medieval and early modern periods, evolving from crude closures to more precise, ground finishes in the 17th and 18th centuries. A glaspropp is typically cylindrical or slightly tapered, with a flat or rounded top and a ground, finished surface that mates with a corresponding bottle neck. Some designs include a bore or groove to aid sealing or venting, but most rely on a tight mechanical fit and glass-to-glass contact rather than elastic seals.

Manufacture and use: Producing a glaspropp involves glass blowing to form a stock shape, followed by grinding, polishing, and annealing to relieve stress. Today, glass stoppers are most common in specialized laboratory glassware and vintage or specialty bottles where chemical inertness and high-temperature tolerance are required. They are relatively fragile and can be expensive to replace, which limits their widespread use in everyday packaging.