creation

drinking-glass rims

The various types of drinking rim can be used as indicators when dating glass, particularly industrially produced glass.

Traditional technique

To achieve a suitable rim, a small amount of extra glass was left at the top of the drinking bowl (known as a ‘cap’) whilst blowing the glass into the mould. After the annealing process, the cap was scored around the top with a diamond-point tool, allowing it to be detached by heating it on a rotating wheel. The rim could then be finished by grinding, sanding and polishing. To create a smooth rim, the glasses were placed in a carousel and flame polished, allowing the glass to melt slightly under heat. This technique is still used for higher-end wine glasses. Some consider the slightly sharper rim the only correct one for properly appreciating wine.

Modern technique

In the 1950s, a method was developed for separating the top of the bowl from the blowpipe by heating it at a specific point with a ring burner, allowing the bowl and cap to be pulled apart. This produces a relatively thick and polished rim. This method is now used worldwide for machine-made glass. Although the technique has been refined so that the resulting rim is as small as possible, it can still be recognised by the more rounded rim.