How to determine the age of a drinking glass

Antiques fairs can seem like a mystery to amateur collectors. In her book Antiques Investigator, expert Judith Miller plays detective, answering the questions you’ve always had about what’s worth buying.

Readers asked: Some glass looks like it was made yesterday—what’s the trick for checking age?

Bowl shape
Check the shape of the bowl of a drinking glass as that can help to date it. (Although remember that every shape has been reproduced later—it is only one clue.) Most early 18th-century bowl shapes were either conical or funnel. By the mid-18th century, there were also bell, thistle and trumpet shapes. Most plain stem glasses have drawn trumpet bowls.

The colour
Much can be deduced from slight variations in the colour of the glass. Even if it is clear, it may have a tinge of grey, green, or amber. If the glass is slightly smoky in tone and shows “crizzling” (in which the surface of the glass has a network of small cracks), this could indicate 17th-century Anglo-Dutch glass. A slight greenish tinge could indicate early lead glass. Later lead glass has a bluish tinge when viewed under ultraviolet light. Glass that has an amber to brown tinge may well be 20th century.

The feel
Feel and look for any joins to see if the glass has been made in more than one piece. Does the piece have a flat or folded foot—can you feel a ridge at the edge of the foot? Is the base thick or thin? Feel in the centre of the foot—is there a rough area that has been broken off? Or is it smooth? Is the piece light or heavy? If the drinking glass has not been made in sections and then joined, it dates from the 20th century.

Flaws and marks
Look and feel for any imperfections in the glass. Imperfections could be a clue to an early glass. Are there bubbles visible in the metal? This could indicate an early glass, but be aware that most glasses with numerous bubbles date from the 20th century. Most glass that is marked is from the late 19th or 20th century.