Hourglasses & Sandglasses
Medieval Science, Technology, and Medicine: An Encyclopedia

The presence of an hourglass (or, to use the UK term, “sandglass”) in artwork from the late Middle Ages and Renaissance is often a symbol of the passage of time, and mortality; a sort of shorthand memento mori. The V&A's website describes their uses and manufacture:

Sandglasses were used in various situations: in churches, typically to time the sermon; on ships to time the length of the watches; in the kitchens of wealthy households, probably to help judge cooking times. They are often illustrated in scholars' studies where they served meditation, or simply helped judge the time of day.

Sandglasses in this period were constructed from two matching glass ampoules sealed (often with wax or pitch) and bound with fabric at the joint. The 'sand' was usually a material less sensitive to moisture such as powdered metal, rock or eggshell.

For more links on timekeeping, click here. See also Robert MacPherson's Pinterest page on hourglasses.