When was the first concrete evidence of the hour glass identified?

Though is may have been used by the Greek and Romans, the first hourglass, or sand clock, is said to have been invented by a French monk called Liutprand in the 8th century AD. However, concrete evidence of this revolutionary new form of clock, which measures time by the descent of sand from one glass bulb to another, first appeared in European ship inventories from the 14th century. Arriving just in time for the “Age of Discovery”, the hourglass was ideal for ocean travel because the bobbing waves didn’t affect its accuracy.

Sand is the most complex of the components of hourglasses. Not all types of sand can be used because the grains may be too angular and may not flow properly through the neck of the hourglass. White quartz sand, the sand found on sparkling white beaches, is attractive but not the best for hourglass-making because it is too angular and does not flow smoothly. Marble dust, other rock dust and rock flour—powder from glass cutting—and round sand grains, like those of river sand, are best for sand clocks.