Materials used in hourglasses include ordinary river sand, powdered marble, fine particles of silver, tin, copper, and iron, burned lead, ground cinnamon, ground eggshells, and fine emery. Historically, ground eggshells were especially well suited for use at sea, perhaps because they resist moisture, and Venetian sand, a dense mixture of burned tin and lead, enabled the device to run for much longer periods without requiring a correspondingly larger glass.
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