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Natural Coloration
Glass is not naturally colorless. Beach sand
invariably contains black particles of iron oxides scattered through
it. When fired in a usual, oxygen-rich environment (i.e., with the furnace in an
oxidizing state), these impurities give the glass a natural
aquablue to light green tinge. The typical amount of iron in beach
sand is 0.3%: the intensity of the color increases as the amount
of iron increases.
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Juglet 4th century A.D. Ht., 12.3 cm
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