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general::
Also, black as coal or pitch. Totally black; also, very dark. For example, The well was black as night, or She had eyes that were black as coal. These similes have survived while others? black as ink, a raven, thunder, hell, the devil, my hat, the minister's coat, the ace of spades? are seldom if ever heard today. Of the current objects of comparison, pitch may be the oldest, so used in Homer's Iliad (c. 850 B.C.), and coal is mentioned in a Saxon manuscript from A.D. 1000. John Milton used black as night in Paradise Lost (1667).
American Heritage Idioms