Chalk (Red)
“Iron-stained microscopic shells”
Red chalk is a variety of chalk colored by iron oxide impurities, particularly hematite, mixed in with the usual calcium carbonate from ancient marine microorganisms. It has been used as a drawing material for thousands of years and was a favorite medium of Renaissance masters.
calcite (coccolithophore tests), hematite, clay minerals, quartz (minor)
Hunstanton (Norfolk, England), Central Texas (USA), southern France, northern Germany
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Leonardo da Vinci, Michelangelo, and Raphael all used natural red chalk extensively for their preparatory drawings — the medium gave their sketches a warm, lifelike quality.
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Why was natural red chalk preferred over other drawing media by Renaissance artists?
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