Wednesday, October 18, 2006


Jasper exhibits various colors, but chiefly brick red to brownish red. It owes its color to admixed hematite, but when it occurs with clay admixed, the color is a yellowish white or gray, or with goethite, a brown or yellow. Often jasper is multi-colored. In ancient writings the term jasper was chiefly applied to translucent and brightly colored stones, particularly chalcedony, but also was applied to the opaque jasper. Jasper was known as the great "rain-bringer" in the fourth century. For thousands of years, black jasper was used to test gold-silver alloys for their gold content. Rubbing the alloys on the stone, called a touchstone, produces a streak the color of which determines the gold content within one part in one hundred. Jasper is one of the gemstones, that used in commesso, also called florentine mosaic. Commesso is a technique of fashioning pictures with thin, cut-to-shape pieces of brightly colored, semiprecious stones, developed in Florence in the late 16th century.



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