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.



The layers in these stones range from translucent to opaque for sardonyx. The stones vary in color, too. They may be white or gray, ranging to many colorful varieties. Sardonyx stones usually contain flat-banded, white and brownish-red bands. Onyx is a gemstone with alternating light and dark bands, which are colored in brown, red, black, white and grey. The name onyx was used by the Romans for a variety of stones including alabaster, chalcedony, and what is now known as onyx marble. Roman soldiers wore sardonyx talismans engraved with heroes such as Hercules or Mars, god of war. They believed that the stone would make the wearer as brave and daring as the figured carved on it. During the Renaissance, sardonyx was believed to bring eloquence upon the wearer and was regarded with great value by public speakers and orators.Cameos are cut from stones, such as onyx, sardonix or agate, where different colors occur in layers.



Royal purple or generic purple is the common layman's idea of purple, but professional artists, following Munsell color system, regard purple as being synonymous with the red-violet color shown at right, in order to clearly distinguish purple from violet and thus have access to a larger palette of colors. This red-violet color, called artist's purple by artists, is the pigment color that would be on the color wheel between pigment violet and pigment magenta.
Artists pigments and colored pencils labeled as purple are colored the red-violet color shown at right.


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