Archaeologically, “rock art” is a term applied to any human made marking on a ‘natural’ stone surface. Relief carvings on a temple wall, for example, cannot be included regardless of how primitive they seem as the stone surface has been ‘prepared’ to receive the sculpture and is no longer ‘natural.’
Rock art is divided into three forms. The first type is petroglyphs which are carved into stone surfaces. Next come pictographs which are rock paintings, some of the most famous of which are found in caves in France. And last is petroforms created by arranging or piling natural stone such as the Nazca Lines in Peru. Petroglyphs and pictographs are again divided into two groups. First is the parietal group, meaning the paintings or carvings are ‘sheltered’ on the walls of a relatively shallow cave or deep in a cavern. The open air group is of course, outside.
Petroglyphs are made through removal of rock surface, including scratching, carving, incising and sculpting. Petroglyphs remove the patina from the rock surface and expose the contrasting lighter colored rock interior. ‘Negative’ images, which are produced by removing the patina surrounding the intended design, are also found. Sometimes petroglyphs are accentuated by additional painting. The amount of repatination on the newly exposed rock surface is indicative for relative dating. Some of the oldest petroglyphs are the same color as the surrounding rock.
Pictography is the application of pigments mostly using mineral pigments such as manganese, malachite, gypsum, clays and various oxides. The simplest pictographs are wet clay finger drawings and charcoal drawings. However, in other locations exceedingly fine line drawing is evidence of the production of excellent brushes. The most common rock art theme around the world is the human hand. A technique used since the Neolithic is spraying around a hand, resulting in a negative image. The more common positive print was often made with pigment applied to the hand and transferred directly to the rock face.
Rock art is found around the world with the oldest so far being in Australia. In the Western World alone there are so many locations where rock art may be found that few people are more than a few hours drive from somewhere where there is some. In the United States, however, most rock art is found in the West and Southwest with good examples at Chaco Canyon, and other sites in Southern and Eastern California. In the north of England in the United Kingdom, one may spot an array of mysterious symbols carved into the rock surfaces.
Minnesota State University has provided a useful online resource about rock art with images, definitions and more. Not only that, but former Google Answers researcher Toby Lee Spiegel has also assembled an impressive array of resources.
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