Petroglyphs and Pictographs
Petroglyphs and Pictographs
In archaeology, petroglyphs and pictographs are terms used to describe forms of rock art. Petroglyph is derived from the Greek words petros (stone) and glyphein (to carve). Pictograph, or pictogram, is a combination of the two words picture and graph, where picture is derived from the Latin word pictus (to paint) and graph is from the Greek word graphos (writing). Petroglyphs have been discovered in parts of Africa, Australia, southwestern North America, the Scandinavian countries, and the Siberia region within Russia and Kazakhstan.
Petroglyph refers to a rock carving or etching, while the term pictograph is commonly applied to a rock painting. Typically, these features are found on the vertical or overhanging surfaces of large boulders and are sometimes associated with nearby settlements. However, they are often found isolated a great distance from living areas. Although both types of rock art can be traced back to early prehistoric times, their occurrence in historic contexts is not uncommon. In fact, many traditional aboriginal cultures in Africa and Australia still practice the art of rock painting.
Origin and manufacture
Some of the oldest known rock art features are pictographs in France and Spain; cave paintings made by the Cro-Magnon culture of early humans have been dated to more than 30,000 years old. Protected from rain and sunlight in deep, underground passages, these features have withstood the ravages of time. Most of these colorful images are of animals such as deer and antelope, and are strikingly detailed and life-like.
When humans migrated into North America some 12,000 years ago, the practice of creating rock art was brought with them. As time progressed and people spread out across the Western Hemisphere so did the use of rock art. Eventually, nearly all of the more than 200 distinct Native American tribes in North America used some form of rock art in ceremony. Interestingly, many of the artistic elements or patterns used in petroglyphs and pictographs are very similar among these many diverse groups.
From historic cultures that continue to create rock art, we have learned that petroglyphs were made by using a hand-held stone as a chisel or hammer to etch designs into boulders.
Pictographs, however, were considerably more complex to make because of the materials required for paint. Red pigments, which generally comprise the most common color found in rock paintings, were made from ground iron oxides obtained from the minerals hematite or magnetite. Talc, gypsum, or lime was used to make white; charcoal or graphite were employed for black; and copper ores were sometimes used for greens and blues.
These minerals were ground into fine powders then mixed with a resin, such as pine pitch. An oil base was sometimes added by grinding certain seeds or extracted from animal fat. Paints were applied either by fingers or with brushes made from the shredded end of a stick, animal fur, or fibrous plant leaves.
Analysis of rock art
There are, generally speaking, two ways to look at rock art: descriptively and comparatively.
In descriptive analyses, information about a prehistoric culture is obtained from the picture motifs that appear in that culture’s art. Such information, which may pertain to social activities, economics, material culture, ideology, and environmental context, may not be available in other types of archaeological evidence. In the absence of other methods, the picture motifs may also provide a basis for dating the site and objects found there.
As a cross-check to conclusions based on identification of picture motifs in prehistoric art, archaeologists also analyze writings about the past that have survived. Another problem with trying to extract information about a culture from the pictorial content of surviving rock art, is that the pictures, as drawn, were cultural interpretations of reality, and not true representations of the culture’s values, beliefs, and so on.
Nevertheless, in some parts of the world, descriptive analyses of rock art have yielded important information about the animals, tools, weapons, economics, and social conditions in vanished cultures.
Comparative analyses are based on selective patterns that show up in the observed distributions of rock art. For example, the geographical distribution of rock art sites may be highly patterned due to such factors as local geology, the way the sites were used, patterns of land use, and belief systems prevalent in the culture.
Dating rock art
A major limitation in rock art studies is that rock art can be difficult to date. The dating techniques currently in use fall into two broad categories: relative dating and absolute dating.
Relative dating techniques include observations of patterns of chemical and physical weathering, evidence that art has been painted over, stylistic patterns, and variations in the spatial patterns of rock art indicating chronological sequences of site occupation.
Absolute dating methods include analyses based on subjects depicted (e.g., representations of extinct animals), one-to-one mappings with datable deposits, dating of stratified deposits associated with the rock art, and the actual dating of the art itself.
Occasionally, it has been possible to date rock art directly by chemically analyzing the organic materials that were used to draw it, for example, charcoal, plant fibers, and protein binders. A major problem with this approach, however, is that the sampling procedure damages the rock art to a certain extent.
Dating technologies include standard radiocarbon dating, cationratio analysis (based on separate rates of leaching for the chemical constituents of desert varnishes), amino acid racemisation (based on the decomposition rates of amino acids), optically stimulated luminescence (based on the length of time that quartz grains have been removed from sunlight), lichenometry (based on lichen growth rates), and micro-erosion analyses (based on weathering patterns).
Current research
Although pictographs and petroglyphs have withstood hundreds, perhaps thousands of years of exposure, modern pollutants and vandalism, coupled with natural elements, have accelerated their destruction. Recently, scientists have used microscopic mineral sampling to measure the types of chemical elements found in pictograph pigments. Additionally, studies have included the use of diversional water-sheds, shelters, and application of protective adhesives to prevent rock art erosion. The continuing study of chemical compositions and rates of panel decay could one day lead to the discovery of a proper means by which to preserve these features indefinitely.
Randall Frost