That is the image commonly associated with Greek art, but in this section we shall explore that image deeper. First, there are different types of marble, as it can be obtained from different sites and different areas within each site. All these varieties of marble are derived from the sedimentation (a slow geological rock formation process) of calcite limestone, and are fundamentally related in that regard. They differ due to color, texture, weathering, and chemical composition. Yes, marble it not always white - pure white surfaces were actually avoided by the Greek sculptors for they often made it difficult to see the soft modeling (gentle curves) of muscles.
The most common color (going back to the generic image of Greek art) seen in Greek sculpture is a near white; other colors, used primarily when white marble was inaccessible, include Laconia red marble and Egyptian granite marble. Another key factor that sculptors evaluated before they choose a block of marble to carve was the coarseness or fineness of the marble crystals. A fine texture enabled the sculptor to achieve greater detail with his work. But the smaller crystals (of the finer surface) created a duller surface that was more apt to tarnish by the collection of small particles of dirt in crevices between these minute crystals.
The other extreme choice of texture was the sculptor's option for a coarse surface, with larger crystals that showed readily, which imparted a more brilliant surface to the finished work. The next factor considered in "choice" marble is how the stone weathers with time. In general the coarser the texture the less the surface will darken, but other elements are involved in the weathering especially certain chemical constituents with the marble. One notable example of chemical weathering can be seen today in the Parthenon ruins where the once white color of the marble has turned a rust like orange from the small amount of iron in that particular marble. Unfortunately, another form of modern day weathering is darkening, which not only changes the color of the marble, but is actually destroying the ancient works of the Greeks at an amazing rate (geologically).
Acid rain, the infamous result of a modern transportation infrastructure based on the automobile, is the major cause of this darkening. The growth of cities and their use of petroleum fueled cars has only continued to intensify the problem that leaves no marble statue (ones that are left outside) or building (or ruin) unscathed. Nothing made of marble that is kept outside can avoid the wrath of acid rain, which can be easily explained in chemical terms. Marble, as it is composed of calcite limestone, contains the element calcium, which makes it a basic compound (basic, as in the opposite of acidic). Acid rain is formed when water molecules (such as those in rain clouds) absorb one of two types of sulfurous compounds, SO2 or SO, two chemicals that result from the burning of gasoline. When clouds contaminated with these compounds start to rain down on the earth and the surface of marble sculptures, a chemical reaction ensues that is analogous to mixing baking soda and vinegar. This reaction actually eats away some of the marble-- permanently destroying the marble surface. Efforts to reduce the problem of acid rain (it harms wildlife, plants, crops, soil, and water supplies as well) have lead to the development of catalytic converters on cars, which catch some of the dangerous sulfurous compounds before they exit the exhaust pipe. However, the problem is far from being eliminated. Most of the chemical differences between various types of marble are almost imperceptible by ordinary observation, and are only seen through elaborate chemical testing or X-ray analysis. These discrepancies are useful today to scientists who study where the marble was taken from (e.g. the specific site). This kind of information can then be used to trace the origin of sculptural works and attribute them (as the sculptors rarely signed their works) to the rightful artist.
How can a scientific analysis of a sculpture attribute it to a certain sculptor?
Although sculpture is usually determined along a stylistic basis, the exact marble itself can also be the signature a sculptor. The marble itself contributes to creating the artist's style, since certain types of marble offer unique possibilities that a artist will learn to master once becoming accustomed to a specific type of marble. Surprisingly, the three major Greek sculptural periods (Archaic, Classical, and Hellenistic) drew primarily only on four sources for their marble: the three islands of Paros, Naxos, and Thasos, and the site Pentelic of Attica. Other sources were discovered in later periods, including the immense supply in the Cararra Mountains, which was mined during the Roman era. The location of an artist also helped determine the marble he used, because one of the major drawbacks with marble is difficulty in transportation of the heavy stone blocks. Thus, many sculptors selected their marble from the nearest site. If their planned sculpture was sufficiently large, a rough shape (or finished sculpture) would have to be carved first in order to reduce the weight. Sometimes marble was totally inaccessible and the next best medium (which is actually easier to carve) was limestone. Limestone lacks many of marble's most valuable qualities-- primarily the permanence and beautiful white color of marble, characteristics that made marble the "choice" stone for Greek sculptors. Some other medium alternatives included diorite (a hard black rock), terra cotta (a clay which is strengthened by baking), topaz, and emerald (green quartz).
