||STATE OF THE ART
Although the preservation of painted figures exposed to the outdoor elements for hundreds of years is amazing they are not by any means indestructible. Obviously the pigments have deteriorated at various rates. It is not unusual to see figures with only the ornaments or other specific parts remaining - the rest, painted with less resistant pigments, are gone. The ancient artists seem to have understood the potential action of weathering erosion. Generally near- vertical surfaces slanting backward so as not to face into the rain or dripping water were chosen as the sites for important productions.
The deterioration of pecked figures is a different matter, more than a surface coating must be removed. Anyone who has observed desert rocks knows that a natural protective coating called desert varnish, covers most exposed surfaces. This is a very thin layer of mineral matter, usually rich in iron or manganese that builds up slowly and grows darker and harder with time. Ancient artists recognized the durability of "varnished" surfaces and made use of it in their work. The contrast of it the initial dark surface and the lighter material exposed by pecking creates an interesting long-lasting effect. Even though the fresh surface in time begins to gather varnish it will never become as dark as its surroundings and the contrast remains as long as the rock itself.
Since a varnished surface is virtually indestructible, so are the figures placed on it. What usually happens is that the rock behind the varnish is destroyed or the hardened outer crust flakes or spalls away taking the art with it. Boulders may be observed in process of destruction from the bottom up and from the inside out. This effect is brought about by the upward seepage of water from the soil below. The same action is seen along cliffs, which are banked with soil from which moisture can be drawn into the rock above. Certainly this is the most destructive process at work to destroy rock art in a purely natural way.