Re: ¿Crees en la evolucion?
Patination
Patination is a technique involving the measuring of the patina on an artifact. The patina is the outermost surface of the artifact that differs in color, texture, luster or composition from the rest of the artifact. This difference is the result of chemical, physical or biological change in response to the surrounding soil and environmental condition. Although it is not an actual dating technique, patination is used when multiple artifacts of the same type are found in the same area and under the same conditions. The use of this technique is to determine the age of the artifacts, relative to the others, by comparing the thickness of the patina on them. There are many variables that have to be calculated, and this makes dating lithics from patina formations a relative dating technique.
An example of patination would be a flint artifact buried in some type of soil or sediment that causes its surface to be chemically altered and become white, yellow or brown. Another example would be the green crust that forms on bronze. However, over an extended period of time, stone goes through weathering processes. In 1960 (Goodwin, A.J.H) five types of patination were recognized. The first was bleaching, which is caused by the leaching out silica and replacement of it with lime salts. The second is induration of exposed surfaces, which is caused by the leaching out of soluble silica and redeposition of it at the surface forming a substance called silcrete. The third is limonite penetration and staining which involves limonite clays and salts in the soil being absorbed by stone artifacts. Te fourth is desert varnish which is the condition of extreme dryness and intense solar radiation affecting artifacts. Finally, is the formation of a crust, caused by leaching out iron salts and redeposition at the surface.
Glass objects, as well, go through weathering processes, including a patination. When glass is buried or submerged in water, it undergoes a surface alteration. Thin microscopic bands or layers are formed. Some studies have suggested that the bands form annually. These layers or bands can be counted, almost like dendrochronology, and an age can be calculated.
Patination dating is most useful to confirm stratigraphy. With a site that has several layers of civilizations and a large series of objects from each layer, it is possible to observe obvious differences in the amounts of patina. With this knowledge the layer may be determined from the earliest to the latest civilization.
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