Dating techniques

There are several possible reasons why a scientific study of an art work may be desirable. An obvious one is in cases where the authenticity of an object is doubted on styHstic grounds, but no unanimous opinion exists. The scientist can identify the materials, analy2e the chemical composition, and then investigate whether these correspond to what has been found in comparable objects of unquestioned provenance. If the sources for the materials can be characterized, eg, through trace element composition or stmcture, it may be possible to determine whether the sources involved in the procurement of the materials for comparable objects with known provenance are the same. Comparative examination of the technological processes involved in the manufacture allows for conclusions as to whether the object was made using techniques actually available to the people who supposedly created it. Additionally, dating techniques may lead to the estabUshment of the date of manufacture. 

Dating. The useflilness of dating techniques in the study of art objects, either for authentication purposes or in the evaluation of their historical context, is self evident (41,42). 

Nuclear testing has increased the amount of carbon-14 in the air, and sensitive radiocarbon dating techniques take this increase into account. 

Uranium-series dating is by far the most widely-used dating technique applied to speleothems, and is only applicable to material that is currently in a state of disequilibrium. Given the rates of ingrowth of daughter isotopes of Pa and °Th, conditions of uranium-series disequilibrium in systems which have remained isotopically-closed are generally restricted to materials < 500 ka... 

Combined and dating techniques yield concordant results. 

Standard dating techniques can only be applied usefully to material... 

This volume explains what the image on the Turin shroud actually is and shows step-by-step how it was created. It proves beyond resonable doubt not only who created the image and why, but also whose image appears on the shroud. Using the most up-to-date techniques of computer analysis and imaging this work looks in depth at the shroud s creator, alchemical secrets and the centuries-old conspiracies of silence."... 

A more recently developed technique, known as the accelerator mass spectrometry (AMS) radiocarbon dating technique, based on counting, in a mass spectrometer, the relative amount of radiocarbon to stable carbon isotopes in a sample (see Textbox 10). 

Practical considerations limit the use of the radiocarbon dating technique to a range of 200-50,000 years samples less than 200 years old cannot be called... 

Fluorine Dating. Probably the oldest scientific dating technique is fluorine dating, which, although seldom used today, is discussed here because of its historic interest. Fluorine dating of bone centers on an irreversible process whereby the inorganic component of buried bone is slowly and gradually, transformed into a more stable compound (see Textbox 67) (Camot 1893 Middleton 1845). 

Many more studies have been initiated in attempts to explain the discrepancy between the belief of millions of people and the evidence provided by the radiocarbon dating technique on the age of the shrouds s cloth. Such studies, however, have resulted only in still further studies and a persistent controversy on the real nature of the relic. 

FIGURE 88 Dating methods. Shortly after the discovery of radioactivity, at the beginning of the twentieth century, it was found that the decay of radioactive elements could be used to keep track of time. Many of the dating techniques developed since then are, therefore, based on radioactive decay phenomena, but others, such as the hydration of obsidian, amino acid racemization, and dendrochronology, are based on other physical, chemical, or biological phenomena. 

L and the D/L ratio approaches zero. After the death of the living organism, proteins start to spontaneously break down. An inter-conversion of the amino acids occurs from one chiral form (L) to a mixture of D- and L- forms following protein degradation this process is called amino acid racemisation. The extent of racemisation is measured by the ratio of D/L isomers and increases as a function of time and temperature. The longer the racemisation process continues the closer to 1 the ratio between the D- and L-forms becomes. If the D/L ratio is <1 it may be possible to use it to estimate age. The D/L ratio of aspartic acid and isoleucine are the most widely used for this dating technique [104]. Dates have been obtained as old as 200 000 years. However, it has been used mainly to date samples in the 5000 100 000 year range. Recent studies [ 105] mention an estimation of the method accuracy to be around 20%. 

Considering all the above factors for amino acid racemisation rates, this technique cannot be used as an absolute dating technique. To overcome the problem of uncertainty, the amino acid racemisation method must be calibrated against other more reliable techniques. 

With respect to interpretation, the existence of alternative dating techniques has made clear the necessity for and the difficulty of this step. That is, nature seldom provides ideal dating systems with fixed injection rates, negligible losses, and constant temperature. As a result, simple dates based upon observed isotopic ratios and nuclear half-lives, for example, frequently require cautious interpretation before they can serve as accurate... 

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