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absorption
CATEGORY: artifact
DEFINITION: The process by which a liquid is drawn into and fills the pores of a permeable, porous body
atomic absorption spectrometry
SYNONYMS OR RELATED TERMS: AAS
CATEGORY: technique
DEFINITION: A method of analysis used to determine the chemical composition of metal artifacts - especially copper - and non-metallic substances such as flint. It measures energy in the form of visible light waves and is capable of measuring up to 40 different elements with an error rate of around 1 percent. It is not a completely nondestructive technique, since a small sample must be removed from the artifact (between 10 mg. and 1 g., depending on the concentration of the elements). The sample is first dissolved and then atomized in a flame. A beam of light, of carefully controlled wavelength, is shone through the flame to a detector on the other side. The light takes a defined wavelength corresponding to the emission wavelength of the chosen element. The atoms of that element in the sample therefore absorbs a proportion of the light, measured with a photomultiplier, and a comparison of the intensity of the light with that which has not gone through the sample shows the extent of the absorption, thus providing an estimate of the amount of the chosen element in the specimen. One of the method's drawbacks is that a separate measurement (and a different hollow cathode lamp) is necessary for each element, so that analysis for a large number of elements is time-consuming. There are also problems of contamination with the high dilutions necessary for elements present in high concentrations, so that the method is used for the analysis of minor elements and trace elements rather than for major elements. The results are generally more accurate than those obtained using optical emission spectrometry and the technique's use will probably increase, especially for the identification of sources of metal ores through the recognition and quantification of the trace elements.
infrared absorption spectrometry
SYNONYMS OR RELATED TERMS: infra-red absorption spectrometry
CATEGORY: technique
DEFINITION: A technique used to identify mineral and chemical composition artifacts, either to determine their nature or for identification of their source. A small sample is taken from the object and is ground finely before being subjected to infrared radiation. Constituent atoms in the specimen vibrate at characteristic frequencies; if the frequency is the same as that of the radiation, the radiation will be absorbed, while if frequencies do not match, the radiation will pass through the sample. A measurement of the amount of absorption at each wavelength leads to the identification of the minerals and chemical compounds present. Though the method can be used for both inorganic and organic materials, it tends to be used alongside X-ray diffraction for inorganic substances, where it is more sensitive to poorly crystallized minerals. It is most useful for organic materials such as amber, as the organic compounds in the amber absorb different wavelengths of infrared radiation passed through them.

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