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X-ray diffractometry (XRD) is used to identify specific crystalline compounds, both mineral and organic, based on their crystal structure. In XRD, a powder made up of small crystals is irradiated with a monochromatic beam of X-rays with the assumption that the orientation of the crystallite is random. The beam is diffracted at angles determined by the spacing of the planes in the crystals and the type and arrangement of the atoms. A scanning detector or a CCD device records the diffracted beams as a pattern. The intensity and position of the diffractions are unique to each type of crystalline material. This pattern can be identified, even in complex mixtures, by comparison to reference spectra using a computerized database.
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XRD is used widely in determining the nature of pigments, deterioration and alteration products both for building materials and metal objects, and in general to determine the molecular or crystal composition of crystalline materials.
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In addition, XRD is useful in:
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- identification of corrosion products on metal and pigments and grounds of paintings and polychrome sculpture;
- characterization of minerals in stone, mortars, and earthen materials;
- characterization of gemstones and mineral constituents from rock art sites.
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Chiari, G., A. Giordano, G. Menges, "Non destructive X-ray diffraction analyses of unprepared samples". Science and technology for Cultural Heritage., 5(1) (1996): 21-36.
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Chiari, G., R. Giustetto, G. Ricchiardi, "Crystal structure refinement of palygorskite and Maya Blue from molecular modeling and powder synchrotron diffraction". European Journal of Mineralogy, 15 (2003): 21-33.
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Doehne, Eric, Stefan Simon, Urs Mueller, David Carson, and Alice Ormsbee, "Characterization of carved rhyolite tuff—The Hieroglyphic Stairway of Copán, Honduras," Restoration of Buildings and Monuments, 11 (2005): 247-254.
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Last updated: April 2006
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