[B._Beckhoff,_et_al.]_Handbook_of_Practical_X-Ray_(b-ok.org).pdf

Nr a 137 the coloration was likely to have been

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) Kupferstichkabinett Berlin (Inv.-Nr. A 137). The coloration was likely to have been created in the sixteenth century, containing azurite, malachite, lead white, cinnabar, ochre, minium, gold ink, and calcite. ( b ) Kupferstichkabinett Berlin (Inv.-Nr. Am 551). The coloration was added in the nineteenth century, con- taining zinc white and chrome green
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692 O. Hahn et al manufacturing of particular pigments. The analysis of special compounds (e.g., gypsum, calcite, or particular salts) which were used as substrate or mordant refers to organic dyes and pigments. Varnishes and binding media consist in general of organic compounds and thereby predominantly of light elements (C, H, O, N, S, P), which give only modest fluorescent signals. Although XRF investigations on polychrome objects especially of larger dimension are usually done non-destructively with open spectrometer set-ups, TXRF is also applicable: Microsamples can be prepared by rubbing a dry cotton–wood bud, a so-called Q-tip, over the painted surface [577]. However, this method does not apply for paintings covered with a varnish. Some difficulties may affect the identification of pigments with XRF. Occ- asionally components which differ only by the mass fraction of some con- stituent elements can form the same pigment (e.g., lead–tin yellow (type I/II) see Table 7.20). Others may also have different crystallographic phases, e.g., titanium oxide, which can appear as either anatase (produced since 1920) or rutile (since 1938). Further difficulty occurs for a couple of pigments, which share colour and characteristic elements but only differ in the occurrence of light elements (C, H, O) whose detection or attribution is not realizable in air (e.g., green pigments such as malachite and verdigris). In multiple layer systems it is generally possible to distinguish information coming from differ- ent layers by means of characteristic ratios of the K to L and L α to L β lines, respectively. If one pigment occurs several times in different paint layers, it is not possible to assign clearly the experimental results, except when using the newly established method based on a confocal 3D micro-XRF set-up. This method was first applied to the non-destructive study of paint layers of Indian Mughal miniature paintings [573]. However, the identification of pigments in paintings [578] and inks in man- uscripts [579, 580] is successful in many cases and the method also allows the determination of the mixing ratios of pigments. By means of adequate quan- tification procedures taking into account inhomogeneous ink paper layer sys- tems, it is possible to discriminate between different historical iron gall inks in manuscripts and compositions [581]. Metals and Archaeometallurgical Samples XRF analyses of ancient metals seek to increase the knowledge of the exact nature of the raw material used, of technological features, of its fabrication as a function of the period and region of origin, and of its history of use as well as of corrosion processes. Information on the chemical composition would
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