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APPLICATIONS OF X-RAY DIFFRACTION IN CONSERVATION SCIENCE AND ARCHAEOMETRY

This paper presents case studies that illustrate the usefulness of X-ray diffraction in the field of conservation science and archaeometry. X-ray diffraction was instrumental in discovering new pigments such as a yellow lead silicate sulfate chloride of the ellestadite group found on fresco fragments from an Abbasid structure built in the early eight century A.D. in Jordan; the yellow compound pararealgar (As 4 S 4 ), which was identified for the first time in a painting; and magnesium cobalt arsenate, a violet pigment found in numerous paintings. X-ray diffraction also helped answer questions related to degradation processes: crystals forming on artifacts in a Canadian museum were identified as cyclohexylamine hydrochloride (C6H13N‧HCl). This finding was key in tracing the source of the problem back to vapour phase corrosion inhibitors used in the museum’s steam humidification system. Badly corroded metal fillets on a Boulle clock proved to be made of tin amalgam, which is susceptible to galvanic corrosion, instead of the more stable pewter. X-ray diffraction analysis of multi-layer samples is also discussed in relation with the later case study and with the study of paint samples taken from polychrome elements of the sculpted decor of the Ursulines chapel, Quebec City.