A study on characterization of molybdate orange using elemental, vibrational and optical techniques

• Main Author: Paray, Jenibel N.
• Format: text
• Language: English
• Published: Animo Repository 2017
• Subjects: Molybdates; Pigments; Coloring matter
• Online Access: https://animorepository.dlsu.edu.ph/etd_masteral/5769
• Institution: De La Salle University

Molybdate orange [C.I. 77605, PR104, PbCrO4/PbMoO4/PbSO4] is a common modern industrial pigment, however its use by artists is not well documented and almost no identifications of the colorant in artworks have been reported. A brief history of this solid solution lead-based pigment and its relevant chemistry is given along with analytical data for identifying it in works of art using XRF, SEM-EDS, Raman, and FTIR microspectroscopies. The reported lightfastness performance for this pigment varies in the literature and from manufacturers. The Raman and FTIR analysis of the pigments showed that some pigments contain a synthetic organic pigment (SOP). Perhaps surprisingly, the microfading results indicated that some colors containing SOP additives showed better lightfastness over those that did not. Objective measurements of the colorfastness of 2 modern, 5 historic, and 3 in-house synthesized samples of the pigment are reported, both the neat powders and in relevant binding media using a microfade tester (MFT). Poor lightfastness (Blue Wool 3 equivalency) was observed in some samples. The poorer performance in some samples could possibly be linked to the lack of an encapsulation layer on the pigment particles or to color change induced by the binder. The recent discoveries of molybdate orange in three modern artworks at the Indianapolis Museum of Art suggest that the colorant may be far more prevalent than what is suggested by the conservation literature.