Examination of pigments on Thai manuscripts: the first identification of copper citrate

Eremin, Katherine, Stenger, Jens, Huang, Jo-Fan, Aspuru-Guzik, Alan, Betley, Theodore, Vogt, Leslie, Kassal, Ivan, Speakman, Scott and Khandekar, Narayan (2008) Examination of pigments on Thai manuscripts: the first identification of copper citrate. Journal of Raman Spectroscopy, 39 8: 1057-1065. doi:10.1002/jrs.1985

Author Eremin, Katherine
Stenger, Jens
Huang, Jo-Fan
Aspuru-Guzik, Alan
Betley, Theodore
Vogt, Leslie
Kassal, Ivan
Speakman, Scott
Khandekar, Narayan
Title Examination of pigments on Thai manuscripts: the first identification of copper citrate
Journal name Journal of Raman Spectroscopy   Check publisher's open access policy
ISSN 0377-0486
Publication date 2008-08
Year available 2008
Sub-type Article (original research)
DOI 10.1002/jrs.1985
Open Access Status
Volume 39
Issue 8
Start page 1057
End page 1065
Total pages 9
Place of publication West Sussex United Kingdom
Publisher John Wiley & Sons
Language eng
Formatted abstract
Samples from Thai manuscripts dated to the 18th to 20th century were analyzed by Raman spectroscopy and Fourier-transform infrared spectroscopy (FTIR) to determine the pigments used. This suggested a change in palette from the 18th to 20th century, with use of imported pigments in the later manuscripts. In the 18th century, the main green used was an organic copper salt, which was replaced by emerald green and mixtures of Prussian blue with gamboge, chrome yellow and zinc yellow (zinc potassium chromate). Chrome yellow was used in addition to gamboge in one later 19th century manuscript. Similarly, indigo in the 18th century manuscripts was replaced by Prussian blue and then synthetic ultramarine in the 19th century manuscripts.

Lead white was the main white pigment in all but one manuscript, which contained huntite, a magnesium calcium carbonate. Huntite also occurred in mixtures with other pigments in two other manuscripts. In all the works studied, red lead, vermilion and red earth were used for red, orange and pink shades and red earth in brown areas.

The organic copper salt used in the 18th century gave good FTIR spectra but could not initially be matched with any published compound. X-ray diffraction (XRD) suggested this was a copper citrate phase, and examination of the literature showed that the FTIR spectra matched those published for a hydrated copper citrate. Raman spectra were obtained from this organic copper salt, which showed close agreement with those obtained from synthetic copper citrate. Copper citrate has not been identified previously as an artist's material, although its use has been postulated on the basis of historical texts. Minor copper formate and/or copper chloride were also identified by XRD and scanning electron microscopy (SEM) in some green samples containing copper citrate.
Keyword Thai manuscripts
Copper citrate
Art works
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Non-UQ

Document type: Journal Article
Sub-type: Article (original research)
Collection: School of Mathematics and Physics
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Citation counts: TR Web of Science Citation Count  Cited 15 times in Thomson Reuters Web of Science Article | Citations
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