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Friday, May 17 • 11:00am - 11:30am
(Research & Technical Studies) Normalized Peak Area Distributions with HPLC-DAD-MS as a Tool for Differentiating Madder and Cochineal Lakes in Easel Paintings

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Historically, organic dyestuffs played an important role not only in coloring textiles but also in producing lake pigments for paintings. The dye sources and recipes of organic lakes varied based on the geographical regions and time periods of production. Knowledge of the relative amount of dye marker components in lakes provides important information about the dye sources and even the manufacturing techniques used to prepare the lakes. This paper presents the results of novel research on the relative amount of madder and cochineal dyes in lakes prepared following historical recipes as well as from unknown samples removed from easel paintings using normalized peak area distributions with high performance liquid chromatography coupled with diode array detection and mass spectrometry (HPLC-DAD-MS). Different methods of dye extraction, separation, and quantitation were selected, optimized, and evaluated. Dye extraction using solutions of boron trifluoride, oxalic acid, and hydrochloric acid were compared. The results showed that extraction using a solution of 4% boron trifluoride in methanol is the most suitable. By this method, the bonds between dye molecules and the surrounding organic binding media are broken up effectively, while glycosidic bonds are preserved. In comparison, the other two extraction methods produced unfavorable results. Specifically, oxalic acid solution does not efficiently extract dyes from painting samples, and hydrochloric acid solution changes the structure of dyes during extraction. Peak areas using diode array and mass spectrometer detectors were evaluated. Calculating the area of individual mass-to-charge ratio peaks using a mass spectrometer detector provides a much clearer separation of co-eluting components than detection by diode array detector, which facilitates quantification of the individual dyestuffs. The peak areas of partially-methylated dye molecules were calculated and reproducible and comparable results were obtained. The indications of the normalized peak area distributions obtained on differences in the relative amount of the same dye between samples was clarified. Further tests on reference samples showed that the amount of sample analyzed or the presence of binding media has little influence on the results of peak area distributions. Challenges arose in the application of the above protocol to samples obtained from easel paintings. The small amounts of samples available led to the addition of second-step extraction with hydrochloric acid solution which affected the comparability of results, and some dye components were below limits of detection by the mass spectrometer detector. Optimization of the application of this semi-quantitation protocol to historic samples is ongoing. In conclusion, the first protocol for the relative amount of dye marker components in paintings, to the best of our knowledge, was established. This protocol constitutes a solid foundation for further study on the diverse sources, methods of lake production, and preservation of organic dyes in easel paintings.

Speakers
avatar for Jing Han

Jing Han

Fellow, Getty Conservation Institute
Jing Han works as a professional fellow at the Getty Conservation Institute. Her work mainly involves the characterization of organic materials, especially lacquer and dyes, by high performance liquid chromatography coupled with diode array detection and mass spectrometry (HPLC-DAD-MS... Read More →

Co-Author
BF

Beatriz Fonseca

Intern, Getty Conservation Institute
Bia Fonseca received her degree in Chemistry from Universidade Federal do Rio de Janeiro, where she also studied three years of Fine Arts, piquing her interest in Conservation. During her studies, she went on to specialize in Physical Chemistry. As a chemist, she worked in Brazil... Read More →
avatar for Douglas MacLennan

Douglas MacLennan

Research Lab Associate, Getty Conservation Institute
Douglas MacLennan joined the Technical Studies research laboratory at the Getty Conservation Institute in 2016. His work focuses on the technical examination of works of art in collaboration with both conservators and curators. His research interests include the use of XRF and multispectral... Read More →
avatar for Michael R. Schilling

Michael R. Schilling

Senior Scientist, Yale Institute for the Preservation of Cultural Heritage
Michael Schilling is head of Materials Characterization research at the Getty Conservation Institute, which focuses on development of analytical methods for studying classes of materials used by artists and conservators. He specializes in gas chromatography, mass spectrometry and... Read More →
avatar for Monica Ganio

Monica Ganio

Assistant Scientist, Getty Conservation Institute
Monica Ganio received her PhD in geology from the Katholieke Universiteit Leuven and a MSc and BSc in Science and Technology for Cultural Heritage from the University of Torino. She joined the Getty Conservation Institute in 2015 to work on technical studies originating from the Antiquities... Read More →


Friday May 17, 2019 11:00am - 11:30am
Nehantic/Pequot/Paugussett Rooms Sky Convention Center, Mohegan Sun
  • Track Research & Technical Studies
  • Ticketed Included in Main Registration
  • Authors in Publication Order Jing Han, Beatriz Fonseca, Monica Ganio, Douglas MacLennan, Michael R. Schilling
  • Abstract ID 18819
  • Tags organic dyes,madder and cochineal lakes,easel paintings,normalized peak area distributions,HPLC-DAD-MS,dye extraction

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