With support from the Chemical Measurement and Imaging program, Profs. Richard Van Duyne and George Schatz of Northwestern University, and Dr. Francesca Casadio of the Art Institute of Chicago, seek to develop new analytical and theoretical methods to determine the molecular structure of natural organic pigments and dyes, both original and deteriorated, used in cultural heritage materials. Targeted aims include ultrahigh sensitivity, high spatial resolution, minimum sample damage, generality, and independence from reference libraries for identification. Both plan-view and cross section molecular mapping capabilities are sought, at multiple spatial scales (micro to macro). Deep near infrared (NIR; 800-1300 nm) excited surface enhanced Raman spectroscopy (SERS) will be developed to study pigments and dyes with minimum fluorescence and minimum damage to precious art works. Advanced theoretical methods will be used for molecular structure identification beyond the limitations of a pigment library. Theory will also be used to predict possible degradation mechanisms of faded colorants and to model optical properties and optimal structures of plasmonic nanoparticles and their assemblies to give maximum SERS sensitivity.
These collaborative studies will have broad impact not only on nanoscale science and technology (including plasmonics/SERS), but from providing opportunities for students and postdocs (including members of underrepresented groups) to appreciate and engage in unique research at the interface between art and science. The work includes outreach to a wide public audience, using both the visual and media appeal of research stories tied to widely recognized paintings and works of art. Finally, the PIs will work with the AIC's Museum Education Department to develop innovative materials and programs that illuminate the myriad connections between exploration in the sciences and interactive experiences with art. Specifically, a one-week intensive summer course for teens (Inquire/Design) will be developed and offered broadly with an emphasis on attracting minority students in Chicago. The broad audience base in terms of general public and teachers/students served through the AIC's Student Program division of the department of Museum Education will exponentially enhance the outreach of this science/art program.
Museums have very few minimally invasive techniques to study organic colorants, which are among the most fragile components in works of art. Identification of pigments is one of the first steps in formulating treatment and exhibition guidelines that rely on solid scientific ground. Our research provides new tools for the study of pigments in original and degraded cultural heritage materials to help conserve and properly exhibit these precious works of art. The project used chemical analysis, nanoparticle-based sensor technology, and theoretical models to develop methods for sensitive and accurate identification of pigments. In one study, a new technique was developed to identify an important historical pigment eosin Y. Many works by Vincent Van Gogh (1853-1890) were painted with the bright pink pigment eosin which now appears completely faded. We were able to detect eosin Y (a light sensitive dye found in Van Gogh paintings) using surface-enhanced Raman spectroscopy (SERS). SERS is a technique that uses nanoparticle substrates as antennas and lasers to excite the nanoparticles. This technique makes it possible to identify a specific colorant with very high sensitivity. The results are comparable to quickly finding a needle in a haystack. In many cases it is difficult to properly identify and interpret the data that is generated using SERS. Thus, we also developed a theoretical model based on time-dependent density functional theory (TDDFT) to confirm identification of this pigment. This enabled the successful detection and identification of minuscule amounts of an artist’s dye with laser illumination at a wavelength which will cause minimal damage. This outcome opens up a new tool that museums can use to identify pigments (such as eosin Y and its degradation products) in severely faded paintings and use it to propose digitally reconstructed artworks to the public that more closely resemble those originally conceived by the artists. In another study, SERS techniques were developed to detect pigments in wool, silk, cotton, and flax fibers, which represent an important part of the natural fibers used to make textiles from antiquity to the present day. We then applied the method to examine six historical textiles from an important collection of Mariano Fortuny (1871-1949) textiles at the Art Institute of Chicago to shed light on Fortuny’s fascinating production techniques. A mixture of cochineal (an insect-derived colorant) and brazilwood (a plant-derived colorant) was detected in some of the historical samples demonstrating, for the first time, simultaneous identification of these colorants used in combination on a very small sample. In addition, the findings give substance to the claim that Fortuny kept using natural dyes at a time when many new and attractive synthetic products became available. This project brought advanced scientific tools to the Museum community. The Art Institute of Chicago also designed, planned, and delivered a 5 day intensive workshop for 15 to 17- year olds called The Art and Science of Color. The students explored paint and color from an artist’s perspective, along with light, color and artists’ materials from a physics and chemistry perspective. The program received extremely positive reviews by the teens who participated. This and other outreach activities from this project have increased various communities’ interest in pursuing further education in the sciences by increasing awareness of both artistic processes and scientific investigation. Overall, in-depth studies such as those described above are rapidly increasing the utility of SERS and TDDFT for analysis of cultural heritage items. The results of this work will have a transformative role in our ability to study and preserve works of art as well as ethnographic and archaeological artifacts and bring about a new level of understanding of the materials used without the need to remove large samples. Dr. Casadio, Professor Van Duyne, and Professor Schatz are extremely excited about the prospects for this work and further augmentation of this powerful analytical tool for cultural heritage analysis.
