Direct Analysis in Real Time – Time of Flight Mass Spectrometry (DART-TOF) was shown to be a viable method of organic dye analysis in the presentation by Cathy Selvius-DeRoo. The beauty of the technique is that it requires only a small fiber sample, and no advanced preparation such as dye extraction, in order to get positive identification for a variety of dyes, both plant and insect based.
The project began with a grant to purchase the equipment. From there, various colorants were tested from a dye sample book, in order to develop the protocol. The sample was put in the ionizing gas airstream (helium) and heated to a temperature of 350 – 500 degrees. The result was fast and accurate identification of several dye classes, such as quinones, tannins and indigoids.
The presenter had a relaxed, personable style and shared some of her tips for success as well as lessons learned, including: better results were achieved with the higher temperature and with the addition of acid hydrolysis, which could be added just prior to putting the sample in the airstream using an eyedropper. The presenter confessed that flavonoids could be difficult to discern because the spectra are very similar for the various components.
After the method proved reliable, the technique was tested on textiles with undocumented dyes. The most satisfying was to substantiate family lore on a Civil War coat. The story was that a mother of a soldier dyed a Union issued coat to resemble a Confederate coat. Analysis revealed that the indigo was overdyed with Walnut (also referred to as Butternut). Cool.
Full disclosure – I signed up for blogging this talk because I’m a bit of a science junkie. I don’t always understand it, and in a small private practice, I certainly don’t have a Mass Spectrometer in the studio, but I appreciate knowing how to solve problems and who to go to for help.
Author: Beth Szuhay
42nd Annual Meeting, Textiles Session, May 29th: A Case Study Using Multi-band and Hyperspectral Imaging for the Identification and Characterization of Materials on Archaeological Andean Painted Textiles by Rebecca Summerour and E. Keats Webb
The paper began by acknowledging a third author who was inadvertently left off the program and abstract booklet, but will appear as a third author in the TSG Postprints. The paper was presented by E. Keats Webb, the digital imaging specialist for the Conservation Institute at the Smithsonian. She showed how by combining a lower resolution spectral camera (Surface Optics Corp SOC710) with a modified DSLR with bandpass filters, the resulting images could be used to identify certain pigments on a painted textile. The project began with four textiles being described as plain weave with color (a limited color palette of browns and blue/blacks) delivered in a paste form without an organic binder, the color remaining on one side – this is important, keep this in the back of your thoughts as you continue, dear Reader!
I live in Silicon Valley, but I am not tech savvy. I am also several years out of school and realize that I my not have the vocabulary to give a precise recall of the methods and analysis described. Having said that, I feel I did learn about a (relatively) low cost technique that would be helpful in characterizing pigments on textiles. Essentially, the technique required several images to be taken at various bandwidths along the visible to near infra-red spectrum. Knowing the reflectance spectra for a given pigment allows the researcher to target the images for analysis. The targeted images are overlayed to get the difference which results in areas that appear to fluoresce for a positive identification.
It was found that indigo was readily identified, whether it was used alone or as a component of other colors. Reds and browns proved a bit more problematic. The success of this technique seems to have been that there was a small color palette, as well as the textiles in question were of known provenance, so they already had an idea of the pigments to look for. Also, the pigments were on one side and in good quantity. They did not achieve good results with dyes or small samples due to background noise interference. Though it was brought up in the question/answer portion that HPLC gives definitive “fingerprint” spectra for positive identification, the imaging technique presented does not require sample-taking (important to the National Museum of the American Indian) as well as allows for the entire textile to be mapped, keeping the pigment identification within context.
I could see this technique as a very useful first step in pigment identification or potentially in identifying areas of restoration and the pigments used. I look forward to reading the paper in the Postprints.