Conservators in the BKM Conservation Lab have been hard at work preparing objects for a number of up

Conservators in the BKM Conservation Lab have been hard at work preparing objects for a number of upcoming exhibitions and traveling loans. One upcoming exhibition will focus on the use of blue in a variety of different cultures across time. We have therefore begun examination of several objects containing blue paints, paint mixtures and dyes to determine what colorants they contain. New imaging and analytical techniques available in the lab allow us to identify pigments without sampling.Previously, we described our use of Visible-Induced Luminescence (VIL) imaging, which can be especially helpful for identifying the use of Egyptian blue on ancient Egyptian objects. While we used this technique to identify Egyptian blue on this piece as well, we will be elaborating on that finding in a future post.We have recently begun trying to identify indigo on some pieces in our collection, beginning with this colorful Footcase of a Mummy. Indigo is a plant-derived dye that was a common blue colorant for Egyptian textiles, but is more rarely identified in paint mixtures. Specialized multiband imaging techniques, as described in previous posts, can allow us to map the presence of indigo on the surface of an object using a modified camera, filters and image processing. This technique is more thoroughly described here, in this blog describing its use at the Smithsonian’s National Museum of the American Indian to identify indigo on Andean textiles. Essentially, two different infrared images are photographed at slightly different bandwidths and the difference between these two infrared images is subtracted, rendering certain materials, such as indigo, as bright regions, as seen above.  In the painted cartonnage, the outlines of the feet and border patterns that appear white indicate that indigo is likely present. However, multiband imaging does not provide a precise identification, and we must keep in mind that other pigments, such as lapis lazuli, can respond the same way when using this type of imaging. Therefore, the presence of a specific pigment, paint or dye needs to be confirmed with other techniques as well. In this case, we have also analyzed several sites on the cartonnage with Fiber Optic Reflectance Spectroscopy (FORS) to confirm the presence of indigo. This technique is also relatively new to the lab and was used by Jessica Ford in her analysis of Stuart Davis’ paintings. As opposed to imaging which maps the entire surface of the object, FORS excites a very small area of the object and provides a reflectance spectrum that is unique to the materials in that site. Our preliminary analysis with FORS indeed seems to confirm the presence of indigo, but the data require more analysis for a definitive conclusion to be made. Stay tuned, as we will be continuing to use these techniques to corroborate the identification of blue pigments on objects in the collection.Posted by Dawn Kriss and Sara Levin -- source link

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