By Caroline Roberts, Conservator
Suzanne and I are busy preparing for the data-gathering phase of our NEH-funded Color Research project, which is scheduled to begin next month. We’ll be investigating color on 200 ancient objects from Karanis, Egypt, including about 40 textile fragments.
Among the tools we’ll use is multiband imaging (MBI, previously referred to as multispectral imaging). MBI is a photographic technique that can be used to characterize textile dyes, and we’ve added a new method to our MBI toolbox: multiband reflectance (MBR) image subtraction for indigo—a blue, plant-based dye used in Egypt during the Ptolemaic and Roman periods.
Indigo dye molecules absorb a lot of light at 660 nanometers (the end of the visible light range) and reflect a lot of light at 735 nanometers (the start of the infrared light range). We can capture these contrasting behaviors by using lens filters that allow the camera to record these specific wavelengths. When we combine images captured at 660 and 735nm using the “difference” blend mode in Photoshop, areas that contain indigo (which absorb and reflect at those specific wavelengths) appear white. On textile KM 13821 you can see that the dark blue horizontal tapestry bands contain indigo dye. This technique will be useful for identifying indigo and for mapping where indigo is located on an object. The latter will be helpful in areas where dyes have been mixed to create a modulated color and in places where the original color has faded or discolored over time.
We look forward to sharing more colorful discoveries like these as this project unfolds. Stay tuned!
