The blue background of this cartonnage fragment appears very dark when viewed under normal conditions, but under the microscope, a brighter blue color can be seen underneath. This blue resembles Egyptian blue, a synthetic pigment made by heating a combination of copper, white sand, chalk and a sodium salt such as natron. The result is a solid, glassy material that can be used to make whole objects, such as this small covered jar in the Walters Art Museum.
Egyptian blue can also be ground up as a pigment and used to paint. When it is first applied, it appears brilliant blue, but over time the pigment oxidizes as it is exposed to air, and becomes darker.
To confirm that the blue pigment on this cartonnage fragment is Egyptian Blue, a special digital photographic technique called visible-induced infrared fluorescence (also known as ‘luminescence’) was performed. Egyptian blue is a material that absorbs some visible light and emits lower energy, longer wavelength radiation in the infrared portion of the spectrum. This fluorescence is not normally visible, because the human eye cannot perceive the infrared, but with specially modified camera equipment, it can be recorded.
The very bright infrared fluorescence of the blue background confirms that it is indeed Egyptian blue. Because this pigment is known to darken when exposed to air, it will be stored in a closed container to limit air flow in order to preserve it for future study and exhibition.
By using examination techniques that do not damage the object, it is possible to characterize many of the materials that were used to create this cartonnage. Now that conservators know more about these materials, it is possible to make recommendations about how best to store this object so that it will not continue to deteriorate. The fragment will be placed in a closed container to protect the fragile surface from accidental damage and the Egyptian blue from exposure to the air. It will be kept in the dark or in low light to protect the orpiment.
Understanding how the materials on this fragment may have changed over time also allows conservators to make a guess at how it may have originally appeared when it was first made. The reconstruction below is speculative, but it gives some impression of the bright, contrasting colors that may have originally decorated the larger mummy bundle from which this fragment was removed.