In a former post we saw that a conservator has to gather clues about an object’s past and do a lot of bibliographical research. Now let’s talk about the materials themselves and the amazing eyes of these two wooden heads.
During these last few weeks we have been busy trying to identify the materials used to make the eyes; we knew that there were three of them, one for the outer line (or eyelid), a second for the white part, and the third one for the black pupil. We first observed the eyes under a binocular microscope, which is the easiest way for a conservator to have a close look at an object.
The material used for the eyelids was immediately identified as a copper alloy because of the green corrosion products observed on the surface. Moreover we can see the metallic pink-golden surface of the copper here and there. However, the metal could have also been silver with some copper impurities; indeed when two metals are combined or in contact with each other in a burial environment, the less precious metal preferentially corrodes (also called galvanic corrosion).
To know more about the chemical composition of this alloy, we carried out X-ray fluorescence analysis (XRF), with the portable XRF device of the Lab.
Here are what the results look like:
Those peaks indicate what kind of elements we have in the metal. We learned that this is an arsenic-copper alloy, which is well-known for Egyptian artifacts. The other elements can be impurities in the metal or due to the burial environment of the objects.
Concerning the white material, the first thing we observed under the microscope was the lines in the material.
We first wondered if these lines indicated elephant ivory, since elephant ivory has unique features called Schreger lines. However, the lines in the whites of the eyes do not look like Schreger lines, which look more like cross-hatching. That’s why we then thought about tool marks; indeed, the Egyptian sometimes marked the material they used to make the white of inlaid eyes, to make them look more realistic. We quickly abandoned this theory because the pattern on the eyes is too regular and not spread across the entire surface.
So we returned to the idea that the material might be ivory, but what kind of ivory? We were lucky that our department recently acquired a complete set of ivory samples, so we could compare directly. It turned out that our eyes are made of hippo ivory. XRF analysis also revealed that the white is composed of calcium, which is coherent for ivory.
Concerning the material used to make the black of the eyes, a few paths could be followed. According to the literature, Egyptians used obsidian, glass with a black substance on the back, or other black materials for the inlaid eye pupils. The microscopic observation of the wooden statue eyes revealed that the black material is translucent with tiny bubbles. This structure could indicate obsidian, which is a natural glass. Moreover, the Penn Museum has several spare eyes in storage; comparison with these known references confirmed that the pupils of the wooden heads are indeed made from obsidian.
We will know more about the structure of the eyes by next week, since this Friday the heads are going to be X-rayed and CT-scanned !