Pigment sampling

Now that we know there are traces of pigments on some of the Classical sculptures, it is time to take samples of all colours found on these objects. This task falls to Mark, who has to take minuscule samples of the pigments using the microscope or a head loupe to see them. Sampling will enable us to conduct further experiments (or have them conducted by a lab) to confirm the nature of the pigments with other scientific methods.

 

 

XRF: X-Ray Fluorescence

After having identified the sculptures that still bore traces of pigments, the next step was to do x-ray fluorescence. This is a non-invasive technique used for the identification of non-organic pigments. It is not enough to note the presence of pigments on sculpture and take photographs of their location; we need to know of what these mineral pigments are made. This helps with the dating and authentication of the work of art because certain pigments are used in specific countries (or cultures) or during specific historical periods.

The analysis was conducted by Scott Pike, associate professor of geology and earth sciences at Willamette University, who had in his luggage his very handy x-ray gun. While we worked together, Scott explained how this Star Trek phaser looking thing works. This instrument send x-rays on the non-organic matter we wish to analyze. This results in electrons being bumped from their atomic orbital positions, releasing a burst of energy (fluorescence) that is characteristic of specific elements (elements of the periodic table, that is). The fluorescence is identified and recorded by the device. Each pigment will have its own combination of elements. Thanks to this technique, we can tell if the red pigment is actually red ochre (an iron oxide used in ancient Egypt) or cinnabar (mercury sulphide used by the Romans).

The x-ray gun is controlled with a computer. Although I did have my photo taken with very cool looking instrument (I just had to!), I assisted Scott by manning the computer while he held the portable XRF device to do the analysis. Elizabeth joined us in the galleries for a while and that allowed me to take a few pictures. Luckily, x-ray fluorescence does not require to be done in the dark. So we didn’t have to work late nights at the museum. All we had to do was stanchion off a work area around the sculpture under examination so that people did not disturb us… but we did have some people intrigued enough to stop by and observe what we were doing.