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.

 

 

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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.

 

Pigment and power dressing in Roman Egypt

This is my favourite post on the British Museum blog (it appeared a couple of years ago). Now that you know about ancient polychromy research and Egyptian blue I can share it with you and it should make sense. (Or you might just think archaeologists and conservation scientists are crazy and this Egypto-Roman sculpture of Horus was actually created by Jim Henson.) Enjoy!

British Museum blog

Limestone sculpture of Horus from Roman EgyptElisabeth R. O’Connell, curator, British Museum

‘That’s one weird looking bird,’ grinned an American student on one of my tours of the Ancient Egypt and Sudan Department study collection for university students last year.

And to Egyptology students he is. And to students of Classical Archaeology too. But that’s rather the point. Roman Egypt (30 BC-AD 642) witnessed some of the most interesting, innovative and transformative combinations of traditions in the ancient world.

The god sits casually on his throne, one sandal-clad foot forward, his knees apart and draped in a garment. From the waist down, he could be any of a number of senior Olympian deities, or Roman emperors masquerading as such. He wears a feathered mail armour shirt that ends just above his elbows. His arms, now broken off, would have held symbols of power, perhaps an orb and sceptre. His cloak, pushed back over his shoulders…

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Seeing Red: VIL and IRR

In addition to UVF, we did Visible-Induced Luminescence (VIL) imaging on all the sculptures and, a couple of times, we did Infrared Reflectography (IRR) as well. In both cases, imaging is done in the near infrared range of the light spectrum. I will focus on VIL, but IRR is essentially the same (or so Mark tells me), but we used a red LED spotlight to illuminate the objects rather than the flashes. This makes for much more interesting photos and that’s why I’m briefly mentioning it here. (IRR is also regularly used in the study of paintings because it allows you to see preliminary sketches (underdrawings) underneath the layers of paint—that’s actually pretty cool.)

The setup for VIL is the same as UVF, but you mustn’t forget to change the camera and the filters on the flashes! Basically, we’d do UVF and VIL one after the other so the camera angles and distances remained the same for both series of photographs. Of course, before you do all that, you also have to take ambient light photographs of the sculpture. And to each series, you take one photo with the grey card… and another with the colour card, if it’s not already in the shot. It was a lot to think about, but we came up with a routine and all went smoothly. Although there were a couple of times when we forgot to change the camera… (Ah, hum, well, you know, we were working late in the dark galleries of the museum.)

VIL is used to detect traces of Egyptian blue—the first synthetic pigment ever made, used for thousands of years in ancient Egypt and known throughout the ancient Mediterranean. Naturally occurring blue minerals were either too precious or difficult to transform into large quantities of blue powder to create blue paint, so the Egyptians invented an artificial pigment.

Egyptian blue has the peculiar property of emitting infrared radiation when excited with a red light. Traces of Egyptian blue can easily be detected in the infrared spectrum—the pigment will glow a bright white. None of this is actually visible to the naked eye; shine as much red light as you want onto a work of art, you will not see the luminescence (bright white glow) because human vision does not extend to that part of the light spectrum. However, if you have an infrared (night vision) camera (usually a modified digital SLR camera with infrared filters), you can take an image of that luminescence. That’s what we did. We took photographs of all ancient marbles with the infrared camera when we used the flashes to excite the pigments. We found traces of Egyptian blue pigment on a few objects—some deliberately painted (like the sarcophagus fragment), others having been in contact with particles of the pigment but not actually decorated with it. (You can figure this out normally by the pattern or distribution of the luminescence.) The luminescence is so strong you can actually see single grains of Egyptian blue!

There is a great video about Egyptian blue on the British Museum website, click here to view it.  One of the photos below features Jimmy in the process of posting an image to Instagram.  To see what he posted, click here!

 

How to Observe in Archaeology

I greatly enjoyed this post and thought I would share. I love the advice to amateur archaeologists… back in 1920! (Keep up the good work, Anna!)

Ancient Cypriot art in Leeds

Recently I came across this intriguing slim volume, a guide to amateur archaeology in the Near and Middle East, produced at the recommendation of the British Museum’s Archaeological Joint Committee and published by the Museum in 1920. It was edited by G.F. Hill, Keeper of the Department of Coins and Medals at the British Museum, with individual chapters by experienced scholars.

Title page of How to Observe in Archaeology Title page of How to Observe in Archaeology

It’s essentially a ‘how-to’ guide for travellers who fancied having a go at archaeology on their way through the Near and Middle East, or in the intervals of their duties in these regions (while it is not explicitly stated, a male traveller is clearly assumed, and indeed the joint authors are all men). The Committee appear to have taken the view that the energies of amateur excavators and collectors should be directed in order to minimise damage to archaeological sites, as well as adding to scientific knowledge…

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UVF: Night at the Museum

I thought I would start my series of posts about the scientific methods we used for the study of the marbles with Ultraviolet Fluorescence Imaging (UVF imaging). Works of art are regularly examined under ultraviolet light because it reveals restorations, retouches, varnishes as well as some colour pigments, which have characteristic fluorescence under UV. (Ultraviolet light is often called ‘black light,’ something you’ll be familiar with if you’ve ever set foot in a night club.)

UVF examination and imaging needs to be done in the dark, so we worked in the small x-ray suite in the conservation lab. There are no windows there, and by closing the door, we had all the darkness we needed to look at the small marble objects (they were taken out of the galleries for the study). However, for the large sculptures (which could not be moved), we had to be in the museum galleries at night! That was a little strange…

Simple UV examination can be done with a hand-held UV lamp, which you shine on the work of art as you look at it closely (wearing protective goggles). UVF imaging necessitates a digital SLR camera equipped with UV filters set up on a tripod. The camera is controlled by a computer and photos are taken when UV light is shone on it (either with large lamps, as in the case of Hercules, or hand-held flash with a UV filter). With the photographs, you then have a record of the fluorescence of the pigments and other surface treatments and their location.

Doing UVF was like travelling back to the 80s: the ultraviolet lights, the neon colours, the bright white, and the music playing from my iPod. We had a blast! As I have had this incredible urge to watch Blade Runner since we looked at Hercules under UV on June 22, I put it on my Netflix list… and the DVD arrived today. Enjoy the post and pictures while I watch Harrison Ford and Sean Young in this 1982 sci-fi movie.