A scientist, a curator, and an archaeologist discuss the exciting discoveries revealed by the scientific analyses of an ancient Greek funerary stele.
Marco Leona: I'm Marco Leona, the head of the Scientific Research Department at The Metropolitan Museum of Art in New York City. I'm here in the New Greek and Roman Galleries, looking at an ancient Greek funerary stele from the late fourth to early third century B.C. I'm with two colleagues who have been studying this object with me from two perspectives that are very different than mine: Joan Mertens, curator in the Greek and Roman Art Department; and Mark Abbe, doctoral candidate in archaeology at New York University.
Joan Mertens: The object that we're looking at is a tombstone and it was made and it was found in northern Egypt in the area around Alexandria. And during this time, which we call the Hellenistic period, Alexandria was an extremely important center with a very cosmopolitan and international population. And in the cemeteries there, we have evidence, especially from inscriptions, of the many foreigners who were buried there, and we know that quite a few of them were mercenaries. The object that we are looking at is very traditional in many respects, and this is why the opportunity of working with two scientific colleagues is so exciting, because it opens up entirely new perspectives that curatorial people like us would not otherwise be aware of.
The form of the tombstone, with a pediment on the top and this architectural aspect, was really established at the end of the fifth, the early fourth century B.C. on the Greek mainland and particularly in Athens. And the subject that we have here of someone who has died, who was taking leave of his family—this also has been known on the Greek mainland since the end of the fifth century B.C. And even the fact that there is painted decoration is also, at this time, nothing new. What is very new and very exciting is what our scientific colleagues have been able to discover.
Mark Abbe: We first examined this stele under a microscope, and then you'll notice all of the different colors that you see. And we did a series of material analyses using X-ray fluorescence spectroscopy, X-ray diffraction, and other techniques that allow us to identify the pigments that you see. One of the fascinating things in our study of this piece is that the yellow pigment that you see on the garment of the central figure is, in fact, a new pigment, unidentified to date. It is a lead-arsenate mineral known as mimetite, and if you scan the Mediterranean basin and look for where this specific mineral may have been found, we find it really in only one place in any degree of significant concentration: the silver mines of Athens at Lavrion, which we know were in their peak of production in the fourth century. It was the silver from these mines that really funded the Athenian empire, in a way. And the discovery of mimetite at these mines really has, to date, not been properly recognized.
Mimetite appears naturally as a yellow particle on the exterior, forming almost like a crust, on the dark, black, galena silver ore. And so, what appears to be the case here is that an artisan or someone working in the mines scraped this yellow crust off and began to use it as a pigment in the Greek palette. This mineral was presumably imported into Alexandria where it was used on the stele.
Marco Leona: Mimetite was not the only yellow pigment available in the ancient classical world. An artist would have had a choice of pigments such as ochre—so, iron oxides that are extremely abundant and widely found—or the more rare and costly orpiment, which is a very warm, rich yellow-in fact, it means "the color of gold". What is significant here with the discovery and use of mimetite is really the connection to an Athenian formation for these artists. The fact that the pigment would have been immediately available and noticeable by artists in Athens. It probably, when originally painted, was a very bright, highly reflective yellow, because that's one of the characteristics of lead pigments—they have high refractive indexes, which, in turn, give a very strong color contrast.
The artists in the classical world had access to a variety of pigments of all colors, and that's also significant for us—if you want, from a different perspective than the art historian or the conservator, that of a scientist—because it opens a window into the chemical and scientific knowledges of our ancestors. They would have used a variety of minerals, finely crushed, such as mimetite, such as the ochres ranging from yellow to brown to orange to red. They would have access to natural and semi-synthetic pigments, such as the various lead pigments—lead-white, red-lead. They had discovered—a discovery inherited from the Egyptian tradition—synthetic mineral pigments, such as Egyptian blue. And they had even mastered the art of turning vegetal or insect extract into color, and those would be bright shades of pink that were obtained by fixing the juices of some roots on clays or on alumina—a technique that we find, up to this day, in the use of natural dyes for textiles.
Mark Abbe: One of the great things about understanding the materials that an artist used is it really allows us insight into the working practices of ancient artists. If you look at this stele, at the center, you'll see the central figure—his hair appears to be blue. It did not appear this way in antiquity. Rather, this is actually the Egyptian blue that Marco mentioned, and it was used as an under-paint to obtain a very rich, complex, black tone. The whole reverse of the painted scene that you see at the center of this stele was prepared with a lead-white ground. This was a new innovation during the Greek classical period and it allowed the painter to really maximize the color effect and color values obtained through the different pigments that Marco has been mentioning.
Marco Leona: Now, one question that any visitor would have is how is this scientific work done, and what it requires, both of the scientists at the Museum and of the piece that's being examined. What we have here is an object that has survived for 2,300 years. It looks as—most of the color is gone, the image is somewhat fragmentary, but we should regard the fact that there's an image at all as exceptional. Very few works survive from classical antiquity with their entire polychromy extant. So for us, in a museum, it's extremely important to respect the integrity of the piece. Now, analytical chemistry requires, very often, a pretty invasive approach. Something has to be removed and then processed in our instrument.
Here at the Museum, we specialize in obtaining analytical information without this type of invasive approach. So some of the techniques that have been used, such as X-ray fluorescence spectroscopy, can be applied in a completely noninvasive way. It's a small instrument that approaches the surface of the piece, shoots X-rays at the pigments, and captures the scattering of these X-rays and the interaction of the primary X-rays with the substrate, deriving a fingerprint for each type of pigment. Other approaches include Raman spectroscopy, where a laser beam is used to excite a response in the minerals present in the pigment layer. That, in turn, gives rise to a fingerprint spectrum of the material used.
Finally—and that's actually how we analyzed mimetite, identified mimetite—something that's required for the most complex and difficult cases, we may have to remove a microscopic fragment, in this case something in the order of twenty, thirty, fifty microns, which is, commonly, the diameter of a human hair. That small fragment was then analyzed in an instrument called an X-ray diffractometer, which gave the crystallographic fingerprint of the mineral mimetite. All this work, of course, is done in collaboration with the curatorial and conservation department. You can imagine that the importance of the piece, the correct identification of the painting layers, the remains of polychromy, and the scope of the analysis—the sampling required—require a constant consultation between the professionals involved in the study.
Joan Mertens: This is, really, the most exciting part of such a collaboration, and this is the very exciting aspect of what can be done here in the Museum, that a variety of disciplines—some which are relatively traditional, such as the curatorial disciplines, with a long tradition of scholarship and of visual analysis—that we're able to come together with pros in the contemporary disciplines of science and open up entirely new aspects and horizons about, in most cases, relatively well-known classes of material. But through these new processes, they gain entirely unexpected and extraordinarily exciting new dimensions.
Marco Leona: If you would like to learn more about how collaborative work in art, conservation, and science can lead to new discoveries about works of art, we invite you to come to The Metropolitan Museum of Art to hear a new Audio Guide program: "Investigations: Art, Conservation, and Science." Information about the Metropolitan Museum and its programs is available at metmuseum.org.
The Audio Guide program at the Metropolitan Museum is sponsored by Bloomberg.
This has been an Antenna Audio production.