High-tech Archaeology

By Daiwei Mu, Triangle Writer

I recently sat down with Dr. Ann Blair Brownlee, senior research scientist at the University of Pennsylvania Museum of Archaeology and Anthropology to learn about the technology involved in the study of ancient ceramics. Dr. Brownlee specializes in ceramics of the Mediterranean region – the Greek, Roman, and Etruscan cultures – from the second millennium B.C.E. to the 3rd century C.E. “There are two main issues for archaeological museums,” she says, “research and display.” The research aspect uses present knowledge and techniques to learn more about an archaeological object. The display side deals with restoring a piece to a museum presentation level without altering its ancient condition.

The University of Pennsylvania Museum of Archaeology focuses on the display and exhibition side in its display rooms (free to Penn students), but Dr. Brownlee touched briefly on a research technique, thermoluminescent dating. Thermoluminescent dating, or TL dating, is a technique for determining the authenticity and approximate age of ceramic artifacts based on the principle of thermoluminescence. All buried objects are exposed to radiation from the environment, which causes a shift in electrical charge. While the charge shift is mostly temporary, the radiation can sometimes be stored for long periods of time. When the object of interest is heated, this stored energy is released. This is known as thermoluminescence.

When an object is kiln-fired, the radiation stored since the “creation” of its components is released. If the object were to be heated again, the energy released would be associated with the radiation accumulated since it was kiln-fired. By measuring the amount of TL intensity through a range of temperatures and by measuring the ambient radiation of the environment where the object was found, one can then approximate the age of the artifact being studied. .

Dr. Brownlee then took me to see some of the artifacts she studies. Two doors and several locks later, we came to a stash of ancient pottery. An incomplete Athenian vase depicts Heracles carrying a boar perched menacingly over King Eurytheus, who had sent him to kill the boar. I wasn’t able to make out much from the figures due to a missing piece of the pot, but Dr. Brownlee pointed the famous hero out to me easily.

Many ceramic artifacts are recovered from underground chambers and tombs. If a chamber collapsed, then the pottery inside would probably break. If a chamber stays intact, chances are the pottery will as well. By virtue of their size, smaller objects tend to survive fully-intact more than larger objects. The Athenian piece is fairly large, so it is not particularly surprising that many pieces are missing.

Ceramics also vary by texture and color, both of which are related to the clays used and the temperature at which they were fired. The Athenian piece is bright – almost orange – and extremely hard. The color indicates that the jug was fired at a high temperature, which brought out the bright color of the iron. Some of the darker pieces are softer and more brittle, almost crumbly.

She went on to tell me about the glue used to hold the pieces together. It used to be that a crude, standard glue was used for every kind of ceramic. Nowadays, there are many different grades of glue strength. “You don’t want the glue to be stronger than the fabric,” intoned Dr. Brownlee. If the glue were weaker than the fabric, then stress on the object would only break along where the object is glued. As any mechanical engineer reading this would know, if the glue were stronger than the ceramic itself, any stress on the object could cause a new crack. This would alter the original condition of the artifact, which is to be avoided at all costs.

Modern ceramic glues are also soluble in water. One need only to place an object in water and watch, over the course of a week or so, as the glue dissolved. Of course, this process requires careful supervision and the occasional change of water. Older glues have to be dissolved using special solvents. This also requires that the solvents be applied directly into the cracks – a much longer and more painstaking process to preserve the artifact.

But what happens if there are pieces missing? All the glue in the world won’t hold two pieces of pottery together if there’s nothing connecting them. If a piece is incomplete, plaster is usually used to fill in the blanks. A broken artifact is usually assembled from the bottom up in a box of sand like a jigsaw puzzle. Pieces are inserted and glued together; if a gap is completely surrounded by existing pieces, then a piece of plaster is inserted into the hole. If a large gap exists such that the object cannot support its own weight, then plaster must be molded into the gap as the object is rebuilt. Of course, ordinary plaster of Paris does not keep its shape. The plaster actually used has the consistency of putty, so it can be molded into whatever shape is necessary. It then sets into that shape permanently.

After the pottery has been set and restored, it is time to put it on display. Dr. Brownlee led me through another door and out into a current exhibit. An exhibit is a carefully coordinated effort between the exhibition curator and the project team, which includes the person creating the mounts for the items on display. The artifacts must be mounted such that they tell the story the exhibit director wants, and the story told must also weave into the stories told by the other exhibits in the museum.

There are both aesthetic and practical concerns to address in mounting artifacts. On the aesthetic side, the mount must be visually pleasing, or at least discreet. If significant pieces of the object are missing, the mount should give an idea of what the artifact originally looked like.

A display of bronze fragments along with a plastic mount outline an Etruscan footstool is a good example of display techniques. The fragments are from the bits and cheek pieces of the bridles of a pair of horses; some of the horses’ teeth are also preserved. Then there are practical considerations. A mount must, at the minimum, offer support. The less conspicuous, though, the better.

All in all, I had a great day with Dr. Brownlee at the Museum. Despite the ongoing renovations in front of the museum, Penn students should really take advantage of this world-class museum right on our campus. So the next time you’re spending a weekend afternoon with nothing to do, grab some friends to head on over to the museum!



The University of Pennsylvania Museum of Archaeology and Anthropology is open Monday through Saturday from 10 a.m. to 4:30 p.m. and on Sunday from 1 p.m. to 5 p.m. Admission is free to all PennCard holders.