Ur Digitization Project: March 2013

March 28, 2013

This month we had a week-long visit from archaeo-metallurgists from the Deutches Bergbau-Museum, the University of Franfurt am Main, and the University of Toulouse, Le Mirail. They brought with them some impressive equipment for spot analysis of many metal objects from Ur and will do more in-depth studies of the results back in their home countries.

Some of their analysis was conducted with microscopes to investigate tool marks and better understand the way in which these objects were made. Another aspect was the analysis of chemical structure. This might normally require invasive techniques, but these scientists brought with them a non-invasive portable X-Ray Florescence (XRF) machine. Looking something like a radar gun that might check your car’s speed, it fires X-rays at an object and measures the return. From this it can tell the composition of the metal at the surface.

Let’s focus on one particular object they analyzed:

Artifact of the month
Spotlight on field number U.9339 (museum number B16691)
Gold or Electrum Adze-head

Adze U9339/B16691 : Made of gold? How much gold?
Adze U9339/B16691 : Made of gold? How much gold?

This is the head of a tool known as an adze, something like a cross between an axe and a hoe. Often used in wood-working, this particular tool was found in a royal tomb, PG 580, along with many other tools and weapons. What makes this adze particularly interesting is that it appears to be made of gold. In this same tomb were also found two gold chisels, a gold javelin head, and a gold dagger. Many copper tools and arrow heads, as well as a silver belt were found here too, but no human bones — a curious result for a grave. At first the dig director, Sir Leonard Woolley, believed this to be an offering chamber rather than a burial. Later he suggested that most of the bones in the tomb had deteriorated beyond recognition. He offered this explanation on p. 48 of Ur Excavations 2:

“…occasionally a skeleton might be almost intact, in another neighbouring grave the body, though undisturbed, might be reduced to a scarcely distinguishable brown dust with perhaps a splinter or two of quite hard bone; often of a single bone, or of a skull, one half would be solid and intact and the rest would have disappeared completely.”

There are many questions related to PG 580 that have yet to be answered. Some of the problems arise from the method of excavation — it was actually cut into from the side rather than from the top down. This was the first of the ‘royal’ tombs to be encountered and the excavators hit it from the side of Trench E at the very end of the 1926-27 season. But this isn’t the place to go into all of the questions and difficulties of the evidence. The point here is to concentrate on one particular artifact in the grave, the adze U.9339.

Plan drawing of PG580. Number 16 on the plan is the adze U9339.
Plan drawing of PG580. Number 16 on the plan is the adze U9339.

The adze (no. 16  on the map) was found near the center of the large grave, the floor of which was some 14×20 feet. Evidence of its handle was clear — it had been wrapped in places with thin gold bands. The end of the haft was beveled and clad in gold with a copper nail to hold it in place. Nearby was the silver-clad belt with gold dagger (nos. 20 and 21), many beads (no. 19), and two copper adzes (no. 17). If there was a primary body here, it was surely wearing the belt and dagger and thus the adze may have been held in or near the hands of the deceased. But was it really made of gold?

Moritz Jansen operates the portable XRF machine to determine the precise content of the metal of adze U9339.
Moritz Jansen operates the portable XRF machine, analyzing metal composition.

A German doctoral student operated the XRF machine, bombarding a 6 mm portion of this very adze with X-rays. After two minutes, the computer screen displayed the results:

55% AG (silver)
40% AU (gold)
5% CU (copper)

The readings are more precise than that, with minor occurrences of other elements that may eventually help us to locate the source of the metals, but I show the major results. There is a high quantity of silver, even more than most electrum ores. Electrum can occur naturally, but the silver here was probably added as an intentional alloy. Why? The first thought might be to make it stronger, so that it might function as an actual tool. But copper would be the choice to add if that were the goal, silver doesn’t make the metal that much stronger. So the main reason must have been for the color, or aesthetic appeal, to show that this person was important or wealthy. Mesopotamians did understand alloying and their texts sometimes refer to ‘white gold’ and ‘red gold’, probably gold mixed with silver in the first case and copper in the second. Somewhat contrary to what you might expect, red gold tended to be more valuable, though admittedly we don’t have a lot of evidence of the relative values.

Analysis of this object has led to many more questions, but such is the nature of research. We learn by investigating things, often things we thought we already knew. That’s why we need all the information from Ur to be gathered together in one place, available for study — the main goal of the Ur Project.