Reading the past in crystals

We meet at Geoscience in Aarhus and stop by the kitchen to grab a coffee before Heide lets us into the lab.

“That’s where I took the photo,” Heide told me on the phone earlier in the week when we set up the meeting.

Heide tosses her bag and jacket onto a chair before sitting down in front of one of the microscopes in the long, narrow lab. She lifts the lid of a cardboard box, takes out a small epoxy block with a piece of metal embedded in it, and places it under the microscope. After adjusting the lens and pressing a few buttons, an image appears on her computer screen.

“We’re looking at a tiny piece of a round belt plate from the Bronze Age. It was found in a woman’s grave, and we know from multiple other digs that it’s part of a woman’s outfit.”

The screen displays multi-colored images. It takes an expert to see the resemblance between them and a beautifully crafted bronze plate. Heide explains how the small piece of metal has been ground, polished, and then etched to reveal the different layers of crystals.

“These crystals show that the bronze has been melted in a pot, cast and heated several times, but that the blacksmith didn’t do much work on the design and decoration,” Heide explains and points out that this settles a feud over whether the tools used to work on bronze during the Bronze Age, 12–1300 BCE, were also made of the same metal.

“Back then, bronze, bone and stone tools were the only kinds available, but this metallographic analysis method, introduced to Danish archaeology by the metallurgist Vagn Fabritius Buchwald, allows me to show that the blacksmith who made this belt plate used bronze tools. And that’s what I wanted to show with the photo I submitted for the competition.”

Microscopic game changer

Heide leans back in her chair and turns away from the microscope before she continues.

“This method has totally transformed our field. For example, I can tell what metal an object is made of, which isn’t always possible during a dig. I can tell what kind of object it is. Under the microscope, I can see whether a small piece of iron is from a dagger or a knife, for example, and calculate its age. From the craftsmanship, I can tell how far advanced the blacksmith’s knowledge of metallurgy was at the time the object was made.”

Heide argues that this knowledge is valuable because it provides insights into the blacksmiths’ expertise, skills, and how often they made bronze pieces.

“We’ve also learned more about how knowledge was passed on in Europe: In Denmark, we specialized in casting; elsewhere in Europe, they focused far more on forging. But objects from back then also show clearly that knowledge was shared across borders.”

Heide is also passionate about interdisciplinary work and believes that science can provide valuable insights into our ancestors.

“We can see how our knowledge of technology has changed, and that it has done so many times. We can also see which social changes have spawned new technology, and there is a chance that we will be able to use that knowledge of the past to change the way we behave in the future.”

See interview with Heide Wrobel: