In the Middle Ages to early modern times in Northern Europe, some elite burials included a lead cross placed on the deceased’s chest to facilitate the passage to the next world. These funerary crosses typically had an inscribed prayer and sometimes the name of the deceased. Over the centuries, the lead corroded in the damp earth which continued once exposed in air despite the fact that lead is often thought of as a corrosion-resistant metal. That corrosion layer can obscure a reading of what is written on the cross.
In a collaboration between Georgia Tech, a conservation lab, and a museum in France, we used a novel imaging approach using terahertz electromagnetic waves to peer below the corrosion without removing it. Terahertz waves are similar to microwaves, but with somewhat shorter wavelength. Using a combination of clever data analysis approaches (not my idea, but those of a talented PhD student!), we were able to read the hidden inscription. There are many other types of lead artifacts in museums, including sarcophagi, cups and plates, decorative items, and sewer and water pipes where this technique might be used. This approach is of interest to art historians, conservators, and archeologists.
