The Kelsey Museum’s collection of Roman construction artifacts includes a wide range of building materials, such as lead pipes, marble cladding, and volcanic opus reticulata. Among the most significant items are a group of stamped bricks, many of which were purchased by Francis Kelsey for teaching purposes. The stamps on these bricks help scholars date ancient structures and gain insights into the Roman brickmaking industry. However, when researchers open the storage drawers, they often encounter a problem: many bricks are covered with a layer of white, fuzzy crystals, making the stamps nearly impossible to read.
We knew that this mystery fuzz was likely made of salt crystals—not an uncommon problem with archaeological ceramics—but in order to treat and prevent them from regrowing, we needed to answer some questions: (1) What kinds of salts were these crystals? (2) Why did they form in the first place? (3) How can we safely remove them?
During the 2024–2025 academic year, the Kelsey Conservation Department hosted Kathryn Peneyra, a conservation graduate student from UCLA/Getty, for her final practicum year. Kathryn skillfully addressed all three of our questions about the white fuzz. With assistance from Christina Bisulca, conservation scientist at the Detroit Institute of Arts, Kathryn identified the fuzzy crystals as thecotrichite—a type of salt that forms when artifacts are exposed to acetic acid vapors released by wooden cabinets. Our stamped bricks had been stored in such cabinets before they were moved to the Upjohn Wing in 2009.
That answered questions 1 and 2. For question 3, Kathryn evaluated two different treatment approaches, including mechanical removal of the salts with a brush, and desalination using successive baths of deionized water. Salts can cause damage to artifacts when they crystallize, but because Kathryn had identified the salt and knew how it responds to humidity levels in the air, she determined that the salt poses minimal risk to the bricks in the Kelsey’s climate-controlled storage. Her recommendation is to keep the bricks where they are and to carefully brush away the white fuzz to reveal the stamps.
