Bronze rot in a Carolingian disk fibula (800 AC) found near Maastricht

This disc fibula with animal motif is made of copper alloy and is inlaid with glass paste. The metal exhibits severe corrosion and is brittle. Saccharification has occurred in the glass paste and bronze rot is present. Bronze rot usually is
already well present before it reveals itself to the surface. Bronze rot or bronze disease is recognizable by the appearance of bright green dots and bumps that come out to the surface. Because of bronze rot, the material pulverizes, distortions, bumps and pits occur on the surface. To stabilize bronze rot, the object is immersed in benzotriazole. This should be done under vacuum. Given the relatively high cost of restoration, this disc fibula is only treated with an acid-free Vaseline, which is a cheap, but a much less effective treatment.

Source: Jean-Paul Geusen, Thorn, The Netherlands