Silver News

Silver Ions Preserves World's Oldest Mint - Mist Keeps Building Damp but Prevents Bacteria and Fungi From Growing

During 1991 and 1992, archeologists excavating the Archbishop's Palace in Trondheim, Norway discovered several workshops dating to the late 15th and early 16th centuries. One of these workshops was a mint and may be the world's oldest such structure found.

Close examination of the single-story, timber building, parts of which had plank flooring and ceramic tiles, showed that allowing the structure to dry out would result in catastrophic shrinkage of the surviving wood and clay and further deterioration of the ceramic tiles. A decision was made to preserve the site in its damp condition and maintain its 'just excavated' look and feel for visitors and staff.

According to Professor Elizabeth Peacock Institute of Archaeology and Cultural History, Vitenskapsmuseum, (The Norwegian University of Science and Technology in Trondheim), the question of how to keep the area moist, while discouraging mold and other microorganisms that thrive in damp conditions, led to the installation of fine misting apparatus throughout the structure that emit water laden with copper and silver ions. Although both copper and silver are toxic to microorganisms, they appear to work in slightly different ways. Each is more effective against some organisms compared with others, which is why they are frequently used in tandem, says Peacock.

"The medieval mint workshop, located at the Archbishop's Palace at Nidaros Cathedral in central Trondheim and now incorporated into the new museum constructed around it, is misted four times a day for 100 seconds with water to which copper and silver ions are added. The system has been in operation for three years now," says Peacock.

So far, there is no visual evidence of fungi, algae or other plants and the museum has recently begun a program to monitor microbiological activity.

Aside from preserving the mint, the misting system has other advantages. The damp surfaces increase color saturation between the wood, clay and tiled surfaces and prevent dust from accumulating and obscuring details.

Silver News - October / November 2000