Historical lead seals and the influence of disinfectants on the lead corrosion rate

Abstract Lead used to be a common material for setting seal to historical documents. Lead seals formed parts of historical documents as a guarantee of their legal validity. Disinfectants are commonly used during the restoration of historical documents. They successfully remove mould, bacteria and microscopic fungi from the surface of parchment documents. However, some disinfectants could also be a source of corrosion damage to lead seals. This work was carried out to examine possible corrosion damage to lead seals caused by disinfectants [a solution of carbethopendecinium bromide, a solution of glutaraldehyde, butanol (vapours), a solution of 1-propanol, 2-propanol + ethanol called Bacillol AF], which are commonly used during restoration of historical documents. The lead corrosion rates were determined by using lead resistometric probes. The solutions of carbethopendecinium bromide and glutaraldehyde increase the lead corrosion rate and corrosion products based on carbonates, nitrates and organic lead salts are formed on the lead surface. The most appropriate disinfectants for the restoration of historical documents with lead seals are alcohol-based solutions, such as butanol (vapours) and a solution of 1-propanol, 2-propanol and ethanol called Bacillol AF