The reversal of lead sulfide blackened earthenware glazes by means of outdoor exposure to sunlight

Abstract

Lead glazes on earthenware can undergo blackening in anaerobic environments as a result of the formation of black lead sulfide within the glaze due to microbiological activity by sulfate-reducing bacteria over many decades. In this article the results of a recent campaign of roof exposure in Lisbon, incorporating environmental data, give a better understanding of the factors which bring about the glaze transformation. Accordingly, the potential for optimising the efficacy of this novel, eco-friendly treatment in the future is enhanced.