O Escurecimento do Altar da Sé do Porto: Um Caso de Corros？o Atmosférica

samples taken from the different zones of the silver altar of porto？s cathedral were characterized by morphological and analytical techniques. it was concluded that the material used in the altar piece was ag:cu alloys with ag ranging between 62.9 % and 97.8 %. concerning to the corrosion products it was possible to postulate the existence of silver compounds, as chlorides, and copper compounds, as oxides and sulphates. other products identified related with the environment were the sodium and potassium sulphates and aluminosilicates, apart from some cleaning residues.