Deterioration of tin-rich organ pipes

Tin-rich organ pipes are often affected by localised deterioration in the form of grey pustules, pinholes, cracks and exfoliations at the surface. Two main types of decay of tin-base materials that might have a similar appearance, i.e. the surface of the object covered with dark grey pustules, are known. The first is the allotropic transformation of white metallic tin into grey tin, the so-called “tin-pest”. The second form of decay is due to corrosion in the form of localised oxidation of tin. The identification of the causes of deterioration is of main concern because, whereas oxidised material can be treated, an object that suffers “tin pest” cannot be reconstituted. In the present paper the results of investigations on ancient tin-rich organ pipes affected by localised degradation are presented. The study of the composition and the microstructure of the pipes has been coupled with the results of analyses on the corrosion products. It was shown that oxidation clearly has a significant role in the deterioration of tin pipes, but it was not possible to establish if the allotropic transformation took place or not, because of the low probability of detecting the residual grey tin.