Despite their presence in many museum collections as testimony to the great technological advances of the late 19th century, aluminium alloy objects are rarely exhibited or may even be discarded because of their unattractive surface appearance. Conservation professionals are often helpless when faced with these materials which they consider to be unalterable but whose composition, desired appearance during their manufacture, successive uses and corrosion forms developed over the long term are not well known. Any diagnosis is therefore extremely uncertain. The objective of this project was to cover this gap and provide conservation professionals with examination tools and diagnostic assistance. This approach has been applied to more than 400 objects preserved in four Swiss museum or private collections and considered sufficiently representative of the problems posed by aluminium alloys. The materials were systematically analysed, the corrosion forms developed identified, characterised and compared from one collection to another. Some alterations were examined in depth and the observed models were inserted into the MiCorr participatory database (micorr.org). The results obtained should make it possible to appreciate better the nature of the materials studied and understand their long-term performance in order to propose, if necessary, appropriate interventions