Outdoor bronzes present special alteration dynamics leading to stratification of the degraded surface; the more the surface interacts with the environment, the more the stratification develops. So, alterations diversify according to longer or shorter exposure to weather agents in highly polluted urban areas. "L’incredulita di S. Tommaso" (the doubt of St. Thomas) by Verrocchio is, from all aspects, a truly interesting case. Over the centuries, it was jutting out of a niche in the wall of Orsammichele Church in Florence and just this partially sheltered position led to such diverse alterations that multidisciplinary diagnosis and analysis proved to be necessary. Thus, different scientists and institutes with different scientific instruments worked together to resolve many analytical problems and questions. The alloy and the presence of different metal phases were the first object of metallurgical tests, followed by the elemental, structural and crystallographic characterisation of both soluble and insoluble patinas. Correlation hypotheses relevant to patinas and to alteration processes producing them were then formulated. Only the meeting of such different sectors and experience, aiming at strict result correlation, enabled the successful restoration of such a famous renaissance bronze masterpiece.