Art-Test started recently working in Siena, after winning the public competition published by Sovrintendenza of Siena and Grosseto. The project includes the analyses of a selection of masterpieces, both currently exposed and in the deposits, some of which never tested before. A database of diagnostic data, Xrays, IR reflectographies, techniques and materials concerning 100 paintings from the Pinacoteca Nazionale of Siena. The outcome will provide a reliable and scientific way of comparing materials and techniques employed by the different painters, schools and periods. An indispensable tool for those studying works of art of such period and/or by the same authors. A great help for authentication and attributions purposes. It is the first time that such an ambitious project in this field sees the collaboration of public and private institutions.