The painted decorations of Ostian insulae are known by all for their excellent preservation state and for the importance they represent as one of the only testimonies of Ancient wall Painting from the 2nd to the 5th c. AD. However, it is surprising to see they have never been studied through a technical point of view, using them as a medium to understand the production dynamics of the workshops. The Hadrianic complex of the Case a Giardino constitutes an excellent case of studies, where we can follow the work of a single atelier, working together with the builders of the building and replicating the same models in a very short span of time. Recent studies have shown a very different situation for previous periods, in the Republican and Alto-imperial times, where local workshops of very high level operated in various points of the city, painting decorations worthy of the richest domus in Rome. Between the 1st and the 2nd c. AD, the status itself of wall painting changes, and it is well reflected in Ostia, where we see a radical change in the technique and the quality of the decorations. This paper will try to understand the reasons of that changing and to propose a first synthesis of the work laid by the Centro Studi Pittura Ostiense in the last years, trying to reconstruct the working of Ostian painters through time.