Correlation between two units consists in considering one deposit to be the same as another. In identifying non-original layers and their relationships can we obtain data with which to work. In this way, assigning functions and correlating or phasing the units or, in general, grouping them, we can interpret and give meaning to the stratification studied. The final aim is to be able to go from pure, isolate material data to more far-reaching information related to the contexts which have exerted an influence on a work and thus conditioned its evolution. One of the most important consequences of this focus is that cleaning is defined as a way of recovering and preserving information and not just as a merely aesthetic process.