The diagnostic research, realized by taking small samples and their chemical-physical laboratory study, is important to complete the information gathered by historical research and the on sigh investigation and resolve problems of interpretation on the state of materials and forms of alteration present . Thus it is defined as an initial diagnostic project with an indication of the problems, the types of analyses to be made and the quantity and the location of samples to collect.

The tests can be performed on-site or in the laboratory. The ones on-site may include the structural characterization and the identification of instabilities in place (through surveys, core sampling, endoscopies, flat jacks, monitoring of lesions), or the characterization of the surfaces (evidence of restoration, testing the efficacy of products used on site such as colorimetry or capillary absorption). Instead, the laboratory analyses are designed to investigate the state of conservation at microscopic level: optical and electronic microscopes are used for the compositional and conservative characterization, other instruments for the resolution of specific questions (presence of salts, organic substances resulting from previous treatments, natural or induced alterations, biodeteriogens organisms attacks, recognition of executive techniques

The results of the diagnostics allows a sufficiently clear definition of the problems founded and then the actions to perform on the manufacture; so, under construction the operators will have a wide-ranging draft, accurate, easily accessible and solving specific issues, in short "variables proof”.