The historical archives of the Italian astronomical Observatories are a source of incredible treasures. They contain records of observations, sketches of astronomical objects (nebulae, comets, planets), letters, diaries, journey logbooks, meteorological data, maps, astronomical calculations, etc. Over 3 million documents, 122 series containing the funds of various astronomers are preserved in 12 historical archives. Rearranging these records is a long and hard task comparable to solving a puzzle not knowing how the finished picture will turn out, but we certainly know that the reorganization will constitute a fundamental resource for the study of the history of astronomy. The web portal “Polvere di stelle [Stardust] : the cultural heritage of Italian astronomy” (http://www.beniculturali.inaf.it/eng/) contains a specific section dedicated to the historical archives. It provides a brief descriptions of each archive and the possibility to consult the tree structure of the inventories and to make a search in all database fields. In 2018 a digitazion project of selected archival documents began and the 18th century meteorological registers from Padua and the solar observations made by Pietro Tacchini and Angelo Secchi in 19th century are now available on “Polvere di stelle”. This contribution will show benefits and problems encountered in dealing this particular aspect of preservation and valorization of the astronomical heritage.