Museum paintings conservation includes restoration and conservation of exhibited works, loans of works for special exhibition or for temporary deposit outside the museum, and preventive conservation of works in storage, which are no longer exhibited except on rare occasions. A museum collection is usually formed from varying provenances: the collection at the Museo San Pio V includes objects belonging to the museum, to the Real Academia de San Carlos (Royal Academy of San Carlos), and from donations and proceeds from the 19th-century public auctions of church or aristocratic property. The most frequent deterioration cause is natural ageing, but deterioration can also be caused by external causes such as improper treatment, often by those not trained in proper criteria for paintings restoration, physical-chemical deterioration due to aggressive environmental fluctuations, accidents, lack of housing during storage, etc. The article provides practical examples for observing the criteria observed in different types of restoration: the criteria include paying particular attention to re-lining practices with different adhesives, cleaning and reintegration. Accurate preliminary study is crucial so as to prevent damage to the object due to inappropriate conservation decisions.[Abstractor’s note: author cites 11 illustrative figures, which however are not provided in the article.]