Pursuant to article 6 of the State-Owned Museum and Spanish Museum System Regulations (Royal Decree 620/87, of 10 April), the departure of cultural assets assigned to State-Owned museums for participation in temporary exhibits must be pre-authorised by means of a Ministerial Order. Moreover, the loan of any works from the Cerralbo Museum collection must be pre-authorised by the Foundation Board of Trustees.
If you would like to request a loan of national collections that are part of the Cerralbo Museum, the petition for the piece or pieces must be made in writing (See request form) and sent to the Museum Director indicating the title of the exhibit, the dates, organizer, pieces requested and future locations with the Facility Report or a report on the technical conditions of the future exhibition rooms. After approval by the specialists, who will assess the state of conservation of the pieces requested, among other things; and approval from the Cerralbo Museum Board of Trustees, the administrative procedures will be initiated with the Spanish Ministry of Culture which owns the collections. The process will end with the departure of the piece or pieces from the museum, their participation in the requesting temporary exhibit and their return after completion of said exhibit.
You may find more information at the Spanish Ministry of Culture website.