Evidence of provenance

Primary sources are the most reliable: deeds of sale, invoices, receipts, probate inventories, wills, insurance policies, gallery ledgers, correspondence, shipping labels, customs reports. They are put in the file as originals or certified copies.

Their authenticity may be challenged: the tribunal may ask for the original, have the paper or ink examined, or hear the curator of the collection. Digital copies are accepted if their source is identified.

Exhibition and sale catalogues, catalogues raisonnés, press articles, photographs of rooms or studios help to place the work at a specific moment. A photograph from 1932 showing the work on a drawing-room wall is a solid indication, subject to authentication.

Written or oral testimony from people who know the history of the work is taken into account, but with caution. It must be precise, dated and corroborated.

An effective file takes the form of a chronology: date, event, owner, source. Each line refers to a numbered document. Gaps are flagged and explained rather than passed over in silence.

A five-page summary note, written by a historian, makes reading easier. Documents in a foreign language come with a translation. The tribunal may set a case-management meeting to organise production.

National archives, the holdings of auction houses and galleries, art libraries, insurers' archives, databases of spoliated property and the OIMAP Registry are the main sources. Several are digitised and accessible remotely.

The Registry keeps up to date a guide to the most useful sources, by country and period, and can direct the parties to independent historians.