The RKD has a unique collection of index cards compiled by the art historian Cornelis Hofstede de Groot (1863-1930). It was the bequest of Hofstede de Groot’s important archive that led to the foundation of the RKD. The index cards carry descriptions of works of art that Hofstede de Groot had seen first-hand or had come across in catalogues of auctions, exhibitions or collections. After his death, RKD staff continued adding information, and the archive grew to a total of about 1,200,000 cards.

The RKD has digitized these cards because they are an important source for provenance research and the (re)construction of oeuvres. They are also important for the reconstruction of past collections, iconographic research and can provide information about the lives of artists. The digitization project has been completed. The index cards are accessible online through the database RKDexcerpts.