The National Directorate for Conservation Archives is the most extensive in the country, comprising original documentation on National Heritage Sites. The archive comprises approximately 210,000 drawings and sketches dating back to mid 19th century. The nucleus of the collection is the archive transferred from the National Heritage Association when the Directorate of Conservation took over responsibility for the accumulated heritage sites in Norway in 1988. It includes the Norwegian portrait archive of 11,000 negatives of artistic portraits of Norwegians, the photographic collection dating back to the 1870s which totals 510,000 photos from all around Norway, a slide collection, a scientific archive featuring reports, correspondence etc on construction work on national heritage buildings and various news clippings collected since the 1920s. There are also some extensions to the collections outside the building. See also National Directorate of Cultural Heritage.