The National Gallery is a museum that houses many great works of art, including paintings, prints and drawings, small and large sculptures, etc. The artworks differ in size and construction, as do the materials used in the construction of these artworks. The museum has undertaken the protection, safekeeping and care of artworks. The museum's art conservators care for each one of the museum's works individually. When undertaking the conservation of an artwork the basic rules that inform their profession are always taken into account. For example, they choose appropriate materials when treating a work and they try to use materials (e.g. adhesives, solvents, varnishes) that are as ""reversible"" as possible. ""Reversible materials"", in the language of conservation, means that the materials used on the artwork during restoration must be removable in the future if necessary. Conservators attempt to perform the minimum treatment necessary, working to secure the durability of the works while interfering as little as possible with their integrity. Conservators respect the work of each artist and take care not to alter the original image with their procedures. Maintenance procedures carried out vary depending on the works. Depending on the type of artwork and the materials of its construction the conservator decides which procedures (maintenance) will be done.