This British patent specification number 396,439 describes methods for controlling optimum humidity (Rh) levels in enclosed spaces by means of solid chemical mixtures (of hydrated salts) capable of absorbing and releasing moisture at prescribed levels to protect objects from mold, fungi, condensation, etc. Avoid substances capable of supporting bacterial growth or producing volatile decomposition products other than water vapour. Applications include the preservation of works of art (wooden panel paintings, drawings, prints, etchings, etc), frames, books, documents, and other moisture sensitive (hygroscopic) items (artifacts) exhibited in cases or hermetically sealed storage chambers. Improper environment may cause embrittlement, efflorescence (bloom), warping, etc. This patent is a reference for museum environment and conservation.