The basic function of a museum control system is the introduction of moist air into the environment during dry periods and the removal of moisture during humid periods. The chemical treatment of the water used in the humidification system (to prevent pipe corrosion) is common. Additives include hydrazine and volatile amines like diethylaminoethanol (DEAE). Residues of these additives settle on works of art. While the toxicity of DEAE is known, the effects of DEAE residues on objects have not been well investigated. However, alkaline pollutants darken oil-paint films and discolor dyes and may react with acidic pollutants to form hydroscopic salts which may corrode metals. Replacement of open humidification systems with closed systems or regular maintenance and cleaning of condensed films from exposed surfaces will reduce the risks.