A Note on the Evaluation of a Solid-state Air Drier

Abstract

Ancient bronzes in the collection of the J. Paul Getty Museum are maintained in low-humidity environments to eliminate the possibility of recurring chloride corrosion. A small, low-power, solid-state air drier was considered as an option to silica gel. This relatively new technology combines electrolytic dissociation of water molecules to hydrogen and oxygen with membrane separation. Hydrogen atoms formed on the anodic side penetrate the membrane and combine with oxygen on the cathodic side to form water. Oxygen atoms that remain on the anodic side recombine to form oxygen molecules. The process of water removal was found to be very efficient, but it is suggested that a portion of the oxygen atoms might react further to form ozone, a reactive molecule generally regarded as a deleterious pollutant in museum atmospheres. This was confirmed by passive sampling for ozone using diffusion tubes. While control levels after 60 days ranged from 0.43 to 1.25 parts per billion (ppb), samplers in the test environment recorded a level of 10.5 ppb, an increase of approximately 10 to 25 times. Developments in solid-state driers may overcome this problem in the future.