LOW-OXYGEN STORAGE ENVIRONMENTS

Abstract

Several classes of materials which constitute museum specimens have been very prone to deterioration without the provision of special environmental conditions: appropriate relative humidity, temperature, and so on. Recently there has been widespread interest in the use of low-oxygen storage environments. The advantages include reduction in rate of colour fading, control of microorganisms and prevention of oxidation [1]. Many types of material can benefit from a low-oxygen environment: modern materials, archaeological materials, geological collections, and so on. In the past, objects have been treated with a variety of chemicals to stop deterioration, remove any harmful products which could cause further deterioration, and provide some form of protection albeit of short duration. This treatment, which had to be repeated continually, was the only practical solution to control ongoing deterioration processes which were obviously causing damage. One method for deactivating these harmful reactions has been the use of silica gel, since the availability of moisture is an important prerequisite for these chemical reactions. This method has been applied with some degree of success but has proved to be fairly labour-intensive, requiring considerable maintenance even if the object is kept in a wellsealed polyethene bag [2]. The new method outlined in the poster is a result of the application of the rel~tively new technology of high-barrier films and oxygen scavengers. It could be used in some cases together with silica gel. Enclosures are made using a high-barrier plastic film whose properties include low oxygen transmission and heatsealability [3]. A calculated amount of an oxygen scavenger, Ageless, is placed inside the enclosure. To produce a low-oxygen environment, the oxygen scavenger must be capable of absorbing all the oxygen present initially as well as reacting with any oxygen that leaks into the enclosure [4, 5]. In the past, due to the chemical make-up of oxygen scavengers like Ageless, their use has been restricted to environments where the relative humidity (RH) is higher than 33%. However, a new product (Ageless RP) is available which allows the effective use of oxygen scavengers at low RH. This product can absorb moisture as well [6]. Detailed studies on the use of this new product are being conducted at the Australian Museum. There are three major problem materials in the collections held at the Australian Museum where this technology can have a major impact on preservation: meteorites, iron pyrites and steel objects. The first two are from the natural science collections while the last is from the human studies collection. Meteorites (irons) from the Mineralogy Collection suffer from oxidation. This reaction is exacerbated by the presence of chlorides in the structure of the specimen [7]. A previous programme for the storage of these objects had been devised using polypropene containers to hold the specimen with some silica gel. A similar storage system was to be used for iron pyrites specimens from both the Palaeontology and the Mineralogy Collections, to slow down oxidation of the pyrites [8]. The third item is a sixteenth-century Samurai sword which had been recently restored (1978) before it was donated to the Australian Museum. A coating of Paraloid B-48N was applied to the blade to protect it while on display for six years. It was decided not to use wax on the blade because it was in excellent condition, and complete removal of the wax could be difficult, if not impossible, in the future. Once the blade came off display, a suitable storage system was required. It is now planned to put all three of the objects described above into a low-oxygen environment using the newly developed low oxygen absorber which will operate at low RH. Conventional silica gel will also be incorporated in the bag which is made from films with low permeability to oxygen and water vapour. The rate of oxidation will be monitored and compared with that of untreated samples. The Ageless RP system has some additional benefits: limited absorbency of moisture, HS, SO, HCI and NH. Vinod Daniel is Scientific Officer and David Horton James is Head of the Materials Conservation Division at the Australian Museum, 6 College Street, Sydney, NSW 2000, Australia.