The Oriental Institute contains a collection of archaeological iron objects that is maintained at 25% relative humidity. It is commonly understood that unstable archaeological iron requires a much lower relative humidity to prevent further deterioration. This problem has been the subject of much study over the years by the conservation community.
Research into this topic at the Oriental Institute began as part of a 1998-1999 Getty post-graduate intern research project. After extensive review of the literature, it was decided to focus on a new and, at the time, minimally researched storage system developed for metals by Mitsubishi Gas Chemical America, Inc. called the RP system™ A-type (formerly known as the “RPA system”). The RP system™ A-type utilizes an oxygen scavenger and a desiccant to provide an oxygen depleted and low relative humidity microenvironment. The RP system™ A-type differs from Mitsubishi's previously developed low-oxygen system (Ageless) in that it also maintains a desiccated environment.
Even at the beginning of this research it was realized that, if the RP system™ A-type is as effective and safe as advertised by the manufacturer, it could prove to be an excellent storage system for archaeological iron. The initial focus of this project involved determining whether the product could safely be recommended as an inert, non-reactive and effective storage system. In its early stages, the research was centered on brainstorming the parameters for the testing protocol and determining the equipment that would be necessary to carry it out. We felt that it was important for us to independently evaluate the claims of the manufacturer as well as the possible unintended effects of the product on metal.
The Oriental Institute conservation staff, with the participation of the Getty post-graduate interns, undertook the next phase of the project. This involved creating mock-up RP system™ A-type storage chambers using metal coupons (silver, lead, copper and iron) as the test material. Prior to creation of the mock-up chambers, however, it was necessary to test each of the items to be placed in the chambers to ensure they would not adversely affect the condition of the test coupons and cause any alterations in the sealed environment. Five test chambers were set up each containing the four metal coupons and one component to be used in the mock-up RP system™ A-type storage chamber. Each test chamber was sealed in an Escal bag. The components tested were the hygrometer, the Escal bag itself, the glass dish in which the coupons were to be placed, the adhesive eye through which the oxygen analyzer pierces the chamber and the RP system™ A-type tablet. After six months, the coupons were removed from the test chamber and analyzed. None of the materials that are to be used in the mock-up RP system™ A-type storage chambers altered the test coupons during these tests. These results cleared the way for the creation of the actual mock-up RP system™ A-type storage chambers.
As the project progressed and more research was conducted by the conservation community, the focus of this study has evolved. The aim became the setting up of various modules that would allow for the long-term study of the effects of the RP system A-type on archaeological iron and the effectiveness of the system over time.
Many people were contacted, both in the conservation and science communities, and we thank all of them. A few of the generous people who shared their expertise and time with us were:
Shin Maekawa, The Getty Conservation Institute;
Vinod Daniel, Australian Museum;
Larry Tsuyuki, Mitsubishi Gas Chemical America, Inc.;
Mariam de la Cruz and Jeffrey Moore, Teledyne Electronic Technologies.
Additionally, we thank Mitsubishi Gas Chemical America, Inc. for generously donating their company's products to the project. And we thank Teledyne Electronic Technologies for working with us over several months and designing a new, affordable oxygen analyzer with a software modification that would give us improved resolution below 1%. We are very grateful to both of these companies and their representatives.