Desiccated Microclimates for Heritage Metals: Creation and Management

Abstract

ABSTRACT Since the early 1970s, archaeologists, conservators, and curators have turned to published guidance for methods of safeguarding archaeological metals in the short and long term. Much of this has appeared in editions of the ubiquitous handbook First Aid for Finds, the most recent of which dates to 1998. A central message across all guidance has been to dry metals post-excavation and prevent their corrosion during storage by desiccating the environment around them. This has been proven crucial for iron, with reports of catastrophic loss of collections arising from inappropriate storage environments. There has long been agreement that an effective, low cost option for desiccation is the packing of artefacts in boxes with a desiccant. Though advice on the details of how to achieve this has evolved over time, what has not changed is the lack of quantified evidence for the methods proposed. Informed by a survey of current practice in the sector, this study investigated quantitatively the many variables involved in creating desiccated microclimates for storage of heritage metals. This paper presents the results of an evaluation of the airtightness of a range of commercially available boxes, the optimum mass of desiccant, the effect of external environments, and preliminary data on the efficiency and risk of drying damp objects with silica gel. A second paper will report the effect of stacking boxes on their airtightness and present data on the accuracy and long-term reliability of humidity indicator cards. The guidance arising from laboratory testing of the hardware and methods for desiccated storage is designed to be achievable and adaptable. Combining these findings with corrosion rate data for iron artefacts allows the escalation of risk to objects from decisions in the storage process to be calculated. Together, these papers offer an evidence-based and practice-focused update to First Aid for Finds.