Pyrite oxidation: a history of treatments at the Natural History Museum, London

Whilst surveying the palaeontology collections at the Natural History Museum London (NHM), a team of Conservation Technicians working on 'Project Airless' (a re-storage project for actively deteriorating pyritic specimens) kept a record of specimen labels describing past methods for treating pyrite oxidation, ranging from 'boiling in common soda' to treating with 'Savlon'. This prompted further research into the thinking behind these approaches, and resulted in a historical review of treatments used at the NHM and how they compare to current methods. The oxidisation of unstable pyritic material became a prominent issue during the development of geological collections in the 19th Century, when early collectors provided most insight into best practice storage of affected specimens, although it was not until the 20th century when more intensive research was conducted and recommended treatments for deteriorating pyritic material began to circulate. Regardless of the treatment, however, once specimens were returned to storage conditions of high relative humidity (RH) the reaction would often recur; this instigated the need for a more preventative approach focussing on reducing, if not eliminating, the key agents involved in the oxidation process: oxygen and high RH. Project Airless is the latest attempt at the NHM to combat pyrite oxidation on a large scale by storing affected specimens in anoxic microenvironments to prevent further deterioration. Severely affected specimens are also exposed to ammonia vapour in a method which has evolved from earlier treatments. Although commonly referred to as The Natural History Museum London, the museum was officially known as The British Museum (Natural History) until 1992, so for the purposes of this article the 'BM(NH)' will be referred to until this date, and the 'NHM' thereafter.