Unstable historic glass: symptoms, causes, mechanisms and conservation

Abstract

A significant proportion of glass objects in museum collections are known to be actively deteriorating, irrespective of the storage or display conditions. Various terms have been used to describe the effect including sick glass, glass disease, glass illness, crizzling and weeping. The symptoms reflect the chemical instability of certain types of glass as a consequence of their manufacturing technology, such as over-purification of raw materials or poor batch formulation. A review of the literature indicates the wide range of approaches adopted to mitigate the problem. There are significant discrepancies between those that have been recommended in the past and those in the current conservation literature, indicating the need for further research.