Why do silver artefacts tarnish? Considerations on the phenomenon for its better understanding and potential prevention.

Abstract

Silver, because of its white coloration and intense brightness, is a metal universally considered beautiful. This particularity of aesthetic character is due to physical, chemical and mechanical properties that have, millennially, conferred it a great value and eclecticism in terms of application. It is desired by multiple sectors of society, increasingly by electronics. All of them knowing that, when exposed to the air, it tends to alter, tarnishing and leading to multiple problems of various kinds. When within the cultural sector, in museological indoor environments with preservation obligations, it is expected that its alteration will not occur. However, although it tends to be slower and smaller in scale, but not always, the tarnishing process continues to occur even there, fitting into the complex and comprehensive universe of atmospheric corrosion. In the sense of sharing information that may allow a better understanding on how the process occurs, leading to the tarnishing of artefacts both in storage and exhibition context, the problem is presented and discussed, retro prospecting it, presenting forms of manifestation and discussing the categorization of the type of corrosion. Notions of the chemistry of atmospheric corrosion are introduced, relating them to the presence and properties of water. The results of an extensive bibliographical review of the contributions of specialists from various disciplinary areas are presented in a very summarised and selected way to clarify the phenomenon, covering both the fundamental and applied points of view related to different agents, their interactions with silver and its consequences, so as to provide heritage/museum professionals useful and expeditious information on the task of managing, in an integrated way, the risk of damage and preventive conservation.