Corrosion mechanisms in copper-based artifacts investigated by secondary ion mass spectrometry

In the field of ancient metallic objects belonging to the world of Cultural Heritage, copper-based artifacts represent the largest part of them. The pristine appearance of these objects as conceived by the artist or the craftsman is often concealed from our eyes due to the presence of surface corrosion patinas or crusts. This sort of extra layer can sometimes completely modify color and structure of the artwork. Therefore, understanding the formation mechanism of the corrosion layers is of fundamental importance to preserve and protect the good when it is made of copper or copper alloys. Secondary ion mass spectrometry is considered an emerging technique for the investigation of patina and crusts of corroded objects. The surface and in-depth chemistry of such complicated multilayer structures can be efficiently described with high depth (1 nm) and lateral (<50 nm) resolution by using SIMS and ToF-SIMS techniques. In this article, we summarize how information obtained from ion bombardment experiments such as the penetration profiles of reactive species, the stratigraphy of corrosion products, and the identification of emerging and surface-spalling species can improve the knowledge of the corrosion phenomena in copper-based artifacts.