Context

The second half of the twentieth century saw a boom in the scientific investigation of historical and cultural heritage materials. Faced with the need to conserve objects listed as historic monuments and works in public and private collections, characterization tools and methods entered a field previously reserved for synthetic materials or geological issues. Complementary observation and analysis methods are used to refine our knowledge of materials and processing techniques or, in some cases, for dating or authentication purposes. In addition, research programs are set up to understand the causes and mechanisms of deterioration observed on heritage objects, helping to define the best conservation conditions for works of art.

A recurring problem concerns the chromatic alteration of lead-based pigments. Red –– and lead white, in particular, are known to blacken...