Micro-Raman and stratigraphic studies of the paintings on the Cembalo model musical instrument (A.D. 1650) and laser-induced degradation of the detected pigments

Micro-fragments of the painted part of the 'Cembalo' model by Michele Todini (1625-1689) are investigated. The technique used for painting the terracotta base was studied via the stratigraphic analyses. No background layer of inorganic materials, e.g. gypsum, was found. To prevent absorption effects due to the terracotta porosity, a very thin layer of proteinaceous material was probably used. The micro-Raman analyses have revealed the use of pigments currently used in the post-Renaissance period (lead white, indigo, yellow of iron hydroxide, gypsum, hematite and carbon black) mixed with a pigment, the Prussian blue, discovered in A.D. 1704. This raises the authenticity problem of the work of art, a problem analysed and discussed in presenting the history of the work of art, and after the pigment study. The presence of degraded lead white is recognized via the laser-induced degradation of the irradiated material. The possibility of a restoring action of the painted parts, as opposite to the non-originality of the work, is considered and discussed. Since most part of the investigated pigments shows laser-induced effects, a careful study of this phenomenon is performed by using the modern counterparts of the ancient pigments. For different laser powers, the temperatures of the investigated zones have been obtained via the detailed balance principle and connected to the laser-induced degradation effects. Copyright © 2007 John Wiley & Sons, Ltd.