Investigation of surface patinae on religious marble artefacts

Abstract

Religious marble sculptures and architectural elements are often characterised by surface layers used as protective coating and aesthetic finishing, originally applied by the artist or subsequently on the occasion of restoration works. This paper focuses the attention on some cases studies specifically referred to religious marble objects with different kinds of coating: the bust of the Pope Innocenzo X, dated back to the 17th century and attributed to the master Algardi, the 12th capital of Magister Giulelmus, the 15th century baptismal font made by Francesco d’Ancona in 1471 and the two bas-reliefs, representing respectively Saint Michael the Archangel and Saint Raphael the Archangel, attributed to Agostino di Duccio, dated back to 15th century. In all cases surface layers can be observed on the marble that constitutes the sculptures and the objects. These layers were sampled and investigated through laboratory techniques, specifically X-ray fluorescence spectroscopy, Fourier transform infrared spectroscopy and optical microscopy in order to characterize the composition and establish if they are original finishing or restoration materials