Original Paper

Analytical and Bioanalytical Chemistry

, Volume 399, Issue 9, pp 3041-3052

First online:

SR-XRD and SR-FTIR study of the alteration of silver foils in medieval paintings

  • Nati SalvadóAffiliated withDpt. d’Enginyeria Química. EPSEVG, Universitat Politècnica de Catalunya Email author 
  • , Salvador ButíAffiliated withDpt. d’Enginyeria Química. EPSEVG, Universitat Politècnica de Catalunya
  • , Ana LabradorAffiliated withBM16-CRG Consorci Laboratori de Llum Sincrotró (LLS) c/o ESRF
  • , Gianfelice CinqueAffiliated withDiamond Light Source
  • , Hermann EmerichAffiliated withBM01-ESRF
  • , Trinitat PradellAffiliated withDpt. Física i Enginyeria Nuclear, ESAB, Universitat Politècnica de Catalunya

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Altarpieces and polychrome carved wood from the fifteenth century AD usually exhibit golden and silvery areas by the application of a very thin foil of metal. The metal foils were normally protected from the atmosphere by a varnish or resin which maybe either preserved or absent. Moreover, they were glued to the background surface by adhesive substances (egg yolk, drying oil or animal glue). The high proportion of the glueing substances often renders the development of reaction compounds. With time, silver alters blacken or simply disappear completely. In this paper, we study the alterations to metal foils from a selection of fifteenth century artworks showing different glueing agents, organic coatings and several degrees of conservation of the organic coatings and metal leafs. The submillimetric layered structure and the high variability and low amount of most of the compounds present in the different layers, as well as their differing nature (organic and inorganic) make the use of micron-sensitive high-resolution techniques essential for their study. In particular, the high resolution, high brilliance and small footprint renders synchrotron radiation most adequate for their study. SR-XRD was performed to identify the reaction compounds formed in the different layers; μFTIR was used at to identify the silver protecting organic coatings, the metal foil glueing layers and the corresponding reaction compounds. The results obtained suggest that atmospheric corrosion is the dominant mechanism, and therefore that the degree of corrosion of the metal foils is mainly related to the conservation state of the protecting coatings.


Sampling point, MO image from surface of the sample and SEM image from polish cross-section of the sample


Silver foil Silver chloride Silver sulphide Cultural heritage XRD FTIR