TECHNOLOGICAL ANSWERS
TO RESTORATION

The growing need to preserve our cultural heritage is causing a rise in the demand for increasingly accurate cleaning techniques, featuring high selectivity and low impact.

CASI DI STUDIO

SILVER CHURCH FURNISHINGS COMING FROM THE BASILICA MARIA SS. DELLE GRAZIE

SILVER CHURCH FURNISHINGS FROM THE BASILICA MARIA  SS. DELLE GRAZIE – S. GIOVANNI VALDARNO (FLORENCE)

RESTORER:  Paolo Belluzzo

Edited from the article “Laser cleaning of silver artifacts” P.Belluzzo, S.Siano, G. Pieri, G. Lanterna, C. Innocenti, in Kermes, La rivista del restauro,  special issue of the restoration magazine, 2008, Laser cleaning of gold and silver gilded bronze.

 

HISTORY

The furnishings from the Basilica Maria SS. Delle Grazie in San Giovanni Valdarno (Arezzo) date back to the semi-industrial manufacturing of the 18th and 19th centuries. 

 

 

LASER CLEANING METHODOLOGY:

The early diagnosis investigated the metallic alloy and the decay products through X-ray fluorescence (XRF) and Energy-dispersive X-ray spectroscopy (EDS) linked to a scanning electron microscope (SEM). The oldest pieces were all make of a silver-copper alloy with silver over 90%, while the late 19th century pieces showed a larger amount of copper. The cleaning laser was a Long Q switched (EOS 1000 LQS) with pulse duration of 120n, power 130mJ and fluence between 0.5 and 1 J/cm2 to avoid fusion that may occur at higher fluences. Several tests confirmed that a slight damping, with brush or nebulizer, avoids side effects of redox and redeposition seriously jeopardizing the final outcome. Laser cleaning proved extremely effective in terms of time, since just a few pulses remove successfully the surface incrustations. The ablation is self-terminating: the removal process stops automatically when the highly-reflective metal surface is reached. In some cases, the surface showed a yellowish hue right after the laser treatment due to oxidation and redeposition. The problem was notably reduced when the laser treatment was complemented with a spray of argon. In any case, the yellowish hue is easily removed with a finger or a brush or a swab soaked in water or other solvent. The most effective methodology turned out to be for the laser treatment of small areas immediately followed by the hand finishing to remove the yellowish hue.

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