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

DAVID & GOLIATH

GILDED AND SILVER IRON TILE “DAVID CHALLENGING GOLIATH”

AUTHORITY RESPONSIBLE OF THE RESTORATION: Museo  Stibbert, Opificio delle Pietre Dure - Florence

RESTORER:  Elisa Pucci

HISTORY:

Produced in a Milanese workshop in the 15th century, the 33 x 25 cm tile is made in embossed punched iron with gilded and silver damasking. Together with another tile belonging to the same manufacture and figurative cycle, the tile is kept in the collection of gilded small bronzes of the Stibbert Museum in Florence.  The complex technique is the same used as for the group of Italian parade armors belonging to the Mannerist period, comparable to a piece of goldsmith’s art for its detailed decorations. Most of the damasking in gold and silver, and in gold and silver alloy, shows severe state of decay, likely due to the environment and to human interventions.

 

LASER CLEANING METHODOLOGY

Laser cleaning has replaced the traditional restoration techniques such as piezoelectric ablation, micro sandblasting, scalpels, solvents, and chemical reagents, which have proven ineffective for some kinds of works of art. Lasers have allowed the accurate but gradual removal of the surface layers of decay (hydrated iron oxides and silver sulphide) mixed with residuals of decayed organic layers from previous coatings. A Q switched Nd:YAG (1064 nm) laser has been used, with fluences between 0.8 and 1 J/cm2, that avoid the risk of surface microfusion that the diagnosis had revealed. Pure Ethylic alcohol has been spread with a brush to save the iron support, immediately followed by laser irradiation.

To allow the thorough spallation of the decay, in particular of the silver sulphide, by nature very thick and adhering to the metal layer, three operational parameters have been devised, alternated to a mild manual finishing with scalpels and/or sharp tools to remove the firmest iron oxide blisters.  Laser ablation has proven extremely effective, and the comparatively low fluences have spared the extremely delicate surface due to the low adherence of the foil and their precarious state of preservation, especially the surface texture with the gold and silver foil still showing manufacturing marks under a microscope. It has also allowed the consolidation of the iron surface after a 10-micron deep thermic intervention, greatly reducing operation times.