Laser cleaning of metallic threads of a 15th century Italian velvet liturgical vestment

Cleaning of metallic threads has been a recurrent issue in historical textile conservation. A specific choice of the restoration methods is in fact required because the decayed metallic threads are wrapped around natural textile fibers. The conservation study of a silk velvet cope that presents different types of metal threads, argument of the French fellowship at the Accademia di Francia in Rome, has been an opportunity to test different cleaning methods, by including the laser ablation, besides the use of specific technologies to verify the effectiveness of the procedures. Applying the laser cleaning method [1, 2] to textile artifacts is used in Italy but is not very common in France, so the use of laser instruments for this specific application has been evaluated instead. Two laser instruments with variable wavelengths and pulse length have been tested: laser Nd:YAG (QS, 8 ns) with two different wavelengths (1064 nm and 532 nm) and the laser Nd:YAG (LQS, 120 ns), with a wavelength of 1064 nm. In particular, the silk velvet cope, dating from the 15th century, coming from the collection of the Musée des Tissus de Lyon in France, is enriched by three types of wires with different shape, composition and degradation state. The tested lasers have been used on the metallic fringes and the embroidered collar of the velvet cope. Parameters such as frequency, pulse, and beam size have been adjusted to match the small size of the metal strips and to avoid any damages to the silk fibers on which they are wrapped. The cleaning levels of the metallic threads have been evaluated through the SEM-EDS methodology, as well as the eventual damages of the organic fibers. Even if the whole research program is in progress, the preliminary results about the laser application are very encouraging. The final purpose will be to open a useful discussion about employing laser cleaning methods in the field of textile conservation in Italy and in France.