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

Cleaning of metallic threads has been a recurrent dilemma in historical textile conservation. Careful selection of restoration methods is in fact required because decayed metallic threads are wrapped around natural textile fibers. This article synthesizes the results of a conservation study undertaken at the Accademia di Francia in Rome of a silk velvet cope. The artefact, a silk velvet cope with different types of metallic threads, dating from the 15th century, coming from the collection of the Musée des Tissus de Lyon in France, was the subject of experimental cleaning tests using laser ablation and other technologies to ascertain the most effective method of cleaning compound textiles. Two laser instruments with variable wavelengths and pulse length were tested: laser Nd:YAG, QS at 1064 and 532 nm, and the laser Nd:YAG, LQS at 1064 nm. The laser tests were focused on the cope's metallic fringes, presenting three types of wires of different shape, composition and state of degradation. Parameters such as frequency, pulse, and beam size were adjusted to match the small size of the metal strips and to avoid any damage to the silk fibers over which they are wrapped. The effectiveness of the cleaning levels of the metallic threads have been evaluated through SEM-EDS, as well as the evidence of any damage to the organic fibers.