In literature there are several studies of the application of vacuum plasma to the cleaning of works of art. Unfrotunately the use of vacuum plasma is limited by intrinsic factors: the size of the manufactured articles is limited to the volume of the vacuum chamber, the entire surface of the artifact is treated in a non-selective way, the process is expensive, but the most important limitation is the lack of control by the restorer.
The European project PANNA has made possible the creation of an atmospheric plasma device suited for cultural heritage. The peculiar characteristics of the Nadir Plasma Jet, in addition to not having the disadvantages of vacuum plasma, are the treatment temperature below 40°C, the dimensions suitable for manual use, the possibility of managing the jet in terms of power and of treatment speed, so that the plasma cleaning method is selective and gradual, and therefore controllable by the operator.
Within the PANNA project, different experimental studies have brought positive results for the restoration sector on multiple substrates and different types of degradation.
One of these studies aimed at the use of the Nadir Plasma Jet for the removal of organic material on stone substrate. Specifically, the plasma-assisted removal of epoxy resin (Araldite®) spread on Istrian stone and artificially aged was evaluated. The Plasma Jet was used punctually and in an oxidizing configuration: low concentrations of oxygen are added to the plasma support gas (argon), in order to speed up reactions to break the chemical bonds with atomic oxygen.
Characterization tests using infrared spectroscopy and contact profilometry have shown that the Plasma Jet is able to produce a cleaning spot with a diameter of 8 mm, completely removing an epoxy resin thickness of tens of micrometres.
An innovative cleaning method was therefore tested for the restoration sector, a non-contact method, which does not use solvents and does not produce waste due to cleaning, but sublimates the organic patinas into non-harmful volatile compounds, such as water and carbon dioxide.
