Hydrogen cold plasma reduction in a restoration-conservation protocol for metallic archaeological heritage

In this work, hydrogen cold plasma has been used to restore metallic archaeological objects. The study has been carried out working with real metallic archaeological pieces (some coins which belong to the archives of Santa Caterina 68/99,1105 sector A, in Barcelona), and with samples of different materials as copper, brass, steel and lead, rusted artificially by three methods (high temperature, oxygen cold plasma and saline solution) and different exposition times. This technique is capable to remove oxides, chlorides and other corrosion salts easily of several pieces at the same time, and coupled with mechanical treatment, it reduces dramatically the restoration time. Furthermore, this treatment is advantageous due to the creation of surface porosities caused by a selective reduction of the identified oxides and compounds of the different metallic samples studied. After the treatment, samples are kept inside polymeric bags in the absence of humidity and oxygen. For a short period of time, this procedure is sufficient to prevent and the decrease the surface reactivity of the treated samples. The residual oxygen within the bag, is enough to stabilise the surface and keep the samples protected from external atmospheric agents.