Preliminary study for the evaluation of a pulsed coaxial plasma gun for removal of iron rust stain from bone artifacts

Abstract

• Iron stain is one of the most crucial aspects of archaeological bone deterioration. • Chemical reaction between bones and the iron stain was explained. • The coaxial plasma cleaning was used for the first time for removal of iron stain. • The efficiency of plasma cleaning depended on power, numbers of pulses, and etc. • Analytical methods were utilized for the evaluation of the coaxial plasma cleaning. The pulsed coaxial plasma gun is an effective and fast way to remove stains found on the surface of cultural heritage materials. Invisible oil films, dust deposition, corrosion products, or other contaminants can be cleaned by plasma. Iron stain can be found on bone when it is in direct contact with the corroded iron object or in proximity to the corrosion products in the soil. This study aims to evaluate the removal of iron stain from the surface of bone by using Pulsed coaxial plasma. Different parameters of pulsed plasma have been evaluated to reach the best condition of the treatment. Pulsed coaxial plasma was applied to modern bone samples artificially stained with ferric hydroxides. Analytical techniques used to evaluate the iron stain removal were digital microscope, SEM-EDX, FTIR, color measurement by UV spectrophotometer, AFM, pH value, and contact angle measurement. The results indicated that the coaxial plasma is highly effective for iron stain removal and does not affect treated bones. The best cleaning was performed by pulsed argon plasma at 50 pulses, pressure of 0.2 mbar, 0.5 cm distance, and 3kV plasma power.