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Monday, October 6, 2008: 3:35 PM
Virginia City III (Flamingo Las Vegas)
Silver Artifacts Protection by Anticorrosive Coatings
Venice Gouda1, Nabil Abdel Ghany1, Ahmed Awad1, Jelica Novacovic2and Panayota Vassiliou2
1.National Research Center , Dokki, Cairo, Egypt.
2. School of Chemical Engineering, National Technical University of Athens ,9, Iroon Polytechniou Str, Zografou 157 80, Athens, Greece
Many objects of cultural heritage constituted of bulk or plated silver or alloys are often displayed in museum show-cases or are kept in depositories. Silver artifacts are subjected to tarnish with time by the reaction with atmospheric pollutant elements, namely sulfides, forming silver sulfide. The blackish films thus formed make these artifacts inappropriate to display and have to be dealt with. Tarnish can be removed with a silver polish, by a chemical dip , an electrochemical reduction method. or galvanic coupling with aluminum Several methods have been developed to reduce silver tarnish such as silver alloying, surface treatment and coatings. The protection system employed has to follow the Venice Charter, to be removable and not to change the aesthetics of the object to be protected. In this study, silver alloys have been tested for corrosion under accelerated corrosion conditions. A system of hexadecane-thiol in the range of 0.1M-0.3M has been tested on silver coupons. Paraloid B-72 polymer has also been used as the organic vehicle for dispersed nano-pigment of aluminum oxide. Several percentages of pigments have been tried to check on the system capabilities, without altering the visual effects of the surface. The different protection systems has been prepared and either brushed on the surface of the silver coupons or the silver coupons were immersed in the protection system. Accelerated immersion testing in sulfide solution has been tried on the coupons. Electrochemical testing, visual observations and gloss measurements showed that the protection with 2% nano-Al2O3 and the hexadecane-thiol exhibit better protective properties than the plain Paraloid.
Key words: silver, artifacts, protection system, Hexadecanethiol, Nano-pigmented alumina.
Venice Gouda1, Nabil Abdel Ghany1, Ahmed Awad1, Jelica Novacovic2and Panayota Vassiliou2
1.
Many objects of cultural heritage constituted of bulk or plated silver or alloys are often displayed in museum show-cases or are kept in depositories. Silver artifacts are subjected to tarnish with time by the reaction with atmospheric pollutant elements, namely sulfides, forming silver sulfide. The blackish films thus formed make these artifacts inappropriate to display and have to be dealt with. Tarnish can be removed with a silver polish, by a chemical dip , an electrochemical reduction method. or galvanic coupling with aluminum Several methods have been developed to reduce silver tarnish such as silver alloying, surface treatment and coatings. The protection system employed has to follow the Venice Charter, to be removable and not to change the aesthetics of the object to be protected. In this study, silver alloys have been tested for corrosion under accelerated corrosion conditions. A system of hexadecane-thiol in the range of 0.1M-0.3M has been tested on silver coupons. Paraloid B-72 polymer has also been used as the organic vehicle for dispersed nano-pigment of aluminum oxide. Several percentages of pigments have been tried to check on the system capabilities, without altering the visual effects of the surface. The different protection systems has been prepared and either brushed on the surface of the silver coupons or the silver coupons were immersed in the protection system. Accelerated immersion testing in sulfide solution has been tried on the coupons. Electrochemical testing, visual observations and gloss measurements showed that the protection with 2% nano-Al2O3 and the hexadecane-thiol exhibit better protective properties than the plain Paraloid.
Key words: silver, artifacts, protection system, Hexadecanethiol, Nano-pigmented alumina.