THE REMOVAL OF CORROSION PRODUCTS ON EXCAVATED METAL ARTIFACTS USING CHELATING AGENT

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1. Selection of Chelating agentWe had first compared EDTA-3Na and NTA-2Na on the market of wide use. Both solution are almost neutral and have the same effect of removing corrosion products on copper alloy objects. We chose EDTA-3Na, because the solution of NTA-2Na slightly stimulated the skin, and continued our study.2. Removal of chelating agent from treated objectsAfter several time of washing with standing and flowing distillled water, the agent was not detectable by ultra-violet spectroscopy. But in a few cases new corrosion products appeared on the treated surface. We thought they were changed sensitive by the treatment and tried to stabilize the corrosion.3. Adequate quantity of chelating agentDuring treatment, we measured solution within the measurement limits by UV spectroscopy showed the degree of reaction. When the solution was regulated to react 0.3 to 0.5 mol of copper ion per mol of EDTA-3Na, we treated them quickly and economically.4. Stabilization of the surface of treated objects.Generally most of new corrosion products on the bronze objects treated by chelating agent are stabilized by benzotriazole (BTA).In case that it should not work, we examined the objects impregnated and coated with fluorolefin acryl copolymer under high humidity conditions. This resin has high effectiveness to shut off oxygen and vapor, and yet is easily solved by solvent after treatment.5. Removal of corrosion products from iron objects.We applied above agent to iron objects. The layr of corrosion products which is already fragile is easily removed by mechanical methods. Chelating agent does not help much than the usual mechanical removal methods.