... , Mohs hardness 3-4, dielectric constant 18.10, insoluble in water, soluble in acid, ammonia, ammonium chloride, dissolved in sodium hydroxide ... color solution, which leads to hydrogen or carbon monoxide at high temperature can be reduced to metallic copper. Mainly used for ... ---Acid insoluble ≤%0.010.20.2Cl¯ ≤%0.010.20.2 High quality black copper oxide plating grade