When freshly deposited, it is the best reflector of visible light known, but is rapidly tarnishes and loses much of its reflectance. It is a poor reflector of ultraviolet. Silver iodide is used in seeding clouds to produce rain. Silvet nitrate, or lunar caustic, the most important silver compound, is used extensively in photography. While silver itself is not considered to be toxic, most of its salts are poisonous.
Natural silver contains two stable isotopes.
Forty nine other radioactive isotopes and isomers are known. Silver compounds can be absorbed in the circulatory system and reduced silver deposited in the various tissues of the body. A condition, known as argyria, results, with a greyish pigmentation of the skin and mucous membranes. Silver has germicidal effects and kills many lower organisms effectively without harm to higher animals. Silver for centuries has been used traditionally for coinage by many countries of the world.