Europium Elements Coin in Glass Capsule
Europium's natural color is a rather dark steel-gray. The metal is chemically reactive, and within minutes of being exposed to air, it will start to tarnish. When it is vacuum-sealed in a glass capsule, it immediately starts to turn color, going from a light green to blue. The luster of the original coin is still present. We tested several methods to try to prevent the coloring from happening - the best result so far is a light to moderate green color.
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