Silver ornaments and jewelries easily change color if exposed to the air for a long time. Why? As isrevealed by nature of laws, all substances are instable in the state of high energy after absorbingenergy, this is scientifically called Thermodynamics Instability. Therefore, metal can spontaneouslygive out energy to return to the primordial stable ore state. For example, silver is available byheating Ag2S. So if silver meets sulfureted hydrogen gas or sulfur hydronium, the following chemicalreaction may occur: 4Ag2H2SO2=2Ag2S 2H2O. As a result, on the surface a substance called silver sulfideappears. Since the silver sulfide looks black, more and more silver sulfide appears when the reactionintensifies, thus the silver gets gradually from white to yellow, then grey and finally black.