Pressure-induced valence change in samarium sulfide SmS is reminiscent of alchemy, for when the electronic transition has taken place, the originally dull looking substance glitters like gold. Although it is not the realization of the alchemist's dream in the true sense, the material in the new state exhibits extraordinarily interesting behavior. As a novel feature, the valence state of the samarium fluctuates between two electronic configurations at a very fast rate. The physical properties of systems containing lanthanoids can be profoundly altered by manipulating the valence state by pressure or by chemical substitution. These phenomena will be described and discussed in the present article.