It is a fumigated silver leaf with sulfur that discolor into BLUE by the sulfurization reaction. Silver is discolored into red, blue, and black by smoking in sulfur. The technique of smoking the silver leaf by sulfur is originally developed in Japan. It is a very special skill that can be done by limited craftsmen. Because each leaf’s expression is different and not possible to produce the exact same color, there is a feature that you can actually enjoy this as a pattern.