Silver-topped gold was an innovation by English jeweler James Cox, c. 1767 - the middle of the Georgian Era - which allowed silver to be backed by gold. Prior to this, gems being set in white metal were set in silver only. If the jewelry was not cleaned constantly, silver tarnish, rubbing directly onto skin, could leave marks or stain fabric. Gold does not oxidize and therefore leaves no discoloration on skin or clothing. Since the use of white metal was desirable for gem mounting, silver remained in use for jewelry with the addition of the gold backing. This process continued to be popular until the late eighteenth century. As the technology was developed to make it possible to use platinum in jewelry, it too was added to the top of yellow gold in the same manner as silver. Eventually, the gold backing was eliminated and jewelry made purely of platinum took its place.