For jewelry that will rest against the wearer's skin, it is recommended that copper or copper based alloy's not be used with certain other base metals like gold and silver. This is because of the slight electrical difference between copper (also nickel) and other metals. This electrical potential will cause corrosion of the copper in the presence of an electrolyte such as sweat.
There are, however, many viable combinations of copper based alloys with more precious metals as long as they are used in other types of pieces. As an example of a safe use of copper in mokume, the container pictured below uses copper and silver mokume for the pull on the lid. In this case, the copper will not corrode even in combination with silver because it is not consistently exposed to an electrolyte.
Below is an example of a piece that does contain a corrosive combination. This is done primarily as an example of pattern in mokume. Of course, a piece like this can be sold, but only with the full understanding of the client that certain skin types may corrode the copper in the piece more quickly than others.
