Here in England, whilst it would not be illegal to use gold on the front
and silver on the back, it could only be marked as the lesser value metal,
that is to say it could only be legally described as silver. All
jewellery here has to be hallmarked, which means it is sent to an official
assay office, tested and stamped, so there is no way round it, if you are
doing it professionaly.
Kevin Eva, Northern England, UK