Did you want someone to engrave something into your dies, so that the engraving would transfer to a piece of gold or silver when the die was used? That would be a stamping operation; engraving is done directly onto the precious metal. Dies are typically used for punching out shapes; if you wanted to put a raised or lowered design into the precious metal sheet, that would require a stamp. Engraving is normally quite a bit shallower than 6mm as well.