There can be problems related to enamelling on some 18ct alloys - sometimes the enamel will not adhere properly and can leap off after the processes have been completed. If the ring is a casting and silicon has been added it is likely to cause trouble. if you are in US you should use alloys recommended by US enamellers and talk to the bullion suppliers. Generally if you are applying enamel around raised lettering, it will be given extra strength and reinforcement from the raised sections. If the ring has been rhodium plated before and you are re-enamelling you will need to remove the old rhodium which will discolour when you fire. Generally Rhodium Plating after the the enamelling is complete, is straightforward, although some opaque black enamels will become matt in acidic plating solutions. i would use Vitrum Signum PJE 610, but i daresay there is a suitable Thompson black which you may find easier to obtain.
I have been asked to enamel an 18K white gold ring. It is a simple infill around some lettering. I was wondering if anyone knows if there are any problems associated with the enamel and the subsequent rhodium plating? Are there any pointers that I need to know? Thanks!