I think they were completely hand engraved and than hand painted , I think factory craftsman did them. There is one Texas air pressure hand engraving machine manufacturer , they sell a laser printing paper which printed image can be transferred from transparent plastic to metal or plastic. They also sell engraving patterns for transfer to metal and than hand machine engraved.
But easiest and most stable merhod is to order laser engraving on to ivory. There are lots of laser engraving services which burns small dots and so the images on to glass to wood to metal and whatever you want. Result is excellent.
Another way is to order laser crafted hand stamps and use them and than for method 1 and 3 , coat them with clear polyurethane sprayed.
Good luck ,
Umut