Thanks for the reply. I researched some of the cloisonne asian vases, but could not find anything quite like this one. There is no indication that there is any loss of the enameled surface across the piece. It is clearly a design element to have the decorated design raised in relief above the undecorated metal. If cleaned, the contrast would be even greater, but the lustre of the undecorated metal below the raised and enameled pattern has dulled over time. The design elements appear intentional and uniform in this case.