Stripped and metal damage repaired
Vitreous enamel is inlayed in the recesses and the piece is fired in a kiln to red heat, about 850 C. The surface blackening ( firescale so-called ) is a loosely-adhering mixture of copper and zinc oxides formed on the surface of the Gilding metal at this elevated temperature. Much of it can be removed by scrubbing under water but the tightly-adhering remainder must be dissolved by "pickling" the emblem in 10% sulphuric acid solution before further work can take place.
The emblem after pickling in 10% sulphuric acid solution and prior to "stoning", an abrasive operation which will grind the surface of the fired enamel level with the raised metal "cloisons" or cell walls.
The emblem after stoning and prior to the addition of more enamel to fill low areas ( seen below as darker, shiny spots ) after which it will be fired again.
After firing for the second time.
After pickling for the second time.
After second stoning and prior to the addition of more enamel to build up cells where the enamel is very thin. The thin spots are the bluish-looking areas in the black enamel and blackish-looking areas in the red enamel. The inlaying / firing / pickling / stoning sequence will be repeated several more times until a satisfactory enamel surface is achieved.
Restoration of previously-enameled emblems is a difficult operation. It takes considerably longer and requires more care and attention to detail to restore an emblem than it took to enamel it in the first place, mainly because of the severely reduced height of the cell walls - the cloisons - caused by stoning during the original enamelling.
After the final ( in this case 5th ) firing, pickling, polishing by hand and machine, and ultrasonic cleaning the emblem is ready for 18k gold plating.
Completed restoration, after 18k gold plating. ( In areas where the gold is highly polished the plating appears black. )
