Why do you need a hard flux? Your flux coat is laid down first on the metal of your choice. You want a hard flux which means it will not become fluid as quickly as you color layers that are applies later. This is specially important when using warm colors.
As in this pendant, of cloisonne it will be a deep layering of colors I need an enamel base flux that will hold up for many firings. Bovano 3# is a hardest firing leaded flux I have found for silver. This will protect my warm colors from mingling with the base metal and turning the enamels the color of mud.