Specifications Fire assay fluxes according to customers' recipe, or our own specification. Gold free and silver free type are available The famous fire assay has been around for more than 500 years, but it still is the best method for determining the quantity of gold, platinium and other precious metals, thus widely used by gochemical assay laboratories. The fire assay process works by fusing or dissolving the rock sample in a crucible using a lead glass flux. Fluxes of various types are used on various types of ores. Most flux mixes may contain the following: Litharge, Sodium bicarbonate, Silica, Borax, Flour, Florite, Etc. Gemhold does custom manufacturing of lead monoxide(litharge) with qualified manufacturer in china, producing top grades of litharge from 99.5% - 99.9%min, which are widely used in fire assay, optical glass, piezo ceramic, and other industries. For fire assay industry, gemhold can produce assay grade litharge with very low gold and silver content, say, gold less than 1.5ppb, and silver less than 0.15ppm. Gemhold can produce assay fluxes according to customers' recipe, or from our own standard. Our ability to product high quality litharge enable us to produce idea fluxes needed in the low level assay works. Our quality control system and semi-automatic manufacturing processes make our fluxes fully reliable. We can assay each batch of our flux if customers require that, and coa be be provided before despatching