The melting time will depend on crucible size, and amount of contents. Temp should be around 2000 F, maybe 50 degrees higher. Contents should be bone dry. Foaming is the release of CO2 evaporating off due to the heat reaction. Try using Sodium Hydroxide flakes for less boiling reaction. Litharge is far superior to metallic Lead for a collector. The amount of Silica needed, if any, will be determined by the erosion of the crucible. Not enough Silica, and it will eat the crucible, leading to spills. Some assay books will give the exact equation for concocting the correct flux. A knowledge of minerals and chemistry is required, otherwise you are at the approximation game of trial and error. Concentrates will change your recipe for the flux. If you go too heavy on the Soda Ash, it will eat the crucible. Read, then re read Bugbee some more. It takes a while for the chemistry of each flux, and the respective reactions, with each mineral in the sample.
