Bureau Veritas provides fire assays through its global laboratory network.
Fire assay is a vital aspect of determining the precious metal content of samples. There are a number of stages in the process from the original sample to isolated precious materials which can be tested using other techniques. Samples are placed in crucibles and heated to more than 1000°C with other compounds including lead oxide. The sample separates into metals mixed with the lead and covered molten glass (slag), which contains base materials and other contaminants. This is separated from the lead ‘button’ by cupellation. The lead ‘button’ is placed on a cupel and heated to more than 1000°C.
The cupel absorbs the lead leaving a small amount of precious metal which can then analysed in a variety of ways – through chemical means, through gravimetric testing or by spectrometer.