The fire assay process has been well known since ancient times as a method for measuring the gold content of precious alloys. In fact, it was first mentioned by the Egyptians on a cuneiform tablet that dates back to about 1360 B.C. Even now, it is still the most accurate and precise method, besides being the most popular in the goldsmith’s field. This notwithstanding, very little information is available about the microstructural evolution of the specimen undergoing the different steps of the process. The present work is aimed at describing such an evolution by means of optical and electron microscopy as well as other analytical techniques. The performed observations reveal some unexpected microstructural changes that cast new light on the whole process and allow for understanding the remarkable effectiveness of the method. Knowing why each step of a procedure is performed also helps the operator to avoid making mistakes.

Author(s): Paolo Battaini