Assaying is the process of testing scrap for its precious metal content. While it is sometimes possible to look at a sample and guess its possibilities, more often than not, to get an accurate idea of something's value, it must be analyzed.
Fire Assaying Gold Extraction, also known as Gold Assaying is accomplished using a process known as “Fire Assay” which is the oldest known method of gold and silver assay and continues to be one of the most accurate.
Once the gold scrap is melted, a sample is taken in a molten state and precisely weighed and recorded. The sample is wrapped in assay lead foil along with a quantity of pure silver and placed in the furnace.
All non-precious metals are absorbed by the hot cupel and the precious metals form a button within the cupel. The cupel is removed from the furnace, hammered flat, rolled thin and then heated in a porcelain crucible containing a weak nitric acid solution that removes the silver. The gold is then rinsed in distilled water to remove any residual acid and then dried.
A secondary step used for platinum and palladium is called ICP or Inductive Coupled Plasma.