Refiners and buyers use various methods to assay precious metals. Each method uses specific equipment, training, and cost structure which produces different standards of precision and reliability. Glines & Rhodes primarily uses the fire assay method for determining gold and silver content because it is generally regarded as the standard for superior accuracy. Fire assaying is not as fast and cheap as other methods, but the extra precision results in higher net returns for customers.
The fire assay process, or “cupellation,” is actually a miniaturized version of purifying gold. Fire assaying melts off base metal alloys like lead, copper & zinc and produces 24 karat fine gold. The weight of the pure gold sponge recovered is precisely measured against the weight of the sample going into the process. Fire assay is capable of precision down to 2-3 parts in 10,000.
We have made the heavy investment in equipment and training to be experts in ICP (Inductively Coupled Plasma) analysis. Our laboratory technicians use ICP to determine your platinum group metal content with excellent precision to a level of parts per million. This level of accuracy allows us to determine the percentage composition of even the smallest traces of metals present, including elements above sodium in the Periodic Table of Elements.
ICP uses an extremely high-temperature plasma source that vaporizes and ionizes atoms in a sample. This plasma temperature may reach 12,000°-14,000° F. Each atom or molecule present emits a different light wave that can be precisely measured and analyzed to provide the overall percentage composition.
X-Ray Fluorescence (XRF) is a fast and less expensive alternative to measure metal composition. Since metals are generally so dense in nature, only the surface material can be measured.
Glines & Rhodes uses XRF only when a quick and non-destructive estimate is needed. XRF is not regarded as being as accurate as fire assay or ICP, so Glines & Rhodes does not use it to settle on refining lots.