When it comes to gold assay, there is no question that true fire assay is the most effective and accurate method. What is the history of true fire assay, and what makes it so accurate?
Gold fire assaying, or cupellation, is a method of determining the purity of a piece of gold alloy or ore. It is a method gold refiners have used for thousands of years. Archeologists have found artifacts in ancient ruins that refer to fire assaying, and the Bible even mentions it. There are references to assaying in literature from the 1100s, and of course, we continue to practice it today.
Surprisingly though, for most of the history of modern metallurgy, true fire assaying has not been the most popular method of gold refining. The traditional method has been something known as the touchstone method, which involves rubbing the item on a touchstone and testing the stone by treating it with certain acids and examining the color. This method is accurate to 10 to 20 parts per thousand.
The touchstone method has been largely replaced in the modern world by a technique called X-ray fluorescence. Some refiners prefer this technique because it does not destroy any of the ore/alloy and still delivers accuracy of two to five parts per thousand. It works by melting and stirring the material so the content is evenly distributed throughout, and then analyzing a sample from the center with X-ray fluorescence spectroscopy.
There is no dispute that true fire assay is the most accurate method of refining gold. We can also use it on white gold, which will not work on touchstone, and on electroplated materials, which will not work for X-ray fluorescence. Some refiners prefer to stay away from this method because it is a much more involved process than other methods that involve superheating the material in a fire assay furnace. However, if accuracy is your priority, there is no alternative.
At Pease & Curren, we understand you deserve the greatest possible accuracy in your gold refining process, which is why we always use true fire assay so you get fair value when it comes to gold scrap. With over 100 years of experience in the industry and an unparalleled reputation for honesty, you know Pease & Curren is the name you can trust when it comes to a gold refiner. If you have any questions about fire assay, gold purity testing or Pease & Curren, or would like to engage our services, please contact us today.