If you are buying, selling, or
refining gold, you're going to want to be sure you're getting full value. One
way to do this is by assaying, or in other words, evaluating, the gold. This is
something often done by a precious
metals refinery, like Jewelers Refining Group. The basic process has been
around for hundreds of years but has evolved over time. The following are the
main ways gold is assayed today:
- Fire - This method is the oldest and most accurate, and also the most preferred. First, the gold is melted and a sample is taken and weighed. The sample is placed in a special crucible called a cupel. The cupel absorbs all non-precious metals and what remains is then hammered flat, rolled thin and heated in a porcelain crucible. A weak nitric acid solution is added, which removes any silver. The gold is rinsed with distilled water and dried. What remains is 99.999 percent pure gold. This sample is weighed. The weight of the original sample is divided by the weight of the pure sample and the result is the assay.
- Inductively Coupled Plasma Optical Emissions Spectroscopy (ICP-OES) - Solid samples are dissolved, mixed with water and fed into plasma. The plasma will emit light on a particular wavelength indicating gold. The light is recorded and calibrated against specific standards. This provides a quantitative analysis.
- X-Ray Fluorescence (XRF) - This is similar to ICP-OES but can be done on samples that are solid, liquid, or powdered. The sample is irradiated with x-rays and the individual component wavelengths of the fluorescent emissions are measured by the spectrometer.
There are also methods you can
use at home with ingredients you probably have on hand. For instance, to detect
gold-filled items (gold plated vs. copper), simply etch a small scratch and
apply nitric acid. The copper will react and bubble green. While these methods
work, it's important to always get an assay performed by a professional,
qualified company.
