An assay is an analysis designed to measure and test the composition in ore, alloys, and precious metals. With respect to precious metals, specifically silver and gold, it is a way to make sure that all the coins or bars produced in a mint meet the correct purity standards and content. For example, if a mint promises that a gold bar has 99.9 percent purity, an assay is necessary to make sure that all the gold minted in that lot meets those standards.
The practice of assaying was commonplace when gold and silver coins actually were used in circulation, as with the silver half-dollar. Although most countries, including the United States, no longer circulate full gold or silver coins for spending, the process is still important. For example, content purity is still essential in the creation of silver and gold bullion, coins, and special releases.
There are several assaying processes, depending on the type of metal or item being checked for purity. First, the assayer takes a sample, either by drilling into the metal for shavings or taking a sample while it is in a molten state before formation into a bar or coin. From there, assayers have some different options. All of the most common assaying processes are listed below:
Fire Assay – Fire assay is one of the oldest methods of checking the purity of content in precious metals. Gold and silver are both checked this way, with corresponding amounts of silver and gold used together in a cupel, or disposable crucible, which helps check the amount of non-precious or impure metals in a sample.
Dry Assaying – Dry assaying works for gold and silver, as well. Fluxes, which are chemical cleaning agents, get heated with the metals. This creates a combination of any impurities, and in turn, it creates a slag. During the process, the precious metals separate and the purest forms settle at the bottom. After the mixture cools down, the slag gets chipped away, leaving the metal to get weighed and compared.
Wet Assaying – In wet assaying, solvents dissolve the sample. This process leaves a solution that the assayer analyzes chemically. Depending on the metal or ore in question, assayers can use salts or electrolysis to separate it.
Spectrographic assaying requires the sample to actually emit light. This occurs when the assayer passes electrical discharge through the sample. Assayers look at the intensity and strength of the light emitted by the sample, allowing them to measure the sample’s metal content.
X-Ray Fluorescence Assaying – In X-ray fluorescence assaying, the metal actually emits X-rays. This requires irradiation by an X-ray beam. The assayer judges the metal depending on the intensity level of the X-rays it emits.
Other Assaying Methods – Typically, titration is the process used to assay silver. Cupellation is the process used to assay gold. With platinum, ICP OES, or inductively coupled plasma optical emission spectrometry, is the process used to test purity.
Because purity is essential in gold and silver coins or bullion, as well as in platinum and palladium pieces, assaying is likewise essential. The main reason for assaying precious metals is to make sure they meet the standards put forth by the mint, or the requirements necessary for a particular coin or bar. As in the Trial of the Pyx, which is a ceremonial process for assaying still used in the Royal Mint, the procedure goes far back in history. It tested not only purity, but also honesty.
Many gold and silver pieces come with some proof of assay. Smaller ounces, for example, may come sealed in an assay card, which includes such information as the date of creation or assay. An assay certificate, though different from a card, is similarly designed to provide proof of purity and authenticity. In both cases, buyers, investors, and collectors have proof that their purchases are both pure and worthwhile.
The information included on an assay is just as important as the presence of a card or certificate. The assay tells recipients the serial number of the piece, which is further proof of its authenticity and integrity. Good assay cards also include the specific type of metal, thus proving that it is pure silver, gold, palladium, or platinum. It proves the promised purity of a piece and includes the mark of the mint where the piece originated.
A certificate of authenticity, or COA, is somewhat like an assay certificate or card. It is usually a sticker or a seal on a proprietary item. Usually the seal is on a piece of paper or the actual certificate, and it proves that the coin or bullion is authentic. Unlike an assay, however, there typically is no thorough process to prove the item’s purity, or at least it does not go to such great lengths. Similarly, a COA does not seal a piece of gold or silver, unlike an assay card.
That being said, a COA does contain pertinent information like purity and a stamp of approval. It will generally include some sort of maker’s mark as well, along with information about its fineness and weight. Some products do not receive a COA for various reasons. They may come in bulk orders, or they may come with an assay, which can render a COA unnecessary.
Generally, bullion bars come with assay proof. This applies to gold and silver, of course, but bullion made of platinum and palladium typically come with an assay, as well. This is because bars are large, valuable, and promise high levels of purity. As such, special coins and limited editions come with an assay as well to prove their authenticity and value. This is not usually necessary with regular bullion coins, especially if they’re still somehow in circulation.
Limited edition coins and special releases come with a COA in most cases to prove their authenticity, as well. Since these are usually commemorative pieces, the proof of authenticity is important, but proof of purity isn’t always a high priority. That is why COAs typically apply to coins and unusual or special items but not bars.