Assay or Certificate of Authenticity? What’s the difference

Assay or Certificate of Authenticity? What’s the difference?

Assaying was a common practice when silver and gold coins, like the renowned silver half-dollar, used to be in circulation. Most countries, including the US, do not circulate full silver or gold coins for regular spending, yet the assay process is still essential in the creation of their precious metal bullion. When investing or collecting precious metals, you probably noticed that some of them come in assay cards, with assays or accompanied by certificates of authenticity. If you are still wondering what’s the difference between these two, this article will help you find out their meanings so you can make thoughtful decisions when purchasing precious metal bullion.

What is an Assay?

The definition of assaying in the precious metal industry has two meanings. An assay is basically a test procedure of analyzing and measuring the fineness of a metal by testing its composition in alloys, precious metals, and ores. It is an essential process in determining the amount of precious metal in a mineral deposit. The assayers provide the assay’s results and grades to map and use them for evaluating future drilling operations and potential deposits that can be explored. When speaking about precious metals, like gold, silver, or platinum, the term assay also refers to the way of ensuring that a certain bullion was produced by the mint according to its corresponding standards of precious metal purity and content. In other words, a mint offering a .9999 pure gold bar in an assay card guarantees that all the gold bullion minted in that lot meets the purity standards inscribed on the card. This helps you feel confident that you buy precious metals knowing their true purity and authenticity.

What is an assayer?

A precious metal or gold assayer is a person who is a scientific professional in analyzing the ores or rock samples to identify their components and purity. However, an assayer also refers to a company which performs smelting or refining activities for obtaining pure precious metals.

Smelting vs Refining

Refining is a term that describes any process of separating and purifying the precious metal in order to increase its grade and purity. It includes both pyrometallurgical (dry) and hydrometallurgical (wet) processes. On the other hand, smelting is a form of extractive metallurgy which refers to the extraction of precious metal from ores by using heat. The precious metal is obtained by melting the samples with a chemical reducing agent to leave just the metal base behind.

Precious metal/gold grades

There are two different precious metal grades: the average precious metal grade (the price of the metals contained in the deposit) and the cut-off grade (an evaluation of the material below which mining becomes uneconomic). Since all mining operations usually come at a high cost, the financial analysis of a mining project strongly relies on the assay results of the ore and the precious metal grade – the larger the average grade, the more profitable is the mine.

Assaying Processes

The assay type depends on the precious metal’s type, as well as on the item which purity is being checked. The process starts with taking the sample, usually shavings obtained by drilling into the metal or grabbing a metal sample in its molten state (before striking the bullion). Then the assayers choose one of the most common types of assaying:

Destructive methods:

  • Fire Assay – one of the oldest and most accurate, yet totally destructive, methods for checking the precious metals purity content, particularly of gold and silver. Certain amounts of gold and silver are placed in a disposable crucible or cupel to check the amount of impure or non-precious metals in the sample. This method is standard for valuing gold ores, and it is also used by major refineries and mints to test their gold and silver bullion.

Fire assaying starts with fusing or dissolving the rock/metal sample in a clay or ceramic crucible by using a lead glass flux. This flux is a mixture of materials selected by a laboratory chemist, usually consisting of potassium carbonate, sodium carbonate, borax, flour and litharge (lead oxide). The rock/metal sample is mixed with the flux and heated to 1,100-1,200 °C (2,012-2,192 °F) to obtain a reaction. Once the reaction is completed, the crucible is removed to reveal the top layer of molten glass and the sinking bottom layer (“button”) of precious metal. This part of the process is called fusion. After pouring off the molten glass (it doesn’t contain any valuable metals), the remaining metal is poured into a mold and cooled down until solidification. The solid metal, usually containing lead, silver, and gold, is later removed from the mold. The next part of the fire assay is called cupellation. The mass of lead metal is placed on a special cupel made from bone ash since this material absorbs only the lead oxide and not the metal. Then the metal is blasted with hot air to oxidize the lead. The obtained lead oxide is volatilized off or absorbed into the cupel. The material (bead) that is left is weighted – it consists of all the silver and gold originally contained in the sample. Silver is separated from gold by using a solution of diluted nitric acid (sodium nitrate) which dissolves the silver and not the gold. The remaining pure gold is weighted. The silver’s weight is obtained by subtracting the gold’s weight from the bead’s weight.

  • Dry Assaying – a well-known method also used for silver and gold. Special chemical cleaning agents, called fluxes, are heated with the metals. As a result, a combination of impurities is created which later turns into a slag. This process separates the precious metals making its purest form settle at the bottom. The mixture is left to cool down, and after that, the slag gets chipped away. The remaining metal is then weighted and compared.
  • Wet Assaying – during this process, the sample is dissolved in solvents. The formed solution is chemically analyzed by the assayer through using electrolysis or salts to separate the precious metal.

Non- Destructive methods:

  • Spectrograph Assaying – this type of assaying requires the metal sample to actually emit light by passing an electrical discharge through the sample. The assayers analyze the light’s intensity and strength which allows them to identify the precious metal content of the sample.

  • X-Ray Fluorescence Assaying – just like in spectrograph assaying, this testing method requires the metal to actually emit X-rays by irradiation using an X-ray beam. The assayer identifies the precious metal based on the intensity level of the X-rays that it emits.

X-Ray Fluorescence Assayingis a modern non-destructive technique used to identify and determine the elements’ concentration in liquid, solid, and powered precious metal samples. The XRF assay takes about three minutes and has an accuracy of 2 to 5 parts per thousand. The process starts with melting the precious metal in a furnace and then stirring it to obtain a homogenous mix. After that, a metal sample is taken from the center of the molten mix, by using a vacuum pin tube. This sample is then tested with the X-Ray Fluorescence Spectroscopy to determine its purity.

Other Methods of Assaying – there are also different assaying processes for testing the purity of different metals: titration for silver assaying, cupellation as a gold assay, and ICP OES (Inductively Coupled Plasma Optical Emission Spectrometry) for valuing platinum.

Titration a technique through which a solution with known concentration (titrant) is used for determining the concentration of an unknown solution (analyte).

Cupellationsecond process partof the Fire Assay

ICP OESa major technique for elemental analysis of precious metal samples. If the sample is solid, it’s first dissolved and mixed with water prior to being fed into the plasma. The plasma’s atoms emit light (photons) with a characteristic wavelength for each element. One or more optical spectrometers record and calibrate this light against standards, providing a quantitative analysis of the original precious metal sample.

Why must Precious Metals be Assayed?

Purity is crucial for producing and selling precious metal bullion hence assaying is a fundamental process of their manufacturing. The key reason for performing a silver or gold assay is to ensure that the bullion stroke from these precious metals meets the mint’s requirements and standards. Whether you want a silver, gold, platinum, or palladium item, you would like to be sure that you own the required purity as the mint claims. Several governments and national mints, such as the South African Mint, the Royal Canadian Mint, the Austrian Mint, the Australian Perth Mint, as well as the US Mint, guarantee the precious metal content and purity of their bullion coins. This assurance is a form of assaying both the raw metal and finished coins. But some mints don’t just test the purity, but also the honesty, like the Royal Mint which still uses the “Trial of the Pyx” – an old ceremonial process for assaying newly minted coins and confirming their accordance with the required standards.

What is an Assay Card? Assay Types

Most bullion pieces are offered in a special proof of assay. Items with smaller ounces usually come sealed in assay cards that display the information about the assay and their date of creation. Larger bullion pieces are accompanied by an assay certificate which is similarly designed to serve as a proof of purity and authenticity. Both of them are issued to assure collectors and investors that their purchases are genuine and pure. The mint usually seals the small bullion piece into the card, which bears the same serial number, weight and purity, mint info and stamp, bar code and any appropriate details. Most gram assay cards have the same size as a credit card and can easily fit in a wallet, but they fit the best in a safe deposit box or bullion vault. Besides, solely the presence of a card or certificate isn’t enough. The information displayed on an assay is also important because it contains the individual serial number that acts as proof of the bullion’s integrity and authenticity. A reliable assay card will also include the details about the specific type of the precious metal and the mint mark, certifying it’s promised purity. All these details on the assay are instrumental because they assure the buyer that the item is a legit and pure product.

What is a Certificate of Authenticity

The Certificate of Authenticity (CoA or COA) represents a seal or a sticker placed on a certificate or a piece of paper. This Certificate of Authenticity seal guarantees that the bullion item or coin is authentic. However, unlike an assay, there is no detailed process that certifies the exact the purity of the item. Also, a COA doesn’t seal the bullion piece like an assay card. Though, a COA contains vital details such as the authenticity and approval stamp, purity, and mint mark, acting as a proof that the item is legit. Some bullion pieces aren’t accompanied by a COA for different reasons, like products sold in bulk, or they may come with an assay, instead.

Bullion Products offered with Assay

Bullion bars are usually sold with an assay proof because they have high purity, and are large and valuable. However, some special bar releases or limited edition coins may also come with an assay to certify their value and authenticity. Regular bullion coins usually don’t come with assays.

Bullion Products offered with COA

Often limited or special coin releases are sold with a COA which proves their authenticity. Usually these coins are commemorative pieces hence the proof of authenticity is a priority while the proof of purity is a bonus. For this reason, COA typically accompanies coins or exclusive pieces and not bars.