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What is an Assay?

When collecting or selling bullion or coins, you may have noticed that some items come in an assay card, or are accompanied by a certificate of authenticity. In the bullion industry, the definition of assaying has two meanings. In precious metal refining, an assay process is a test procedure for measuring and analyzing the purity of a metal. This procedure includes determining its composition in ores, alloys, mineral deposits and precious metals. This way mints assure that the bullion meets its precious metal standards of content and purity.

Gold smelting, refining.

Methods of Assaying

Assaying processes depends on the precious metal type and the particular piece that is being analyzed. Each assay starts with taking a rock or molten metal sample and continues with one of the following methods:

Destructive methods:

  • Fire Assaying – the oldest, most accurate, and destructive assay method. The sample is placed in a crucible and heated to find out the amounts of non-precious and precious metals. It’s a standard method for testing precious metal bullion in mints and refineries.
  • Dry Assaying – heating fluxes, special chemical cleaning agents, together with the sample, to let the precious metals separate, cool down and settle at the bottom.
  • Wet Assaying – dissolving the sample by using solvents and chemically analyzing the solution.

Non-Destructive methods:

  • Spectrograph Assaying – analyzing the intensity and strength of the light emitted by the sample when passing an electrical discharge through it.
  • X-Ray Fluorescence Assaying – identifying the precious metal and its purity by irradiating the sample with an X-ray beam. Analyzing the level of intensity of the X-rays emitted by the sample.

Other Assaying Methodssilver assaying through titration, gold assay by cupellation. Inductively Coupled Plasma Optical Emission Spectrometry (ICP OES) for assaying platinum.

Assay Types

Bullion pieces mostly arrive in assays as a special proof. Small bullion pieces are often sealed in assay cards which bear their date of creation and assay info. Larger bullion pieces usually come with an assay certificate which has a similar design and acts as a proof of authenticity and purity. Both assay cards and assay certificates assure the sellers and buyers that the bullion product is pure and legit.Gold bars is assay.

What is a Certificate of Authenticity?

A COA (Certificate of Authenticity) is a sticker or a seal placed on a piece of paper or certificate. This Certificate of Authenticity seal is a warranty that the bullion coin or piece is authentic. Though, unlike an assay, a COA doesn’t guarantee a thorough process which certifies the exact purity of the piece. The COA also doesn’t seal the bullion like the assay card does.

However, the COA displays essential details, such as the approval and authenticity stamp, the mint mark, and purity, serving as a proof that the bullion item is genuine. Some precious metal pieces don’t come with COAs, like bullion offered in bulk, or they may come accompanied with an assay instead.

Certificate of Authenticity

Assay products vs. COA products

Bullion bars ordinarily arrive with an assay proof because they are large, valuable, and have high purity. Limited or special coin releases, on the other hand, with a certificate of authenticity which proves their genuineness. Sometimes, limited edition coins and special bar releases also come with an assay.  

Precious metal assaying is fundamental both for producing and selling bullion. Both assays and certificates of authenticity assure the buyer or owner that the precious metal item was minted according to the mint’s standards and requirements of precious metal purity and content.