How is bullion purity determined?

Bullion purity is expressed as fineness (parts per thousand, such as .999 or .9999) or, for gold, sometimes as karats, and it is established by the mint or refiner through assay and then stamped on the item. Buyers like Accurate Precious Metals confirm that stamp with their own testing before paying for it.

Reading the numbers

Fineness tells you how much of the piece is the named metal. A .999 silver bar is 99.9% silver; a .9999 gold bar is 99.99% gold, with the balance being trace elements. Karat works on a scale of 24: 24k is 99.9% or better, 22k is 91.7%, 18k is 75%, 14k is 58.3% and 10k is 41.7%. Most bars and rounds are .999 or finer. Some well known coins are deliberately alloyed for durability: the American Gold Eagle and South African Krugerrand are 22k (.9167), yet each still contains a full troy ounce of pure gold because the coin weighs more than an ounce. The American Gold Buffalo and Canadian Gold Maple Leaf are .9999 fine. Purity and weight together give the metal content, which is what pricing is based on.

How purity is established at the source

Government and private mints refine metal to a target fineness and verify it by assay before striking. The result is stamped directly on the bar or coin along with the weight and often a serial number, and many bars ship in sealed assay cards with a certificate. Government mint coins carry legal tender status and published specifications, which is one reason they command higher premiums than generic rounds. Those markings are a strong signal, but stamps can be faked, which is why any serious buyer tests again.

How a buyer verifies it

• Weight and dimensions. Genuine bullion matches its published specifications closely. A one ounce coin should weigh 31.1035 grams (a troy ounce, heavier than the 28.35 gram kitchen ounce) plus any alloy, and have the correct diameter and thickness.
• Magnet test. Gold, silver and platinum are not magnetic. Attraction to a magnet means a base metal is present.
• Electronic testers measure conductivity and other properties without marking the piece.
• XRF analysis reads the surface composition using x-ray fluorescence and reports each element as a percentage, quickly and without damage.
• Acid testing is used mainly on jewelry and scrap, where a small scratch is acceptable.
• Fire assay is the refinery standard for definitive purity and is part of the refining process itself.

At our Salem, Oregon facility you can watch this happen. Staff weigh and test your bullion in front of you, explain the result, and price it against the live market; spot gold is currently around $4,272.97 and spot silver around $63.64 per troy ounce. Because we are the refinery, verification is part of our daily work rather than an extra step. If you are buying, our bullion buyers guide explains how to read the markings on the products we sell. If you are selling, gold bullion and silver bullion are both priced at close to the live spot price.