How precious metals purity is tested and verified.

Testing purity is the plain work of confirming that a coin or a bar holds the metal and the fineness it claims to hold. No single test answers every question. A serious dealer works with a set of checks and reads them together. The weight and the dimensions of the piece come first, measured against the known spec of the coin or bar in question. A gold eagle weighs what a gold eagle weighs, and a fake that strays from that weight reveals itself at the scale. The magnet comes next. Gold, silver, platinum, and palladium are all non-magnetic. If a strong magnet pulls on a coin, the coin isn't what it claims to be. This first screen takes no special tools and rules out the crudest fakes.

Beyond those first two, the dealer will reach for the electronic conductivity meter, the ultrasound reader that looks for a tungsten core beneath the surface, a touchstone and an acid kit for the borderline call, and the XRF gun. XRF reads the X-ray signal that comes back from the metal and names the elements in the piece without cutting it open. It's the tool most trusted by dealers who handle many coins a day. And behind all of these stands the fire assay, in which a sample is melted and parted by chemical means to read the pure metal down to the last point. Fire assay is the truest test there is. It's also slow and destructive, which is why it stays in the refinery and not on the dealer’s desk.

A well-known coin carries its own proof. The rest is watchfulness.

The household reader of the market doesn't need a tungsten meter or an XRF gun to hold metal safely. The working answer is simpler. Buy the pieces the world already knows. A sovereign coin — an American Eagle, a Canadian Maple Leaf, a Krugerrand — carries its own proof in its weight, its dimensions, and its name. A bar from an LBMA-approved refiner moves on the trust already stamped into it. A serious dealer who reads these pieces every week can name a fake in seconds. The household buyer doesn't need to out-test the trade. The household buyer needs to buy from a source that already does the testing, and to ask for proof of it in writing.

A few plain checks keep the household holding honest. Ask the dealer what the piece weighs and read it on a jewelry scale. Ask how the piece measures and read it with a caliper. Keep the purchase paper that names the coin, the weight, the fineness, and the price the day it was bought. None of this replaces the dealer’s work. It backs it up with a paper record the household can read for itself. The plain rule of the house is that the trust in the coin and the trust in the dealer should both be set down in writing, not carried on good feeling alone.