No single screening method answers every question
Visual inspection and hallmarks are fast but can be misleading. Weight and dimensions are useful for recognized bullion, while density can identify obvious mismatches but may not detect every plated or composite counterfeit.
A credible workflow combines methods based on the item's form, expected alloy, value and whether the test must be non-destructive.
Surface tests have limits
Acid testing compares a rubbed sample with known reactions and is widely used for jewellery. It is inexpensive, but technique and sampling matter, and surface plating or solder can distort the result.
X-ray fluorescence can quickly estimate surface composition without damaging the item. It is powerful screening equipment, but it reads a limited depth and does not by itself prove that the interior matches the surface.
Testing should be recorded
For a transaction, the dealer should record the item, photos, weight, method, result, exceptions and who performed the test. High-value or unusual material may need escalation to a refiner, assayer or specialized authenticator.
A confirmed offer should record the verified weight, purity and calculation. An online estimate based on the karat you enter remains a starting point until the item is assessed.
Sources & further reading.
Meridian guides are educational. They are not legal, tax or investment advice, and they do not create an offer to buy or sell gold or silver.