How Gold Purity Is Tested — Methods Explained for Sellers

When you sell gold, the price hinges on one number: purity. Before a buyer pays you, they verify how much pure gold your item actually contains. Understanding the testing methods helps you spot a fair process — and walk away from a shady one.

1. XRF Analysis — The Modern Standard

X-ray fluorescence (XRF) is the most accurate and trusted method. A machine fires harmless X-rays at the gold and reads the exact composition of every metal present, displayed on a screen in seconds.

• Non-destructive: Your item is never cut, scratched, or damaged
• Highly accurate: Reads purity to a fraction of a percent
• Transparent: You see the same result the buyer does

2. Touchstone Test — The Traditional Method

The oldest method still in use. The gold is rubbed on a dark stone to leave a streak, then test acids are applied. The colour reaction indicates the karat. It is quick and low-cost but relies heavily on the tester's skill and only assesses the surface.

3. Acid Test

A drop of nitric acid is applied to a small scratch on the metal. Pure gold does not react; lower-purity gold or fakes discolour. It is a reliable indicator of whether something is real gold, but it is a destructive test (leaves a tiny mark) and gives only an approximate karat.

4. Density / Specific Gravity Test

Gold is unusually dense. By weighing an item in air and then in water, its density is calculated and compared to pure gold's known value. It is useful as a cross-check but can be fooled by certain alloy combinations, so it is rarely used alone.

What This Means for You as a Seller

• Prefer a buyer who uses an XRF machine and shows you the reading
• Be cautious if testing happens out of your sight
• Surface-only methods can miss gold-plated or filled items — XRF does not
• Insist on seeing the weight and purity that your final price is based on

The Bottom Line

A trustworthy buyer tests openly and explains the result. XRF is the gold standard for both accuracy and transparency. If a buyer hides the testing process or rushes you past the purity reading, treat it as a warning sign and take your gold elsewhere.