Fineness vs. Karat Systems
Two systems measure gold purity: fineness and karats. Fineness expresses purity as parts per thousand. A .9999 fine gold bar contains 999.9 parts gold per 1000, or 99.99% pure gold. This is the standard for investment-grade bars from major refiners.
The karat system measures purity as parts per 24. Pure gold is 24 karat (24K). An 18K gold item contains 18 parts gold and 6 parts other metals, or 75% gold. The karat system is more common for jewelry, while fineness is standard for investment bullion.
You may also see purity expressed as a three-digit number. For example, 999 means 99.9% pure, while 9999 means 99.99% pure. Some bars display both systems: .9999 fine and 24K refer to the same purity level.
Investment-Grade Purity Standards
Most 1 oz gold bars from LBMA-accredited refiners are .9999 fine (99.99% pure). This standard, established by the London Bullion Market Association, ensures global acceptance and consistent quality. The LBMA Good Delivery rules specify minimum purity of 99.5% for large bars, but retail products typically exceed this significantly.
Some older bars or products from certain mints may be .999 fine (99.9% pure). While still investment grade, the 0.09% difference means slightly less gold content per bar. At current prices, this difference is minor but worth noting when comparing products.
Government mints sometimes use different standards. The American Gold Eagle, for example, is 22K gold (91.67% pure) with copper and silver added for durability. The coin contains exactly 1 oz of pure gold but weighs more than 1 oz total. This differs from bars, which are pure gold throughout.
How Purity Is Verified
Refiners verify purity through assay testing during production. Fire assay, the most accurate method, involves melting a sample and separating gold from other metals. X-ray fluorescence (XRF) provides non-destructive testing that can verify purity without damaging the bar.
Accredited refiners document purity through assay certificates that accompany their bars. These certificates state the exact fineness and are matched to bars by serial number. When you purchase a bar with an assay card, you receive third-party documentation of its purity.
For bars without documentation, dealers can perform XRF testing to verify purity before purchase or sale. This testing is standard practice for secondary market bars and provides confidence for both parties.
Why Purity Matters
Purity directly affects value. A 1 oz bar at .9999 fine contains marginally more gold than a 1 oz bar at .999 fine. More importantly, high-purity bars from recognized refiners command better resale prices due to their established quality and documentation.
Purity also affects appearance and handling. Pure gold is soft and can scratch easily. This is why investment bars typically come in protective packaging and why collectors avoid handling bars directly. The softness is actually a useful authentication indicator, as tungsten fakes would be noticeably harder.
For practical investment purposes, choosing .9999 fine bars from LBMA-accredited refiners ensures you receive maximum gold content with documentation that supports future resale. Learn more about refiner accreditation and its importance for investors.