What does .999 fine mean on a silver bar?

It means the bar contains 999 parts pure silver per 1,000 total parts, or 99.9 percent silver. This is the standard purity for investment-grade silver bullion and the minimum required for IRA eligibility.

Is 24K gold the same as .999 fine gold?

They are very close. 24K indicates gold of 99.9 percent purity or higher. In millesimal terms, 24K gold is .999 fine at minimum, though many modern products achieve .9999 fineness (four nines).

Why are American Gold Eagles only 22K but still IRA-eligible?

The IRS granted a specific exemption for American Gold Eagles due to their status as official US legal tender. Despite being alloyed to 22K (.9167 fineness), each Eagle contains a full troy ounce of pure gold; the coin simply weighs more than one troy ounce total.

Can I test gold purity at home?

Yes. A Sigma Metalytics Precious Metal Verifier, a precision scale for specific gravity testing, or a smartphone ping-test app can all help verify authenticity at home. For definitive results, a fire assay at a certified laboratory is the gold standard.

Is .9999 gold worth more than .999 gold?

The additional purity adds a negligible amount of gold content. Any premium difference between .9999 and .999 products is driven by the specific product's demand, mint reputation and collector appeal rather than the tiny difference in gold content.

What is sterling silver and is it a good investment?

Sterling silver is .925 fine (92.5 percent silver, 7.5 percent copper). While sterling silverware and jewelry can have collectible value, it is not considered investment-grade bullion, carries higher premiums per ounce of pure silver content, and is not eligible for IRA inclusion.

How do I verify the purity of a coin I bought online?

Buy from reputable dealers like MintBuilder who source directly from mints and refineries. Upon receipt you can verify with a Sigma tester, a precise scale for weight and dimensions, or an acoustic ping test. If in doubt, any local coin dealer with XRF equipment can test the piece non-destructively.

Understanding Gold and Silver Purity: Karat, Fineness and Millesimal Guide

Gold and silver purity is the single most important factor that determines a precious metal product's intrinsic value, IRA eligibility and market acceptance. Whether you are examining a 24K gold coin, a .999 fine silver bar or a piece of 18K jewelry, understanding how purity is measured, tested and certified will make you a more confident buyer. This guide explains the karat system, millesimal fineness, assay testing and hallmarks so you can evaluate any gold or silver product with authority.

What Is Precious Metal Purity?

Purity refers to the proportion of the target precious metal in a given item relative to other metals or alloys mixed in. Pure gold is soft and prone to scratching, which is why coins and jewelry often incorporate small amounts of copper, silver or zinc to improve durability. Silver products follow a similar logic, though investment-grade silver bars and coins are typically refined to very high purity levels.

Purity is expressed through several systems, each developed for different markets and historical traditions. The three you will encounter most often are the karat system, millesimal fineness and the older fineness-fraction notation.

The Karat System for Gold

The karat system divides gold purity into 24 parts. Pure gold is 24 karat (24K), meaning all 24 parts out of 24 are gold. Lower karat numbers indicate a proportionally smaller gold content:

24K – 99.9% or higher pure gold. This is the standard for investment-grade gold bars and many bullion coins such as the Canadian Gold Maple Leaf and the Australian Gold Kangaroo.
22K – 91.67% gold. The American Gold Eagle and the South African Krugerrand use 22K gold, with copper and silver making up the remaining alloy for added durability.
18K – 75% gold. Common in fine jewelry but generally not used for investment-grade bullion.
14K – 58.3% gold. Popular in everyday jewelry in the United States.
10K – 41.7% gold. The minimum karat designation that can legally be sold as gold in the US.

For investment purposes, 24K and 22K are the standard. The IRS requires gold held in a self-directed IRA to be at least .995 fine (essentially 24K), with a specific exception for the American Gold Eagle at 22K. See our guide to IRA-eligible gold products for a complete list.

Millesimal Fineness: The Universal Standard

Millesimal fineness expresses purity in parts per thousand. A gold bar stamped .999 contains 999 parts gold per 1,000 total parts. This system is used globally for both gold and silver and is the standard on investment-grade bullion products.

Common Gold Fineness Levels

.9999 (four nines fine) – The highest commercial purity, found on Canadian Gold Maple Leafs and many LBMA-approved gold bars.
.999 (three nines fine) – Standard for most investment-grade gold bars and coins.
.995 – The minimum fineness for LBMA Good Delivery gold bars and the IRS minimum for IRA-eligible gold.
.9167 – Equivalent to 22K. Used for American Gold Eagles and Krugerrands.

Common Silver Fineness Levels

.9999 (four nines fine) – Found on Canadian Silver Maple Leafs and select premium silver bars.
.999 (three nines fine) – The standard for investment-grade silver bars, rounds and most sovereign silver coins including the American Silver Eagle.
.925 (sterling silver) – A historical alloy of 92.5% silver and 7.5% copper, used in flatware, jewelry and some commemorative coins. Not IRA-eligible.
.900 (coin silver) – Used in pre-1965 US dimes, quarters and half dollars. Collected for their silver content but not IRA-eligible.

The IRS minimum fineness for silver held in an IRA is .999. Our IRA-eligible silver guide details exactly which products qualify.

Assay Testing: How Purity Is Verified

An assay is a laboratory analysis that determines the precise purity of a metal sample. Several methods are used in the precious metals industry:

Fire assay (cupellation) – The oldest and most accurate method. A small sample is melted with lead and heated in a furnace to separate base metals. The remaining precious metal bead is weighed to calculate purity. Fire assay is accurate to parts per ten thousand and is the benchmark for LBMA certification.
X-ray fluorescence (XRF) – A non-destructive method that uses X-rays to identify the elemental composition of a sample's surface. XRF analyzers are widely used by dealers and refiners for quick verification but measure only the outer layer, so they can be fooled by sophisticated counterfeits with gold-plated tungsten cores.
Sigma Metalytics Precious Metal Verifier – A portable device that measures electrical resistivity through the full thickness of a coin or bar. Different metals have distinct resistivity signatures, making it effective at detecting tungsten-filled counterfeits. Many reputable dealers use Sigma devices as a point-of-sale verification tool.
Specific gravity testing – Measures the density of a piece by comparing its weight in air to its weight submerged in water. Gold's exceptionally high density makes this a useful screening tool, though tungsten's similar density limits its effectiveness for gold specifically.
Ping test (acoustic analysis) – Striking a coin and analyzing the resulting sound frequency. Genuine gold and silver produce characteristic frequencies that differ from base metals and counterfeits. Free smartphone apps exist that automate this analysis.

Hallmarks and Mint Marks

Hallmarks are stamps or engravings on a precious metal item that certify its purity, origin and manufacturer. They serve as a quality guarantee and have been used for centuries. On investment-grade bullion you will typically find:

Fineness mark – The millesimal fineness such as .999 or .9999.
Weight – Expressed in troy ounces, grams or kilograms.
Manufacturer or refiner logo – Identifies the entity responsible for the product's purity claim.
Serial number – Found on many bars for tracking and authentication purposes.
Country of origin or mint mark – Sovereign coins carry the issuing government's official marks.

When buying from a reputable source like MintBuilder, every product's purity is guaranteed by the issuing mint or refinery. For additional peace of mind, review our guide on gold coins and gold bars to understand what markings to expect on the most popular products.

How Purity Affects Pricing and Premiums

Higher purity does not always mean a higher premium. The premium you pay above the current spot price depends on manufacturing costs, demand, collectibility and dealer margin—not purity alone. For example:

A 1 oz .9999 fine Canadian Gold Maple Leaf often carries a similar or slightly higher premium than a 1 oz .9167 fine American Gold Eagle, even though the Eagle contains slightly less pure gold. Both contain one full troy ounce of gold; the Eagle simply weighs a bit more to compensate for its alloy.
Generic .999 fine silver rounds typically carry lower premiums than sovereign coins of the same purity because they lack government backing and collector appeal.

The practical takeaway: focus on total gold or silver content (usually expressed in troy ounces) and the premium over spot rather than fixating on the last decimal of fineness. Our coins vs. bars comparison explores how format affects premiums in detail.

Purity and IRA Eligibility

The IRS sets minimum purity standards for precious metals held in a self-directed IRA:

Gold – Must be .995 fine or higher, with a specific exception for American Gold Eagles (.9167).
Silver – Must be .999 fine or higher.
Platinum – Must be .9995 fine or higher.
Palladium – Must be .9995 fine or higher.

Products that fall below these thresholds—such as sterling silver, pre-1965 US junk silver, or 18K gold jewelry—cannot be held in an IRA. Our guides to IRA-eligible gold and IRA-eligible silver provide complete product lists that meet these standards.

Frequently Asked Questions

What does .999 fine mean on a silver bar?: It means the bar contains 999 parts pure silver per 1,000 total parts, or 99.9 percent silver. This is the standard purity for investment-grade silver bullion and the minimum required for IRA eligibility.
Is 24K gold the same as .999 fine gold?: They are very close. 24K indicates gold of 99.9 percent purity or higher. In millesimal terms, 24K gold is .999 fine at minimum, though many modern products achieve .9999 fineness (four nines).
Why are American Gold Eagles only 22K but still IRA-eligible?: The IRS granted a specific exemption for American Gold Eagles due to their status as official US legal tender. Despite being alloyed to 22K (.9167 fineness), each Eagle contains a full troy ounce of pure gold; the coin simply weighs more than one troy ounce total.
Can I test gold purity at home?: Yes. A Sigma Metalytics Precious Metal Verifier, a precision scale for specific gravity testing, or a smartphone ping-test app can all help verify authenticity at home. For definitive results, a fire assay at a certified laboratory is the gold standard.
Is .9999 gold worth more than .999 gold?: The additional purity adds a negligible amount of gold content. Any premium difference between .9999 and .999 products is driven by the specific product's demand, mint reputation and collector appeal rather than the tiny difference in gold content.
What is sterling silver and is it a good investment?: Sterling silver is .925 fine (92.5 percent silver, 7.5 percent copper). While sterling silverware and jewelry can have collectible value, it is not considered investment-grade bullion, carries higher premiums per ounce of pure silver content, and is not eligible for IRA inclusion.
How do I verify the purity of a coin I bought online?: Buy from reputable dealers like MintBuilder who source directly from mints and refineries. Upon receipt you can verify with a Sigma tester, a precise scale for weight and dimensions, or an acoustic ping test. If in doubt, any local coin dealer with XRF equipment can test the piece non-destructively.

Make Informed Purchases With Confidence

Understanding purity empowers you to evaluate any precious metals product accurately, avoid overpaying for misleading claims and ensure your purchases meet IRA requirements when applicable. Browse MintBuilder's gold collection and silver collection to find investment-grade products with verified purity from the world's most trusted mints and refineries.