Introduction: Why Purity Matters in Silver Bullion
When you start exploring the world of silver bullion, you'll quickly encounter a range of purity designations: .999, .9999, sterling, coin silver, and more. Understanding what these terms mean is fundamental to making informed buying decisions and accurately assessing the value of any silver you own or are considering purchasing.
In this guide, we'll explain exactly how silver purity is measured, what the different grades mean in practice, and which purity you should look for when buying investment-grade silver bullion.
How Silver Purity is Measured
Silver purity is expressed as a decimal or parts per thousand, known as the millesimal fineness system. This system expresses the purity of a precious metal as parts per 1,000. So:
- .999 fine silver = 999 parts silver per 1,000 = 99.9% pure silver
- .9999 fine silver = 999.9 parts silver per 1,000 = 99.99% pure silver
- .925 sterling silver = 925 parts silver per 1,000 = 92.5% pure silver
- .900 coin silver = 900 parts silver per 1,000 = 90% pure silver
The higher the fineness number, the purer the silver. For investment purposes, .999 is the minimum standard you should accept for bullion coins and bars.
The Main Silver Purity Grades Explained
.999 Fine Silver (Three Nines Fine)
.999 fine silver is the standard purity for the vast majority of silver bullion coins and bars worldwide. It contains 99.9% silver, with the remaining 0.1% typically being trace amounts of other metals that are virtually impossible to eliminate entirely in the refining process.
Most of the world's most popular silver bullion coins are struck in .999 fine silver, including the American Silver Eagle and the 2013 American Silver Eagle. This purity level is universally recognised and accepted by bullion dealers worldwide.
.9999 Fine Silver (Four Nines Fine)
.9999 fine silver represents an even higher level of purity at 99.99% silver. The Silver Britannia has been struck in .9999 fine silver since 2013, making it one of the purest mainstream silver bullion coins available. Our 2025 Silver Britannia maintains this four-nines standard. The Chinese Silver Panda is also struck in .999 fine silver.
.925 Sterling Silver
Sterling silver is the standard used for most silver jewellery, cutlery, and decorative items in the UK. It contains 92.5% silver alloyed with 7.5% copper. Sterling silver is not considered investment-grade bullion. If you're buying silver as an investment, avoid sterling silver items unless you're specifically interested in their antique or decorative value.
.900 Coin Silver
Coin silver refers to the 90% silver alloy used in many historic circulating coins, particularly American coins minted before 1965 such as Morgan and Peace dollars. These are sometimes called junk silver in the US market. Coin silver items can be a cost-effective way to acquire silver, but they're less straightforward to sell than standard .999 bullion.
.958 Britannia Silver
Britannia silver is a high-purity standard (95.8% silver) used for some British silverware and hallmarked items. It was introduced in 1697 as a higher standard than sterling. This is distinct from the Silver Britannia bullion coin, which is struck in .9999 fine silver.
How to Identify Silver Purity
Hallmarks
In the UK, silver items are required by law to be hallmarked if they exceed certain weight thresholds. A UK hallmark includes the maker's mark, the assay office mark (London, Birmingham, Edinburgh, or Sheffield), and the fineness mark showing the purity: 925 for sterling, 999 for fine silver, and so on.
Mint Markings on Bullion Coins
Reputable bullion coins from government mints clearly state their silver content. The Silver Britannia is marked 999.9 FINE SILVER 1 OZ on the reverse. The American Silver Eagle is marked 1 OZ. FINE SILVER. These markings, combined with the mint's reputation, provide assurance of purity.
Assay Cards for Bars
Silver bars from reputable refiners come with assay cards or certificates that confirm their weight and purity. Always keep these with your bars as they make the bars easier to sell and provide important provenance documentation.
Does Higher Purity Mean Better Value?
Not necessarily. The difference in silver content between a .999 and a .9999 coin is just 0.1 grams per troy ounce, worth only a few pence at current silver prices. For pure investment purposes, the purity difference between .999 and .9999 is essentially irrelevant. What matters far more for UK investors are factors like CGT status, premium over spot, and liquidity.
As UK legal tender, Silver Britannias and other UK coins are exempt from Capital Gains Tax. Read our CGT guide for full details. And don't forget to plan your storage strategy before you buy - our storage guide covers all your options.
Silver Purity and Tarnishing
One practical consideration with high-purity silver is that it tarnishes more readily than lower-purity alloys. Sterling silver's copper content actually makes it slightly more resistant to tarnishing than pure silver. This is why proper storage is particularly important for .999 and .9999 silver bullion. Store your silver in airtight capsules or tubes, use silica gel to control humidity, and handle coins by the edges only to minimise fingerprint tarnishing.
Tarnishing does not affect the silver content or intrinsic value of bullion, but it can affect the appearance and potentially the numismatic value of collectible coins.
Which Purity Should You Buy?
For most UK investors, the answer is straightforward. For silver coins, buy .999 or .9999 fine silver coins from reputable government mints. The Silver Britannia (.9999) is our top recommendation for UK investors due to its CGT-free status. The Best Value CGT-Free Silver Coin offers excellent value at competitive premiums. For silver bars, buy .999 fine silver bars from recognised refiners, which offer the lowest premiums over spot for larger silver purchases. Avoid sterling silver, coin silver, and unbranded silver items for investment purposes.
A Note on Fake Silver
Unfortunately, counterfeit silver bullion exists. The most common fakes involve silver-plated base metal coins or bars. Buying from reputable, established dealers like 888 Bullion eliminates this risk entirely as we authenticate every item we sell. If you're buying from private sellers or unfamiliar sources, be aware of the risk and consider having items tested by a professional.
Final Thoughts
Understanding silver purity is one of the building blocks of confident bullion investing. Once you know what .999 and .9999 mean, how to read hallmarks, and why purity alone doesn't determine value, you're well equipped to make smart purchasing decisions.
Browse our full range of silver coins and bullion at 888 Bullion, and read our comparison of Silver Eagles vs Britannia Coins to help choose the right silver coin for your portfolio. If you're also considering gold, our guide on Gold vs Silver is essential reading. Our Hatton Garden team is always available to answer any questions about silver purity, authenticity, or investment strategy.