When shopping for gold, whether for jewellery or investment purposes, you'll encounter terms like "24 karat," "999.9 fineness," or "22K gold." Understanding these purity measurements is essential for making informed purchasing decisions and accurately valuing your gold holdings. This comprehensive guide explains everything Australian gold buyers need to know about gold purity.
What Is Gold Purity?
Pure gold, in its natural refined state, is a soft, bright yellow metal that's too malleable for many practical applications. To improve durability and alter properties like colour and hardness, gold is typically alloyed with other metals such as silver, copper, zinc, or palladium.
Gold purity measures how much of a gold item is actually gold versus other alloyed metals. This purity is expressed using two main systems: karats and fineness. Understanding both systems helps you compare products and calculate the actual gold content of any item.
The Karat System Explained
The karat system divides gold purity into 24 parts. Pure gold is 24 karats (24K), meaning all 24 parts are gold. Lower karat numbers indicate the presence of other metals in the alloy.
24 Karat Gold (99.9%+ Pure)
24K gold is essentially pure gold, containing 99.9% or higher gold content. This is the standard for investment-grade gold bars and many bullion coins. The Perth Mint's investment products, for instance, are refined to 99.99% purity (sometimes written as "four nines fine").
24K gold is ideal for investment because you're paying for actual gold content with minimal alloy. However, its softness makes it impractical for everyday jewellery that requires durability.
22 Karat Gold (91.7% Pure)
22K gold contains 22 parts gold and 2 parts other metals, resulting in 91.7% gold content. This purity level offers a balance between high gold content and improved durability compared to pure gold.
Many bullion coins, including the South African Krugerrand and the Australian Nugget (in its original form), use 22K gold. The small percentage of alloy metals adds durability while maintaining a high gold value. 22K is also popular for high-end jewellery in many cultures.
18 Karat Gold (75% Pure)
18K gold contains 75% gold and 25% other metals. This is a popular choice for fine jewellery, offering good durability while maintaining a significant gold content. The alloying metals can create different colours—white gold uses palladium or nickel, while rose gold uses copper.
From an investment perspective, 18K jewellery contains substantially less gold per gram than investment-grade bullion, and the craftsmanship premium means you pay above the intrinsic gold value.
14 and 10 Karat Gold
14K gold (58.3% pure) and 10K gold (41.7% pure) are common in more affordable jewellery. While durable and suitable for everyday wear, these lower purities contain significant amounts of base metals. In Australia, 9K gold (37.5% pure) is the legal minimum to be called "gold."
These lower karat golds are generally not considered suitable for investment purposes due to their lower gold content per unit weight.
The Fineness System
The fineness system expresses gold purity as parts per thousand. This system is preferred for investment products as it provides greater precision than the karat system.
Common Fineness Levels
999.9 (Four Nines Fine): 99.99% pure gold, the standard for most modern investment bars and coins. Perth Mint products meet this standard.
999 (Three Nines Fine): 99.9% pure gold, acceptable for many investment purposes and sometimes used in older gold products.
995: 99.5% pure, the minimum standard for London Good Delivery bars, the wholesale gold market's benchmark.
916.7: Equivalent to 22K gold, used in some bullion coins.
750: Equivalent to 18K gold, common in fine jewellery.
Why Purity Matters for Investors
When investing in gold, purity directly affects the value you receive. Consider two 1-ounce coins: one in 24K (999.9 fine) and one in 22K (916.7 fine). Despite both being "1 ounce," the 24K coin contains approximately 9% more actual gold.
Use our gold converter tool to calculate the value of gold at different weights, and always factor in purity when comparing products. A lower-purity product might appear cheaper per ounce, but the actual gold content could be less favourable.
Assaying and Certification
Reputable gold products come with assay certificates or hallmarks verifying their purity. The Perth Mint, for example, stamps its products with purity marks and provides certificates of authenticity for larger bars.
When buying gold, always verify the purity through official hallmarks, certificates, or reputable dealer guarantees. Avoid purchasing gold without clear purity verification, as counterfeit and misrepresented products exist in the market.
Calculating Gold Value Based on Purity
To determine the actual gold value of any item, multiply its weight by its purity percentage, then multiply by the current gold price per gram. For example:
An 18K gold chain weighing 20 grams contains: 20g × 0.75 = 15 grams of pure gold.
If the gold price is $138 per gram (check our live price for current rates), the gold content value is: 15g × $138 = $2,070.
This calculation helps you understand the intrinsic metal value, though retail prices for jewellery include significant premiums for design and craftsmanship.
Investment-Grade Gold Standards
For investment purposes, stick to products meeting recognised purity standards. The London Bullion Market Association (LBMA) certifies refineries producing Good Delivery bars, while individual mints like the Perth Mint maintain strict quality controls.
Investment-grade gold typically means:
- Minimum 995 fineness (99.5% pure), with 999.9 preferred
- Products from recognised mints or LBMA-certified refiners
- Clear hallmarks indicating weight and purity
- Accompanying assay certificates for larger bars
Gold Purity and Colour
Pure 24K gold always has that distinctive warm yellow colour. Variations like white gold, rose gold, or green gold result from alloying with different metals. While attractive for jewellery, these coloured golds are not suitable for investment as their value depends on factors beyond pure gold content.
Investment-grade gold should always appear in natural yellow gold colour, indicating minimal alloying with colour-changing metals.
Testing Gold Purity
Professional methods for verifying gold purity include X-ray fluorescence (XRF) analysis, specific gravity testing, and fire assay. For consumers, simple tests like the acid test or magnet test can help identify obvious fakes, though they're not definitive for determining exact purity.
If you're unsure about a gold item's purity, have it professionally assessed before buying or selling. Many jewellers and gold dealers offer testing services.
Conclusion
Understanding gold purity empowers you to make informed decisions whether buying jewellery or building an investment portfolio. For investment purposes, prioritise 999.9 fineness products from reputable sources like the Perth Mint. For jewellery, choose the karat level that balances your preferences for durability, colour, and gold content.
Always verify purity through official hallmarks and certificates, calculate the actual gold content when comparing prices, and use our gold price tools to stay informed about current market values. With this knowledge, you can confidently navigate the gold market and ensure you're getting fair value for your purchases.