Today, let’s talk about gold purity and composition.
Gold is a very soft metal, with a hardness of just 2.5 on the Mohs scale. Pure gold (99.99%) is softer than tooth enamel, making it relatively easy to scratch.
Interesting Fact:
In ancient times, merchants would bite gold coins to distinguish genuine gold from counterfeits.
A genuine gold coin would develop a small indentation when bitten and would not have the distinctive metallic taste of other metals, such as copper, commonly found in counterfeit coins.
Jewelry made from pure gold is not suitable for everyday wear because it is soft, easily bent, scratched, and damaged. To increase its strength and durability, other metals are added to gold to create an alloy.
The percentage of additional metals in the alloy determines its gold purity.
Gold purity indicates how much pure gold is contained in an alloy.
The highest purity grade, 999, represents investment-grade gold with virtually no impurities (99.9% gold).
There are two main systems for measuring gold purity: the karat system and the metric fineness system.
The Karat System
One of the oldest and most widely used systems in the world is the karat system.
* In gemstones, the term “carat” (ct) refers to weight rather than purity.
Interesting Fact:
In ancient times, people used plant seeds as units of weight. In the Roman Empire, the seeds of the evergreen carob tree (Ceratonia siliqua), commonly found in the Mediterranean region, became a reference for weighing valuable materials.
These seeds were traditionally associated with a weight of approximately 0.2 grams each. The unit of measurement was known as the “siliqua” (from the Latin word for a pod) and later became associated with the term “carat,” derived from Ceratonia.
How Did the Carob-Based Carat Become a Measure of Gold Purity?
In 309 AD, Emperor Constantine I began minting coins made from exceptionally pure gold, each weighing exactly 24 siliquae (or 24 carats). Due to their consistently high gold content, these coins were considered particularly prestigious. This tradition eventually contributed to the development of the karat system for measuring gold purity.
While a carat refers to weight when measuring gemstones, a karat in gold indicates the proportion of pure gold in an alloy. In other words, it shows how many parts of pure gold are contained in 24 parts of the total alloy.
The karat system commonly includes five gold purity grades: 9K, 10K, 14K, 18K, and 24K.
The highest grade, 24K, represents approximately 99.9% pure gold.
For example, 14K gold contains 14 parts pure gold and 10 parts other metals.
Dividing 14 by 24 gives us 0.58333, or approximately 583 parts of gold per thousand.
Gold purity grades correspond to the following values:
- 24K or 999 fineness — 99% gold
- 18K or 750 fineness — 75% gold
- 14K or 583 fineness — 58.3% gold
- 10K or 417 fineness — 41.7% gold
- 9K gold — the lowest of these grades, containing 37.5% gold
The Metric Fineness System
In post-Soviet countries, the metric fineness system was adopted in 1927. This system uses familiar purity grades such as 999, 750, 583, 500, and 375.
One notable exception occurred in 1994, when the 583 fineness standard was changed to 585 for practical reasons. This means the alloy contains 58.5% pure gold.
Incidentally, 585 gold is considered one of the most practical choices for everyday jewelry!
On the other hand, the higher the gold content in an alloy, the more resistant it generally is to oxidation and tarnishing.
Interesting Fact:
Gold alloys of 750 and 585 fineness produced in our region are sometimes considered less durable than their European 18K and 14K counterparts.
This difference is often attributed to alloy composition: locally produced gold may contain more soft copper, while European alloys may contain a higher proportion of silver.
Now you understand why gold jewelry in our region often has a reddish tint, while European gold tends to have a more yellow appearance!