The karat system is a standardized method used to express the purity of gold. In this system, gold purity is defined by how many parts, by weight, out of 24 are pure gold. For instance, 24-karat (24K) gold is considered pure gold, while lower karat values indicate that the gold is mixed with other metals to enhance durability or alter its color.

How the Karat System Works

Gold purity can be calculated with the formula:

Examples of Karat Conversions

• 24K Gold:

  24 24 X 100 = 100%

  Pure gold, containing no other metals.

• 18K Gold:

  18 24 X 100 = 75%

  Contains 75% gold and 25% other metals (such as silver, copper, or nickel).

• 14K Gold:

  14 24 X 100 = 58.3%

  Contains approximately 58.3% gold.

• 10K Gold:

  10 24 X 100 = 41.7%

  Contains about 41.7% gold.

The non-gold portion in these alloys is made up of various metals, which not only increase hardness but also reduce cost.

Understanding .925 in Jewelry

The term .925 is commonly seen in jewelry and refers to sterling silver. Pure silver, being 99.9% silver, is too soft for practical jewelry use, so it’s typically alloyed—usually with copper—to form a more durable material.

• Sterling Silver:
  Contains 92.5% silver, with the remaining 7.5% composed of other metals (often copper).
  The notation ".925" means 92.5% purity, which can also be written as 925 when expressed per 1000

  (i.e., 925 1000 = 0.925).

Regional Differences in Gold and Silver Standards

Gold Purity

• North America (USA and Canada):
  The karat system is standard. Gold jewelry is usually stamped with values like 14K or 18K to indicate its purity.

• Europe:
  Many European countries use the millésimal fineness system, which expresses gold purity as parts per 1,000. For example:

• 18K Gold:

  18 24 X 1000 = 750

  (Expressed as 750, meaning 750 parts per 1,000 are pure gold.)

• 14K Gold:

  14 24 X 1000 = 583

  (Expressed as 583.)

Some European countries may also use the karat system, but official hallmarks often display millésimal values.

Silver Purity

Both North America and Europe typically adhere to the .925 standard for sterling silver. In European markets, this might also be represented simply as "925" (without the decimal point). In some regions, higher purity silver is also popular, such as 950 (95% pure) or 999 (99.9% pure).

Summary of Key Points

• Karat System (North America):
  Gold purity is expressed in karats (e.g., 14K, 18K), where 24K equals 100% pure gold.

• Millésimal Fineness (Europe):
  Gold is often marked by its purity in parts per 1,000 (e.g., 750 for 18K gold, 583 for 14K gold).

• Sterling Silver:
  Defined as .925 or 925, meaning 92.5% pure silver mixed with other metals, typically copper.

The choice between using karats and millésimal fineness is primarily a matter of regional preference, yet the actual gold content remains identical regardless of the system used.

Understanding these systems is essential for both jewelers and consumers. Whether you are evaluating an 18K gold ring or purchasing sterling silver jewelry, knowing how purity is measured can help you make more informed decisions about quality, durability, and value.