Lumo, an affiliated directory of local cash-for-gold buyers at lumo.gold, exists to help people find places to sell gold. Before comparing buyers, though, it helps to understand what you actually have. The single biggest factor in a gold item’s metal value, after its weight, is its purity. This guide explains how purity is measured, how to read the stamps on jewelry and coins, and why two rings that look alike can be worth very different amounts.
Why Gold Is Almost Never Pure
Pure gold is beautiful but soft. It scratches, bends and wears down easily, which makes it impractical for rings, chains and other jewelry worn every day. To make gold more durable and to change its color, jewelers mix it with other metals such as silver, copper, zinc, nickel or palladium. The resulting mixture is called an alloy.
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The proportion of gold in that alloy is its purity. The more gold, the richer the color and the higher the metal value per gram. The less gold, the harder and more durable the piece, and the lower its value as metal.
The Karat System
In the United States and many other countries, gold purity is expressed in karats, abbreviated K or kt. (This is different from the carat used to weigh gemstones, though the words share an origin.) The karat system divides gold into 24 parts. Pure gold is 24 karats. Each karat represents one twenty-fourth of the total.
Common karat values and their approximate gold content:
- 24K: about 99.9 percent gold, often described as fine gold.
- 22K: about 91.7 percent gold, common in jewelry in parts of South Asia and the Middle East and in some bullion coins.
- 18K: 75 percent gold, popular for fine jewelry.
- 14K: about 58.3 percent gold, the most common choice for jewelry in the United States.
- 10K: about 41.7 percent gold, the lowest karat generally sold as “gold” jewelry in the U.S.
- 9K: 37.5 percent gold, common in the United Kingdom and some other markets.
To calculate the gold fraction yourself, divide the karat number by 24. A 14K ring is 14 divided by 24, or roughly 58 percent gold.
Fineness Numbers
Many items, especially those made in Europe or for international markets, are stamped with a three-digit fineness number instead of, or in addition to, a karat mark. Fineness expresses purity in parts per thousand.
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- 999 or 999.9: fine gold (24K).
- 916 or 917: 22K.
- 750: 18K.
- 585: 14K. The figure is slightly higher than the exact 583 to ensure the alloy meets the 14K standard.
- 417: 10K.
- 375: 9K.
If you find a small “750” stamped inside a ring, that is a claim that the piece is 18 karat gold.
Hallmarks and Maker’s Marks
A purity stamp is only a claim. How much it can be trusted depends partly on where the piece was made.
In some countries, including the United Kingdom, precious metal articles above a certain weight must be tested by an independent assay office and stamped with official hallmarks before they can be sold as gold. These marks typically include a sponsor’s or maker’s mark, a fineness mark and the assay office’s symbol, sometimes with a date letter.
In the United States, there is no government assay requirement for jewelry. Federal law and Federal Trade Commission guidelines govern how gold may be marked and described. Under federal law, a manufacturer that stamps a quality mark is generally expected to stamp a registered trademark or maker’s mark alongside it, which helps establish accountability. Still, marks can be wrong, worn or deliberately misleading.
You may also see older marks such as “KP,” which stands for “karat plumb” and indicated that an item met its stated karat without falling below it.
What Gold Color Tells You, and What It Does Not
Gold comes in several colors depending on what it is alloyed with:
- Yellow gold is mixed mostly with silver and copper.
- White gold is alloyed with white metals such as palladium or nickel and is often plated with rhodium for extra brightness.
- Rose gold gets its pink tone from a higher proportion of copper.
Color does not indicate purity on its own. An 18K white gold ring and an 18K yellow gold ring contain the same proportion of gold. Very deep yellow can suggest higher karat, but lighting, wear and plating can make appearances misleading.
Purity and Value
The metal value of a gold item, often called melt value, depends on three things: its weight, its purity and the current market price of gold. In simple terms:
- Weigh the item, ideally in grams or troy ounces. One troy ounce is about 31.1 grams.
- Multiply the weight by the gold fraction (for example, 0.583 for 14K).
- Multiply the result by the current price of pure gold per unit of weight.
That calculation gives a rough idea of how much pure gold the item contains and what that gold is worth at the moment. What a buyer actually offers will be lower, because buyers must cover refining, testing and business costs. Lumo’s other guides explain spot prices and buyer spreads in more detail.
Purity matters a great deal. Two chains of the same weight, one 10K and one 18K, contain very different amounts of gold, so their metal values differ substantially.
Testing Purity
Reputable buyers usually verify purity rather than relying on stamps alone. Common methods include acid testing on a touchstone, electronic testers and X-ray fluorescence analyzers that measure metal composition without damaging the item. Asking how a buyer tests, and whether testing happens in front of you, is reasonable.
A Quick Summary
- Karats measure gold in twenty-fourths; fineness measures it in thousandths.
- Stamps are claims, not guarantees.
- Color does not reveal purity.
- Value depends on weight, purity and the market price.
This guide is general educational information. For a specific item, a qualified jeweler or appraiser can provide an expert assessment.
Quick check: What karat does the fineness stamp “750” indicate?
- 14K
- 18K
- 22K
Show answer
B. 750 means 750 parts per thousand, or 75 percent gold, which equals 18 karats.