What Is 18-Karat Gold? A Complete Guide to Gold in Jewelry
When you're looking for gold jewelry, it's very likely you've seen terms like 18k gold, 9k gold, 24k gold, or 750 thousandths. What does all of this mean? Is higher karat gold better? Is there really such a thing as pure gold jewelry? In this guide, we'll explain it all in a simple way.
What is a karat?
A karat is the unit of measurement that indicates the amount of pure gold contained in a piece of jewelry. It is calculated out of 24 parts — that is, a 24-karat piece of jewelry would be 100% pure gold, an 18-karat piece contains 18 parts of pure gold out of 24, and a 9-karat piece contains 9 parts of pure gold out of 24.
It is also expressed in thousandths — which is why you'll find the hallmark 750 (18k gold) or 375 (9k gold) engraved on jewelry. That number indicates how many parts out of every 1,000 are pure gold.
What is 18-karat gold?
18-karat gold — also called 18k gold or 750 gold — contains 75% pure gold and 25% other metals, usually copper and silver in varying proportions. It is the most widely used jewelry standard in Spain and in countries with a Mediterranean jewelry tradition.
That 25% of other metals is not a defect — it's a necessity. Pure gold is too soft to make jewelry that can withstand daily wear. By combining it with copper and silver, a much more resistant alloy is achieved that retains all the brilliance and value of gold. Furthermore, by varying the proportions of these metals, different gold colors are obtained:
- Yellow gold — the classic alloy with copper and silver
- White gold — palladium is added to achieve the silvery tone
- Rose gold — a higher proportion of copper, which gives that fashionable warm tone
In all three cases, the percentage of pure gold is exactly the same — 75%. What changes is the composition of the remaining 25%.
What about 9-karat gold?
9-karat gold — also called 375 gold — contains 37.5% pure gold and 62.5% other metals. It is the lowest legally recognized karatage in Spain as fine gold, and it is especially popular in the United Kingdom and northern Europe.
It has a very clear advantage: the price. Containing less pure gold, a 9k piece of jewelry can cost approximately half that of the same piece in 18k. This makes it a very attractive option for those who want authentic gold jewelry without a high outlay.
And here's an important point that many people don't know: 9k gold doesn't lose its color over time. It is authentic solid gold — it's not plated, it's not gold-filled, it doesn't have any coating on top. The color is part of the metal and doesn't wear off or chip. This radically differentiates it from gold plating or gold-filled, where a very thin gold layer covers a base metal that eventually shows through with use.
At Pepe Lozano Joyeros, we work with both 18-karat gold and 9-karat gold, always with their corresponding authenticity hallmark and quality certificate. You can see our selection of 9k jewelry in our 9K Selection collection.
Plated, gold-filled, and solid gold — not the same
We'd like to clarify a very common confusion. When you search for gold-colored jewelry online, you find three very different types of products:
- Solid 18k or 9k gold — authentic fine gold throughout the entire mass of the jewelry. The color never fades because it is the metal itself.
- Gold-plated — a very thin layer of gold over a base metal, usually steel or brass. With use, this layer wears off and the base metal begins to show. It can last months or a few years depending on the thickness of the plating.
- Gold-filled — similar to plated but with a slightly thicker layer of gold. It lasts longer than plated, but it is still a surface layer that also wears off over time.
The difference in durability and value is enormous. A 9k solid gold piece of jewelry is for life — a plated one is not.
Are there 24-karat gold jewels?
There's a widespread belief here that needs clarifying. Many people think that the highest quality jewelry is 24-karat — 100% pure gold. The reality is that in Spain it's practically impossible to find 24k gold jewelry, and there's a very specific reason for it.
24-karat gold is too soft to make jewelry. It scratches easily, deforms with knocks, and cannot withstand daily use. That's why in Spain — and in most countries with a jewelry tradition — 24k gold is reserved exclusively for investment ingots and coins. If someone offers you a 24k gold piece of jewelry in Spain, be suspicious — either it's an incorrect claim, or it's a piece so soft that it won't be suitable for wearing.
The highest quality standard in Spanish jewelry is 18-karat gold — with that 75% pure gold that guarantees both the richness of the metal and the necessary resistance for a piece of jewelry that lasts a lifetime.
How do I know what karatage my jewelry has?
Look for the hallmark engraved on the piece — it is mandatory by law in Spain. You will find the number 750 for 18k gold or 375 for 9k gold, engraved on the inside of the ring, on the clasp, or in a discreet spot on the jewelry.
At Pepe Lozano Joyeros, all our gold jewelry bears its authenticity hallmark and is sent with a quality certificate, free and insured shipping throughout Spain, and 15 days for exchange or return.