What Is Plumb Gold (History & Usage)

Whether you are a jewelry seller, collecting estate jewelry, or simply on the lookout to buy some gold, the term plumb gold can catch your attention. Most people want to get the purest piece for the money they invest. When purchasing any gold piece of jewelry, karat marks play an essential role.

Even though stamps weren’t mandatory in the past, they are a legal obligation nowadays. Similarly, marks with the karat number show the specific gold form, but some combinations don’t fit into the established framework. That is where this term kicks in. Let’s see what is plumb gold.


In the past, most people bought jewelry from jewelers with a good reputation. Not many people got a counterfeit piece until they started purchasing it from anyone. At one point, it was crucial to stop the frauds, and putting karat marks on gold pieces became part of the law in the US.

One of the most common problems was gold jewelry with a stamp that showed a higher gold percentage than it truly is. For example, a 13.5 karat gold often had a 14K stamp.

There was no law about that half-karate gold until 1981, so manufacturers could stamp the 14K mark on pieces that weren’t indeed the real thing. Without any requirement about it, such a practice wasn’t illegal.

What is Plumb Gold?

What is Plumb Gold

In 1981, the US Government passed the National Gold and Silver Marking act. That act no longer allowed the round-off or half-karate gold. Therefore, gold had to be at least 14K to be legally stamped that way, and its technical term was – plumb gold.

The word plumb means true. It comes from the French term plum, meaning completely or exact. Hence, the name itself shows that the gold karats stated on the jewelry are correct.

It means that, for example, a 17.9 karat gold needs to be stamped 17K, unlike the past practice when it would probably be stamped as 18K gold.

Nowadays, you can sometimes see a marking KP on a piece of jewelry, meaning Karat Plumb. For example, 18KP implies that the gold is at least eighteen karats plumb gold, meaning the mark gives assurance that value can’t be less.

Always choose the appropriate karat according to your preferences, but be aware of particular types’ limitations. Higher karat gold is more resistant to tarnishing and will appear more yellow because it is purer.

On the other hand, gold blended with more alloys is stronger. Accordingly, the fewer karats in a necklace or a ring, the stronger it will be.

Meaning of Karat Stamps

Meaning of Karat Stamps
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As you have already known, only 24K gold is pure gold. If a jewelry piece is 14K, only 14 out of 24 parts are pure gold. The other ten parts are a mixture of metal combined with one or more other elements.

For instance, you will get white gold by adding silver as an alloy, while extra copper colors gold in a reddish shade, so you get rose gold. Most other alloys won’t affect gold color much, and you can see jewelry in different goldish variations.

In the US, the minimal standard for gold is 10K, or 47.5% pure gold. However, many other countries allow 9K, or 37.5% pure gold jewelry, to market it as gold.

The most frequently used karat values in the US are 10K, 14K, 18K, 20K, and 22K. Since 24K gold is too soft, it is rare to see it in jewelry. Keep in mind that the exact value of the karat can slightly vary from what is stamped on an item unless jewelry is marked as Karat Plumb.

When you want to calculate the purity percentage of your piece of jewelry, divide the karat number by 24, then multiply it by 100.

Discover the Difference

Plumb gold vs. gold-plated

Many people confuse plumb gold with plated gold because of its mark KP. Be aware that manufacturers mark gold-plated jewelry with a HEG mark. That stands for heavy electroplated gold, so it can help you spot the difference.

Gold plating is the process of coating the base metal with a thin gold layer. The standard encloses a wide range of its thickness, so you can’t know exactly how much gold is plated in the layer. That is never the case with plumb gold since you have always know what to expect in this particular case.

Gold-filled vs. gold-plated

Even though the term ‘gold-filled jewelry’ indicates that jewelry is filled with gold, the thick layer of durable, solid gold is actually on the outside surface. The process involves pressure bonding of many solid gold layers over the core of high-quality brass with maximum heat.

The main difference between gold-filled and gold-plated jewelry is in the connections between the gold layer and the base metal. It is thicker and attached in gold-filled type so that it is more durable. For instance, a pocket watch with 25 years warranty is gold-filled for sure. It won’t wear out quickly, thanks to a thick gold layer.

RGP is another mark to differentiate, meaning rolled-gold plate. It represents that the metal is physically gold-filled, but the gold layer is too thin for authentic gold-filled jewelry.

Test Gold Purity

If there is a chance you came across an item that doesn’t have a mark, it was probably made a long time ago when marks weren’t a legal part of the jewelry piece marking. Sometimes, it was removed during some additional work on the piece, like sizing the ring.

If you want to know about jewelry’s karats or want to check your piece of jewelry is true to the mark, you can test it. The best option is to find a jewelry shop that uses a non-destructive testing method. That way, you can be sure that testing won’t damage your piece.

Acid testing kit

One of the most popular ways is an acid testing kit. The procedure requires rubbing a part of the material over a grinding stone, then testing it with an acid. After its alloy dissolves, a jeweler can determine the exact karat and gold percentage in your jewelry.

Nowadays, you can find a professional testing kit available online to help you check the jewelry quality by yourself. However, visiting a professional is always a better option to prevent any possible damage.

Quick magnet test

When you don’t have enough time to do the proper gold purity test, you can rely on a magnet. Keep in mind that a refrigerator magnet is not strong enough, but the one from a local hardware store will do the trick.

If the magnet attracts your jewelry, you can be sure that it is not solid gold since this precious metal is not magnetic. However, many non-magnetic metals are used in costume jewelry, so this is only first-hand help, not final proof that you have a valuable piece.


  • EPNS – If you find this stamp on a piece of gold that someone tries to sell to you, you should know it stands for electroplated nickel silver or a silver plate. Hence, it is not true gold and certainly not worth much.
  • EPBM – Electroplated Britannia metal is a silver or tin alloy made of lead, copper, or zinc. It is not gold at all.

Gold Use

Gold Use
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Approximately 78% of the yearly gold supply is used for jewelry design, and 10% is necessary for financial transactions. However, there are a few common gold uses that will probably surprise you.

Cellphones and computers

Gold is an excellent conductor of electricity. Therefore, it is used in technology, even in cellphones and tablets.

Medical use

You have probably heard about golden drills, but gold is also a part of dental fillings and crowns. It is often used in medical appliances and instruments.


Gold is a valuable metal in the aerospace industry because of its qualities. However, it is served for this purpose mainly when the less expensive options are not available.

On the other hand, gold can protect astronauts from radiation in outer space. Therefore, astronauts’ suits are coated with a thin gold layer that can reflect the Sun’s burning heat.

Its reflective qualities are also used to stabilize the aircraft temperature. It serves as a coat since the dark-colored aircraft parts absorb more heat. Without an applied gold layer, a plane will break down faster.

Interesting Gold Facts

  • Almost all gold on the planet Earth came from meteorites that bombarded it approximately 200 million years after it formed
  • Since gold is not toxic, you can consume gold metal flakes in food or drinks
  • It is the only metal that is entirely yellow
  • It is possible to use gold as a lubricant in aerospace


Whether you buy gold jewelry for personal reasons, are a collector, or a jewelry seller, you should always look for the Karat Plumb mark on the desired piece. That way, you can’t go wrong with your investment. This stamp assures you that the exact value of the gold is never below the karat mark, but precisely that or even more.

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