Alloys and Karats and Colors Oh My!

Considering how long humans have been working with metals, you’d think there was nothing new to discover under the sun about them. But the art and science of creating alloys and using those alloys to create beautiful new objects continues to engage the imagination and experimentation of craftspeople all over the world.

One of the most exciting things about making jewelry is the opportunity to work with metals. Metallurgy is one of the oldest material sciences in the world, dating back to when gold was discovered as early as 40,000 BC. Silver, copper, tin and meteoric iron are known to have been used by early cultures for rudimentary smelting in the 5th and 6th millennia BC, including a copper axe that was created around 5,500 BC. 

Considering how long humans have been working with metals, you’d think there was nothing new to discover under the sun about them. But the art and science of creating alloys and using those alloys to create beautiful new objects continues to engage the imagination and experimentation of craftspeople all over the world.

Changing the Color of Gold

One of the most fun things to do with metals is to experiment with color. Gold is a particularly fun metal to play with, because it is highly malleable in its pure state and it responds well to alloying with other metals. 

The most common alloying metals for gold are silver, copper, and zinc. For instance, 22k yellow gold is actually made up of roughly 91.67% gold, 5% silver, 2% copper and 1.33% zinc (all formulas in this article will be approximate, as different jewelers will slightly vary percentages. So we are just sharing the most common here). But what if you wanted an 18k red gold? Then you might discard the silver and zinc, and go with 75% gold and 25% copper. If you prefer a softer red - an 18k rose gold - you would reintroduce silver, for a formula of 75% gold, 22.5% copper, and 2.5% silver.

You’ll notice that in the 18k gold colors, the percentage of gold has remained at 75%. That’s because to achieve each karatage you must have a specific percentage of pure gold. Karat (or carat outside North America) is defined as the measurement of the ratio of gold to other metals or alloys. Karats are measured on a scale from 0 to 24, and the higher the karat number, the more gold that is present in the mixture.

Gold Weight Rules and Hallmarking

The rules around karatage (or hallmarking) are governed by the National Gold and Silver Stamping Act in the United States, and other countries have similar regulations. According to the  MJSA website (https://www.mjsa.org/publications/compliance-guides/marking-stamping-regulations), “Violating the act can mean forfeiting merchandise, paying monetary penalties, and serving jail time. It also allows competitors and jewelry trade associations to bring lawsuits against any violators.”

To remain in compliance, it is essential that you have the minimum percentage by weight of gold allowed for each karatage claim. The following chart - as found on the MJSA Website - shows gold purity requirements along with solder tolerances, showing you just how specific the regulations are regarding gold purity!

 

Karatage

Minimum % of Gold Weight

Tolerance (% weight) without solder

Tolerance (% weight) with solder

Minimum % of weight of gold allowed with tolerance, without solder

Minimum % of weight of gold allowed with tolerance, with solder

24K

99.95

0.3

0.7

99.65

99.25

18K

75.00

0.3

0.7

74.70

74.30

14K

58.33

0.3

0.7

58.03

57.63

10K

41.67

0.3

0.7

41.37

40.97

Of course, you have more karat options than these. Here’s a purity conversion chart for all karats from 9 to 24:

Number of Karats

% of Gold Purity

9k

37.5%

10k

41.7%

12k

50.0%

14k

58.33%

18k

75.0%

22k

91.7%

24k

99.95%



The FTC Jewelry Guides are similarly specific when it comes to gold claims related to plating, vermeil and gold filled. There are steep penalties for misrepresenting the karat fineness, thickness, weight ratio, or application method of a product’s coating or filling. The guides further specify that you cannot deceptively use the terms “gold filled,” “gold overlay,” “rolled gold plate,” “gold plated,” or any abbreviations thereof unless the plating or filling has minimum thicknesses or weights as defined by the Jewelry Guides.

The main takeaway here is that it’s critical you get your metal weights correct when hallmarking and naming your gold items. More than one jeweler has gotten in trouble because they melted a client’s 14k gold ring, added a few pennyweights of gold to get to 18k, hallmarked it as 18k, and later found out they fell short of the gold weight percentage requirement. So either get really good at creating alloys by following the math and testing everything, or buy your alloys from a reputable supplier. 

More Gold Colors

But let’s get back to colors (the fun stuff)! We already shared the common alloy recipes for 22k yellow gold, 18k red gold and 18k rose gold. What are some other common alloy recipes?

  • 18k pink gold: 75% gold, 20% copper, 5% silver
  • 18k white gold with platinum group metals: 75% gold, 25% platinum or palladium
  • 18k white gold: 75% gold, 17% nickel, 8% copper. Replacing some of the nickel with zinc is usually required to achieve optimum results.
  • 18k soft green gold: 75% gold, 25% silver

We said it before, but it bears repeating: All of the percentages we’ve shared in this article are just examples of commonly used recipes for the purpose of illustrating alloying concepts. If you want to try your own hand at alloying, be aware that trial and error are the norm! At David H. Fell & Co. we have spent years perfecting our alloy recipes, and we use highly controlled production processes to make sure they come out the same way every time. Experimentation with alloys can be great fun, but don’t expect to get perfect results the second … or even the ninth! … time. Producing your own alloys can be a wonderful way to deepen your knowledge of metals and see how they behave (or not) as you turn them into jewelry. But for production purposes, you’ll probably be happier, work faster, and save money if you buy metal with proven performance characteristics.

The art and science of creating alloys has entertained alchemists, artisans, material scientists, and jewelers throughout the ages. It’s just one of the things that makes being in the jewelry industry and creating jewelry so much fun.

Is it the Same in Silver?

Most jewelry buyers are familiar with fine and sterling silver, but there are more types of silver than these!

If you have any antique silver jewelry or flatware, you may find it stamped as 800. 800 Silver, sometimes also referred to as “International Coin” or “Spring” Silver, was very common in Europe but not in the United States. If you have some in your collection, you probably inherited it from a European ancestor or bought it at an antique shop. These pieces are 80% pure silver and 20% other alloys (often, but not always, copper). Let’s take a look at a table of common silver alloy recipes:

Type % of Silver Purity Other Metals
Fine 100%  
Britannia 95.8% Usually copper
Mexican Silver Standard 95% 5% copper
Sterling Silver 92.5% 7.5% copper. May include zinc, nickel. germanium, silicon, platinum or boron, but 7.5% copper is most common.
Coin Silver 90% Nickley, aluminum, and copper have all been commonly used for the remaining 10%.

There are many other patented and branded alloys of silver. One that comes to mind is Precium, which was patented by now-defunct metal company Handy & Harman in 1974. This metal was 74% silver, 25% palladium, and 1% indium. It was known for being very heavy and tarnish resistant. It was also too expensive for most commercial applications of silver. Another more well-known proprietary alloy is Argentium, a patented silver alloy designed to be tarnish resistant. The Argentium patent covers alloys that are 80% - 96% silver, 0.1 - 5% germanium, and 1-19.9% copper.

Scrap and Hallmarking

As you can see, there are a lot of ways to alloy gold and silver (and we didn’t even get into platinum group metals yet!). Alloying is an exciting part of being a jeweler, because every time you mix alloys you change both the working dynamics and the appearance of the metal. But you also must be very careful, because that finished piece will require a hallmark - a claim - and that claim must be accurate.

Jewelers often get into trouble when asked to remake a piece of heirloom jewelry using the original metal, or when they decide to process their own scrap. You can certainly melt your own scrap, but it’s not as simple as taking a torch to it or popping it in your casting machine. 

First of all, fabricated metals usually have solders in them, and solder residue melted with the metal will interfere with alloying. So if you melt your own scrap, you must cut apart the areas where a ring has been sized or a head has been soldered on before you melt the metal.

Second, as you can see from the charts above, fabricated metals have a lot of different alloys in them. Each of those alloys contribute different properties to the final hardness, ductility, malleability and appearance of the metal. If you’re not sure which metals are in your alloy, you could end up with an alloy that cracks, has excessive porosity, or simply looks dingy. So using the proper melting methods is essential for removing and reducing impurities and deoxidizing the metal. Finally, get out your calculator, scale, and a great reference chart to make sure you add in enough pure new metal to bring your alloy to the proper karat standards.

This is the main reason that most people send scrap to a refinery partner (like us!). The time and care it takes alloy your own metal ends up costing more than the fee you pay to outsource it, and outsourcing your scrap also gives you protection related to FTC and international requirements for metal purity claims.

So … next time you have a bit of extra time in the shop with some gold or silver scraps laying about, why not try out a few alloy recipes yourself? You’ll probably find it too time-consuming to do on a regular production basis, but it’s a great way to experiment with metals and become more familiar with their properties.

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