Gold is a highly valued metal favored in making exquisite jewelry and is also considered a great investment. As you may know, gold being a precious metal doesn’t exist in its purest form. You’ll find it mixed with other metal alloys in most cases. This is done to improve its quality.
There are however different metals alloys used and they are mixed in different ways. This results in different gold alloys. To better understand how these alloys are formed, this post goes into detail discussing gold alloys and the mixing ratios used to form them.
Brief Introduction of Gold
Gold as a pure precious metal is highly malleable and ductile. Its elasticity on Young’s modulus scale is 79GP. That means gold’s elasticity is similar to silver but significantly lesser than metals like iron.
The scientific symbol for gold is (Au). Another fun scientific fact about gold is that it also has an atomic mass of 196.97 and an atomic radius of 0.1442nm. The number of protons in its nucleus is 79. This number of protons may be fixed but the number of neurons in each atom will vary with each gold isotope.
Brief Introduction of Gold Alloy
Given the softness of gold in its pure form, you will always find traces of other metals within it. This is because gold is alloyed with other metals to increase its hardness. This improves its durability as metal and makes it suitable in making expensive fine jewelry.
The common metals used in alloying gold are mostly silver, zinc, copper, and palladium. Depending on which of these metals are used and the ratio in which it is done, the resulting gold alloy will differ.
This is in terms of purity, texture, and color. Gold alloys with the least amount of gold are considered impure but tougher than the alloys with high gold content.
The alloys will also differ in color. The most common colors you’ll find will be white, yellow, and rose gold. Other colors like green and blue are also possible. Each colored gold is suitable for one or the other type of jewelry.
Caratage is the system of measuring the purity of gold alloys. While the weight is measured in troy ounces which are equivalent to 31.1035g, carats is the unit used to measure gold’s purity. In the US the most common carat you’ll find is 14 carats, and the least legally allowed purity is 10 carats. This is similar in most countries in the world. In some places, however, like the UK, France, Portugal, Austria, and Ireland, the least legally allowed purity is 9 carats, while in places like Denmark it’s 8 carats.
The number of carats can be denoted in decimals based on the amount of gold out of 24 parts. That is 14 carats, for example, means that the gold content is 14/24, which equals 0.583333. Hence the fineness mark of 14 carats is denoted as 583. In Europe however, 14 carats contain slightly more gold than 14 carats so you may find its fineness marking is 585. Similarly, 24 carats should have a fineness mark of 1000. It is however impossible to find gold that is 100% pure. There must be some slight traces of other metals. Hence, you’ll commonly find 24 carats fineness mark is denoted as 999.9. The tolerance when it comes to the purity of the gold will be based on the market. In China, for example, pure gold has a 1% negative tolerance for other metals, meaning the purest gold in china is considered to be 99%.
Additionally, the purity and fineness of gold can also be denoted by Karats. The initials K or Kt represent the karat system that uses karat numbers to denote how pure gold allows are. That means:
24K (24kt) is pure gold-containing 24/24 parts of gold, making it 100% of gold (although such purity doesn’t exist in jewelry.)
22K (22kt) is 22/24 parts of gold therefore it’s 91.67% of gold
18K (18kt) is 18/24 parts of gold therefore it’s 75% of gold
14K (14kt) is 14/24 parts of gold therefore it’s 58.3% of gold (or 58.5% in Europe)
12K (12kt) is 12/24 parts of gold therefore it’s 50% of gold
10K (10kt) is 10/24 parts of gold therefore it’s 41.7% of gold
Colored gold alloys are also considered real gold. They are simply a result of the metals added to gold. Yellow gold and copper which is red are the only two pure metals that are colored in gold alloys, the rest are either white or grey. While mixing gold with copper will give it a reddish tone, the white metals serve to make the gold paler.
The karat number of the gold alloy also affects the kind of color you get. The 6 parts of another metal alloy in 18k gold give enough room to play around with color. Lower karats are, however, better when you want to achieve a wider range of colors. This is because they have more room to include other alloying metals apart from the common ones.
Gold Alloy Formula.
As mentioned, the fineness mark is another way of expressing the purity of gold in parts per thousand. It is a representation of the gold content in jewelry. When it comes to the formula for gold alloy, the values vary based on the number of metals and gold content present. Aside from the common metal alloys that are zinc, silver, and copper, other metals may be included to create colored gold. The table below summarizes the formula of the different gold alloys based on karats and color:
Composition of Some Palladium Containing White Gold.
Normally, when making white gold, the alloy has to be plated with rhodium to get the desired white finish. That is when metals like platinum, zinc, and silver are used. When Palladium is used, however, there is no need for rhodium plating. Additionally, the white color does not fade over time as with rhodium plating. The table below summarizes the composition of white gold when palladium is included:
Other Facts About Gold Alloy Mixing Ratio.
When it comes to adding white metals to gold, the white metals act like bleachers that pale the color of gold. The strong bleachers are nickel, platinum, and palladium. Zinc and silver are considered moderate bleachers and any other white metals used are considered weak bleachers. As a result, there are two basic classes of white gold, that is, palladium whites and nickel whites.
For palladium whites, the primary use of the alloy is in jewelry making, where is commonly referred to as white gold. The palladium whites can, however, be used in dentistry. The addition of palladium to gold not only strengthens and hardens the gold but also improves its elasticity and melting point.
In some regions of the European Union, there is a higher demand for cheaper white gold alloys as opposed to nickel-free palladium whites. Some of these alternatives either contain low amounts of palladium or are completely palladium-free. The most common white gold alloy in such regions currently is the one that uses manganese as the main white metal. You could use metals like platinum, zinc, chromium, or iron as whiteners as well. Some, like iron, are more difficult to process, and all of them are poor whiteners compared to palladium. In addition, white gold alloys exist only up to 21k gold.
Also, keep in mind that by alloying gold, its physical properties are distorted. Using metals with larger atoms than gold, like silver, only moderately hardens the gold. Alternatively, smaller atoms like copper harden gold more efficiently.
When it comes to hardening gold to improve its durability, the method and result depend on what metal you use and the amount of gold you include. For different colored gold, you could play around with the different metal alloys until you get your desired result.
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