Today we will talk about the quality of gold and its composition.
Gold is a very soft material that has a Mohs hardness of only 2.5. Pure gold (99.99%) is softer than tooth enamel, so it is easy to scratch.
An interesting fact:
Ancient traders used to try a gold coin “on the tooth” to distinguish it from a fake.
A genuine gold coin left a small dent when bitten and did not have a specific flavor, such as copper, like counterfeit coins.
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Jewelry made of pure gold is not suitable for everyday use because it is fragile, flexible, and easily breaks and scratches. That is why other metals are added to gold to make it harder – ligatures.
The percentage of impurities added to gold determines its grade.
The grade shows how much pure gold is in the alloy.
The highest 999 grade is precious metal, gold without impurities (99.9% gold).
There is a carat and metric system of gold assays.
Carat grade
The oldest and most widespread in the world is the karat (Karat).
* A carat in a gem is denoted by the letter “C” Carat.
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An interesting fact:
People used to take plant seeds as the equivalent of weight. For example, the ideal of weight in the Roman Empire was the evergreen carob tree, which is often found in the Mediterranean (Ceratōnia silīqua).
Its pods contain beans weighing 0.2 grams each. The measure was named “Siliqua” from siliqua (bean), and it later became known as “Carat” (from Ceratōnia).
How did the “bean carat” become the standard for gold purity?
In 309, Emperor Constantine I began minting coins of the purest gold weighing exactly 24 Silicas (or 24 carats). Because of their consistently high composition, they were considered the most prestigious. And so began the history of the karat gold standard.
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While in gemstones, carat means the weight itself, in gold it is the ratio of gold to impurities. In other words, how many parts of pure gold are contained in 24 parts of an alloy.
In total, there are five options in the karat system: 9, 10, 14, 18 and 24 karat gold.
And the highest grade of 24 carats means 99.9% gold.
For example, 14 karat means 14 parts of pure gold and 10 parts of other metals.
Dividing 14 by 24, we get 0.58333 or 583 assay.
The grades correspond to the following table:
24 K or 999 assay – 99% gold
18 K or 750 grade – 75% of gold
14 K or 583 samples – 58.3%.
10 K or 417 grade – 41.7%.
9 K – the lowest, 37.5%.
Metric sample
In the post-Soviet countries, the metric sample system has been adopted since 1927. These are the familiar 999, 750, 583, 500 and 375 samples.
The only exception is that in 1994, the 583 standard was changed to 585 (containing 58.5% pure gold) for convenience.
By the way, 585 is the most practical!
On the other hand, the higher the gold content in the alloy, the less it is subject to oxidation and darkens.
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An interesting fact:
Our 750 and 585 grades are inferior in strength to the European 18K and 14K grades.
This is because more soft copper is added to the ligature (impurities) of our gold, while the European standard contains more silver.
Now do you understand why we have gold with a reddish tint, while in Europe it is yellow?
