Meaning of 24 karat gold purity
Gold is the most valued precious metal in jewelery, much more than platinum.
French demand for solid gold jewelry is 6 times larger than for platinum jewelery.
Given the respective prices of these precious metals, the purity index in gold - or platinum - alloys used in the manufacture of jewelry has a significant impact on the price of these.
Their purity is expressed in carats (historical measure) or in thousandths (official measure for France).
14k rose gold chain hallmarked (14KT) in USA,
in France, the punch would be "584"
Be careful, do not confuse the carat of jewelers used for diamond which is a unit of mass used to measure gems.
One carat (diamond) equals 0.2 grams, the karat of jewelers indicates the proportion of pure metal in the alloy of gold, platinum or silver used for the manufacture of jewelry.
One karat of jeweler is equal to 1/24° of the total weight of alloy considered.
Practically, for a jewel in 18 karat gold still officially called 750 thousandths, that means it consists of 18 parts (mass) of pure gold and 6 parts of another metal.
As you can see, this karat of jewelers is an old way of expressing the percentage of a precious metal in an alloy.
Ancient origin of the word "carat"
The etymological origin of the carat of the jewelers comes from the word "Quirat" which is an old term of navy expressing the part of property of a ship when this one belongs to several people.
The ship is subdivided into 24 parts of equal value (one quirat) and each owns a number of quirats, expressing the percentage of the boat's shares (source).
Why combine gold with other metals?
Gold coins and metal shot used to prepare rose gold.
As with all alloys, the goal is to improve the properties of the base metal.
Gold is a noble metal, that is to say, it resists corrosion and does not oxidize with water or air (so its yellow glow persists), what is more, it is ductile, so it's easy to shape.
The disadvantage is that in its pure state, it does not withstand mechanical stresses well.
Therefore, a jewel in pure gold (24 carats) that would be thin, would be easily deformed during a false movement or shock.
It is for this reason that it is combined with other materials that will give it superior mechanical strength without altering its other advantageous physical properties (noble and ductile material).
Thus, 18 karat gold (75% of its pure gold weight) is the most valuable solid gold alloy used in conventional jewelry.
14 karat gold (58.4% of its weight of pure gold) is the most common because it is much more affordable than 18k gold while keeping a yellow color very close to this latter.
Finally, 9 karat gold (37.5% of its pure gold weight) is the most affordable gold alloy on the jewelery market.
Equivalence between thousandths and karats of gold titles
Hallmark for 22k gold parts marking
Here is a table showing all the titles of gold, most are theoretical not at all or very little used in jewelry.
This graph explain the 24k of gold in purity percentage
The carats of gold in bold are those that are the most used in France and recognized as the legal titles.
In jewelery will find mainly 18K gold, 14 and 9 carats jewelry in France.
Other countries use 10-carat gold instead of 9-carat gold (notably the USA).
For jewelry in 20k gold or 22 karats, you should contact a jeweler to make these jewelry on demand as for this example of a 22k gold pendant.
22k gold cross pendant
Clarification on pure gold
A piece of pure Canadian gold made of 24 karat gold with a purity grade of 99.999% gold. If the indication on the coin worth $ 100,000 is symbolic (it is worth at least three times more), it weighs well 10 kilograms.
100% pure gold does not exist.
The term pure gold is relatively vague since it is given to bullion whose purity of gold is at least 99.5%.
It should be noted that 99.99% pure gold was first produced in 1979 by the Royal Canadian Mint.
Modern techniques currently allow the production of gold with a purity of 99.999% also called gold 5-9, however, only the Royal Canadian Mint is able to produce gold as pure now.
Read this PDF sheet explaining the gold refining process put in place to achieve this degree of purity.
The physical properties of gold
Evaluate the karats of gold without the punches
18k white gold signet ring with diamonds and onyx
If French law (other countries' law as well) makes it necessary to mention the title of the gold of a jewel with the help of a stamp, it is often necessary to evaluate in a concrete way the title of the gold .
As well to resell a jewel in the case of an individual, or simply if you want to repair or modify it in the case of a jeweler.
Indeed, the welding of a gold object requires using the correct title of the metal to achieve the welding.
A filler metal with a lower gold title is used for soldering to the gold title of the jewel. Typically, to weld an 18 karat gold jewelry, 16 k or 14 karat gold will be used.
When reselling gold to quantify the transaction, both parties (buyer and seller) ensure the quality of the gold traded by chemical analysis or electronic measurement.
In the first case, a gold test kit is used which includes bottles containing aqua regia at different concentrations and then the touchau test is carried out.
Or we use an electronic device that tests gold using an electric current, as shown in the following video (to read on the subject).
Gold testing with RS Mizar device