Pure 24 carat gold being too soft to make jewelry, it is mixed with other metals to "harden" it. 18 carat gold means that of the 24g of alloy, 18g is "pure gold" which is 75.01%. It is also called 750/1000 gold.
9 carat gold means that of the 24g of alloy, 9g is "pure gold" which is 37.5%. It is also called 375/1000 gold. 18 carat gold therefore contains more fine gold per gram than 9 carat gold.
375/1000 jewelry is precious gold jewelry. It has been sold for many years in different European countries, including France. The returns for 375/1000 jewelry are no more numerous than for 750/1000. Like with 750/1000 jewelry, it should be taken to your jeweler so that they can restore its brightness and brilliance, after a few seasons.
The difference in price between 375/1000 gold and 750/1000 gold can be up to 30%. There is less fine gold in 375/1000 jewelry, 38% compared to 75% in 750/1000 jewelry. The total weight of the same jewelry is lighter in 9 carats than in 18 carats, the gold being the heaviest metal in the alloy. The price depends on the quantity of gold in the alloy as it is the most expensive metal. 9 carat gold therefore costs less than 18 carat gold per gram. The alloys used in 375/1000 jewelry are also precious metals (silver) so these components are long-lasting. However, the price of diamonds and the work done by workshops stays the same for 9 and 18 carats.
The composition of the 375/1000 gold alloy does not mean that 375/1000 gold is more fragile and more delicate than 750/1000 in any case. The size measure for 375/1000 rings are made in the same way as 750/1000 gold rings.
The 375/1000 alloy being made of more copper, you must of course avoid contact between oxidants and this jewelry which could be altered more quickly than 750/1000 gold. Nevertheless, all gold jewelry has usage precautions.
The yellow and white hues of the 2 alloys are codified to ensure a regularity of color. All yellow 375/1000 gold jewelry is covered in gold flash to harmonize and homogenize the color and to maintain it throughout time. It is possible to re-flash yellow 375/1000 gold jewelry to maintain it and give it back its maximum shine.