GOLD: karatage and gold colors

If you are not familiar with the gold business, you might be confused about gold, karatage and gold colors.

People who come in my jewellery shop, very often ask me the same questions about the gold items, in this article I would try to answer two of the most common questions and give more information about this metal:

“what does it mean the 750 that is stamped on gold jewellery?”

Gold is a noble metal but is not used pure in jewellery: it’s too soft to be worn without been damaged. A jewel made of pure gold would lose its original shape in short time, not mentioning the surface that would be full of scratches. 

This means that what we buy in shops are actually items made of an alloy of gold mixed with other metals. According to the percentage of pure gold inside the alloy, the item is stamped with its “karatage” which is a number (or symbol) that tells, out of 24, how much pure gold is present.

One karat (K or Kt) is 1/24^th part of a unit of gold. Therefore, if the gold is pure it is 24 Karat. 

Karat	Parts of pure gold out of 24	%  of actual gold in the item	stamp
24 Kt	24/24	99,99%	1000
22 Kt	22/24	91,67%	916
18 Kt	18/24	75%	750
14 Kt	14/24	58,5%	585
12 Kt	12/24	50%	500
10 Kt	10/24	41,67%	416
9 Kt	9/24	37,5%	375

Most Countries choose to make jewellery in 18 karats. If you have home some gold jewellery try to check it under magnification, somewhere you should be able to fine the inscription that tells which karatage it is. For 18 karats the inscription is either “750” or “18K” and usually they are followed by the logo or code of the manufacturer company that guarantees the karatage.

18K is an alloy where 6 part out of 24 are made of metals that allowed gold to be hard and tough enough to be worn and hold safely the gemstones.

If under magnification you can’t find any inscription, or the number you can see is not 750, there might be several explanation:

•            Maybe it was made in a Country, or a time, where the stamping was not mandatory.
•          If it’s stamped with 925, it might be silver.
•          A karatage different than 18K has a different stamping, check the chart above.

Nowadays is possible to see shops that sell items with any kind of karatage. The constant rise of the price of the gold made jewellery less affordable, so a low karatage imply less pure gold in the alloy, which means a lower cost.

“What is the difference between white and yellow gold? How can we have more gold colors?”

 Gold, naturally, forms only in the yellow color, but very often we see jewellery collection made of gold in different colors, how is that possible?

As we mentioned before, gold is not used pure in jewellery, but is mixed with other metals in an alloy that can modify the original yellow.

White gold is very appreciated worldwide; this alloy was invented after the First World War, there is a strong presence of silver and palladium that lighten the original color giving a whitish look.

The color is actually more grey than white: at the end of the making process, the item is coated with a thin layer of rhodium that gives the same look of platinum. The only problem: after some time, the layer can fade showing again the yellowish color underneath,  which can be covered with a new layer of rhodium.

Rhodium, palladium and iridium belong to the platinum group; the use of rhodium for platinum plating is very common in jewellery to achieve a whiter finish, especially to plate white gold and sterling silver.

In all this “colored” items the karatage is always guaranteed from the manufacturer company, so if in a 18K jewel we want to see different colors we just have to change the other metals of the alloy:

Yellow	75% pure gold	12-7% Silver	13-18% Copper
White	75% pure gold	25% Nikel, Silver or Palladium
Pink	75% pure gold	6,5-5% Silver	18,5-20% Copper
Green	75% pure gold	12,5% Silver	12,5% Copper
Red	75% pure gold	4,5% Silver	20,5% Copper

The percentage in these recipes may vary according to the final project, the factory or the rules of the Country where is made.

To make blue gold the process is slightly different: Iron is mixed in the alloy with gold and after is exposed to heat to oxidize the iron atoms on the surface, which produce a bluish coloration.  

Malachite

Malachite is a green opaque gem. It crystallize in the monocline system.

The name comes from the Greek MALAKE’, that means mallow, of which it has the color of the leafs. Its main characteristic is the curved bands pattern in several green tones, from light to dark one. the color is given by the main component, copper, in the past it’s used to be found in deposits near to this metal. Thanks to its colour is considered the gem symbol of hope, love and faith.

 

The hardness is 3 and a half on the Mohs scale and, because sometimes it is found in big blocks, is quite often carved to get cameos, art crafts and statuettes.

The toughness is quite low, that’s why it must be handled with care. It can be ruined by chemicals, especially acids. It is also quite sensitive to heat and hot water.

In the past the main source of Malachite used to be Russia, but now new deposits are in Africa, Australia and USA. The best samples come from Shaba, Kenia.

Sometimes is found along with the stone Azurite; the match create a stone called Azurmalachite.

In nature it is found in microcrystalline clusters consisting of fine needles. The exact scientific term that describes its natural form is Botroydal, which refers to its irregular nodules growth in concentric layers, which, once cut, show the banding pattern that characterizes it.

Historically, it has always been a popular gemstone since the ancient Greeks and Romans, who used it for carvings and ornaments that we can still see today. In Latin culture it used to be associated with the Goddess Venus, they believed it can help to reunify lovers and also console those who have lost their loved one.

Was also used as an amulet to protect the owner from danger and especially to protect children, since the time of Solinus it was suggested to put it directly in the cradle of infants; also, to be placed near the woman womb to support conception and childbirth. According to ancient beliefs it  could be pulverized and dissolved in milk to help with heart disease, or mixed with honey and applied to wounds to promote healing.

When  in the 18th century rich deposits were found in Russia, the mineral became the favorite ornamental stone by the court of the Tsar. An example of this are the great pillars of the church of St. Isaac in Leningrad.

Malachite is considered a semi-precious gemstone and maybe this is the reason why nobody never created a synthetic version, but in the market there are many other cheaper alternatives, such as plastic, glass or dyed agate.

The only type of treatment that is applied to enhance the appearance is the impregnation with mineral oils to make the surface shiny and smooth.