Jewelry FAQ: Click on a topic to learn more:

Au750 = 18-Karat

Au is the chemical symbol for Aurum, which means gold. Au750 indicates that 750 parts per 1000 (or 75 %) of an alloy are gold, the remaining 25% being composed of a mix of various metals. Another codification that indicates the same is 18-karat. 18 stands for 18 of 24 parts, or again 75 %, as being the contents of gold in a particular alloy. 18-karat gold is popular in fine jewelry and in Swiss watches, to a large extent because it is harder and more durable than fine gold. When the remaining 25 % of an 18-karat gold alloy consist of copper and silver, the resulting 18-karat gold color is more yellow. If the copper content is incrreased and the silver reduced, the color becomes more rose. If nickel, palladium, copper and zinc are added, the resulting gold color becomes more white. Lower gold alloys (not used by CADEAUX Jewelry) are Au585 (14-karat), Au375 (9-karat), and Au333 (8-karat).


Carat is a unit of weight measure used mainly for cut and polished or carved gems. 1 carat is equivalent to 200 milligrams or 0.2 grams. Carat as a weight measure should not be confused with the indicator of an alloy’s gold content (see: Au750 = 18-Karat Gold).


Some countries require that objects of precious metals be struck with a Hallmark, which makes the Hallmark’s owner accountable for the accuracy of the alloy indicated, say Au750, or 18-carat gold. Under Swiss law, Hallmarks are registered with and supervised by the state’s Precious Metal Control. Inaccuracies result in heavy penalties and bans. The Hallmark of CADEAUX JEWELRY is registered in Switzerland under No. 7949. By striking it into every piece of jewelry, CADEAUX JEWELRY guarantees the gold content as indicated. Pictured: CADEAUX JEWELRY inner ring band with registered Hallmark (symbolizing the 2Prong setting) and the 750 mark to indicate a gold alloy of Au750, or 18 Kt.

Hardness: Mohs Scale

Before technology grew more sophisticated, mineralogist Friedrich Mohs (1773-1839) developed a system of relative comparison of a substance’s hardness. He chose 10 typical substances of different hardness and ranked them from 1 to 10, depending on what scratches what. (Schumann). The Mohs scale is a popular measure. However, it is a stricly relative measure. Scales by Rosiwal who measured the intensity of grinding, and Knoop who measured the depth of an indent made by a diamond-pointed tool, are absolute scales of hardness. While they concur with Mohs’ relative ranking they show big differences in absolute hardness, especially for diamond.

Nickel Allergy

Nickel is a common metal often used in industrial production, including in white gold alloys, belt buckles, spectacles, costume jewelry, coins, buttons and batteries. Most people are sensitive to Nickel. Many have contact-reactions when skin touches Nickel: itching, rritation, even exzema. As a rule, symptoms will ease when Nickel is removed from the skin or when treated by a doctor. CADEAUX JEWELRY generally avoids nickel alloys and uses palladium or silver instead.

Specific Gravity of Precious Metals

All substances have a specific gravity or density, which differ from substance to substance. This means the weight of an object will vary depending on the material it is made of. The same item made of platinum will be heavier than the same item made of gold, similarly the same item made of gold will be heavier than the same item made of silver. The specific gravity of platinum is 21.45, gold 19.5, silver 10.5, titanium 4.55, aluminium 2.7, and water 1.0.

Treatment of Gems Codification

Gems and gem-rawmaterials are often treated. Some treatments are common and have been practiced for hundreds of years; others are more recent and often more controverstial. CIBJO – The World Jewellery Confederation has suggested that the following gem treatment be indicated on commercial documents:

N – No modification
H – Heating
O – Oil/Resin
W – Waxing
I – Impregnation
R – Irradiation
U – Diffusion
B – Bleaching
D – Dyeing
F – Filling
C – Coating
HPHT – High Pressure High Temperature


Sources: The information on this webpage, unless mentioned otherwise, is based on Edelsteine und Schmucksteine (Schumann, W., BLV Verlagsgesellschaft, München, Bern, Wien, 1976; referred to as “Schumann”), and Steine in Farben (Ostendorff, E., Otto Maier, Ravensburg, 1966; referred to as “Ostendorff”). Photos: CADEAUX Jewelry.