Precious Metals - Pierre DeRoche PDR 4020 Mode D'emploi

Colour
Several grading scales are used, some of which are local, and they are
linked between themselves by correlation tables. Among the most
widely known is the "GIA" (Gemological Institute of America) scale
ranging by decreasing quality from the letter D (absence of colour) to
the letter V (yellow colour). The "Old Terms" scale is internationally
recognised and is the most commonly used. Stones are classified,
by decreasing quality, according to the following terms: River
(Exceptional White), Top Wesselton, Top Crystal, Crystal, Top Cape,
Cape, Light Yellow and Yellow

Precious metals

The precious metals most used in watchmaking and jewellery are gold
and platinum. Gold has the specific property of being unalterable, as
well as malleable and ductile (meaning it can be drawn out without
breaking). Gold is not used in its pure state (999.9/1000 or 24-carat
standard of fineness), but is instead alloyed with other metals so as
to lessen its malleability and to modify its colour.
The gold alloys used in watchmaking and jewellery are thus composed
of 75% gold and 25% other metals.
These other metals are copper, silver and palladium, in proportions
varying according to the desired colour.
• Yellow gold: 75% gold, 16% silver, 9% copper
• Rose gold: 75% gold, 5% silver, 20% copper
• White gold: 75% gold, 4% silver, 4% copper, 17% palladium
As far as terminology is concerned, the word "gold" is reserved for
alloys with standards of fineness corresponding to 0.916 (22 carats)
and 0.750 (18 carats). As for platinum, the alloy used in watchmaking
and jewellery is composed of platinum (95%) and palladium (5%).
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