the colors of gold
Let's start from a fixed point, pure gold is bright yellow.
The reason why there are gold objects of different colors is given by the fact that gold is alloyed with other metals.
Why are alloys made instead of using pure gold?
The substantial reason is the extreme ductility of fine gold, it is in fact too soft to be durable in daily use; already around the middle of the seventh century BC in Asia Minor, by the Greeks of Ionia, the electrum was minted, a coin in a natural alloy of gold and silver.
The use of gold alloys gradually spread over the centuries, until it became common in medieval Europe for the production of coins and medals, but also to create valuable objects such as jewellery, reliquaries and liturgical objects. During the Renaissance, the use of gold alloys became even more widespread, thanks to the creation of increasingly sophisticated working techniques and the diffusion of new artistic styles.
Gold title and coloration
The fineness of the gold, or carat, indicates the quantity of pure gold present in the alloy in proportion to the total; I'll explain:
when the fineness of the gold is 750 (ie 18Kt), it means that out of 1000 parts, the alloy contains 75% pure gold and the remaining 25% consists of other metals.
In the graph we see a gray segment; it is precisely the metals that make up that segment that determine the color of the gold of the jewels we wear.
What are the metals used in the alloys?
Here are some general indications on the alloys commonly used to obtain golds of different colors:
Rose gold: to obtain a rose gold with a fineness of 750, the alloy can contain about 20-25% copper and the remainder silver and gold.
Red gold: to obtain a red gold with a fineness of 750, the alloy can contain about 5-10% copper and the remainder silver and gold.
Green gold: to obtain a green gold with a fineness of 750, the alloy can contain about 15-20% copper and the remainder silver and gold.
White gold: to obtain a white gold with a fineness of 750, the alloy can contain about 25-30% palladium or (nickel) and the remainder gold and silver.
NB Nickel was used before 31 March 2013, but, being a highly allergenic metal, its use in jewels was prohibited, the alloy used today allows you to obtain a slightly more yellowish white gold than what was obtained using nickel, to make it brilliant, a rhodium-based galvanic bath is carried out
Black gold: black gold can be obtained through a ruthenium-based galvanic process on the surface of the gold, without using other metal alloys.
It is important to remember that these percentages are indicative only and may vary based on the specific alloy and desired end result.
On the photo on the left we can see the color of the white gold trilogy that has just come out of the merger, in the center, that ring after the finishing and the rhodium-based galvanic bath (it's in my shop if you're interested); on the right there is a yellow gold ring with ruthenium bath limited to sapphire pavé (unique piece no longer available)
After these general notions, and above all after the photos relating to the rhodium-plated rings, I realize that I should open another chapter on the galvanic bath.
The next article will be on this topic