Before you read this, we recommend reading our general introduction to Gold alloys and an introduction to phase diagrams.
White gold for jewelry was originally developed as a substitute for platinum and is currently particularly popular. Pure Gold has a yellow color, but by alloying with other elements, we can dramatically change the color of the alloy.
Typically we alloy gold with copper and silver, but white gold alloys are typically Gold-Nickel and Gold-Palladium alloys. Palladium and nickel are strong bleachers of gold; silver and zinc are moderate bleachers, while other metals have a moderate to weak effect.
Note there is a limit in the karatage range for white golds up to 21K (<12.5 wt.% Pd). It is currently impossible to make a 22K white gold because the available 8.4% of alloy additions are insufficient to give a good white color.
The difference between Nickel and Palladium
In the US, nickel is used as a primary whitener of gold. However, its metallurgy with gold is difficult, with very limited solubility of nickel in gold – Nickel would much rather form a second phase than sit in the gold lattice. This is known as an immiscibility gap.
Two-phase alloys are hard but far less ductile and difficult to work with. Those working with nickel-white gold are well aware of its many difficulties.
Palladium has extensive solubility in gold alloys, and so forms soft, ductile alloys. They are considerably softer and easier to work than nickel golds. This makes them useful for gem-setting purposes.
Additions of 10–12% palladium to gold impart a good white color, but palladium is an expensive metal, and the alloys are denser than nickel ones (pieces of equivalent size are heavier – containing more gold). In addition to their high cost, gold-palladium alloys have higher melting points.
Ag / wt.%
Pd / wt.%
Cu / wt.%
Ni / wt.%
Zn / wt.%
Hardness / HV
Liquidus / ˚C
Rhodium Plating of White Gold
Commercial Gold–Nickel alloys tend to be low in nickel content, so they also contain silver and zinc to obtain whiteness. Copper is also added to improve workability.
The low nickel and the copper result in a yellowish-brown tint to the white color. Such poor-color white golds are often rhodium-plated to give a good, tarnish-resistant white color that should last for some years before the coating wears away.
Many commercial palladium-white golds contain only about 6% to 8% palladium, with additions of silver, zinc, copper, and even some nickel, in an attempt to keep the cost down. These alloys have a less satisfactory white color and will often be rhodium-plated, experiencing the same problem as nickel-white golds.
Legal restrictions and skin rashes
Nickel-based white gold alloys are cheaper, but nickel is a skin-sensitizing element and so is known to cause a skin rash. European legislation means nickel-rich alloys have been phased out, although low nickel (<6 wt.%) contents are still legal.
Commercial alternatives to Nickel and Palladium
With the high cost of palladium, alternative white golds have been developed. These often contain manganese and other metals such as iron and chromium. There are several problems:
They are difficult to work and cast.
They tend to crack.
They often tarnish.
A poor white color requires rhodium plating.
Commercial white golds can vary significantly in their degree of whiteness. To quantify their witness, there are agreed definitions of "whiteness" using the Yellowness Index.
The key points are as follows:
White gold has a white color due to the bleaching effect of alloying additions, namely Nickel and Palladium.
Nickel White-golds can often cause skin rashes.
Palladium White golds do not cause skin sensitization and are easier to work with but are far more expensive and softer than nickel-based white golds.
White golds can often be rhodium plated to ensure a bright-white appearance. This effect is limited as the plating can often wear away.
The whiteness of an alloy can be quantified using the Yellowness Index.
Cover image: White Gold Ring courtesy of Mark Adwar.