White Gold :: Low Copper Content Gold Jewelry : Karat (k) of White Gold : Palladium, Nickel

White gold is not a special form of gold. White gold is a true carat gold, just like yellow or red carat gold jewellery. They are gold alloys that look white rather than yellow.

Apart from copper, all other alloying metals to gold will tend to whiten the colour and so it is possible to make carat golds that are white in colour.

This has given rise to 2 basic classes of white gold:

• Nickel white gold
• Palladium white gold

White gold is created by increasing the silver-coloured alloys (zinc, silver, nickel, palladium) normally mixed with gold and decreasing the red-coloured alloy (copper). The white colour is achieved by careful choice of the alloying metals, which bleach the deep yellow of pure gold.

Additions of any white metal to gold will tend to bleach it's colour. In practice:

• Nickel and palladium (and platinum) are strong bleachers of gold.
• Silver and zinc are moderate bleachers of gold.
• All others are moderate to weak in effect.

White gold has become very fashionable in recent years, as many consumers have opted for the cool, contemporary white look over the classic yellow look.

A white gold setting can enhance the look of white diamonds and put a modern twist on a traditional standard.

White gold is an alloy of gold and at least one white metal, usually nickel, manganese or palladium. Like yellow gold, the purity of white gold is given in karat (carat).

For further reading on karat (carat, k, ct, kt) see Gold Grade :: Gold Grades by Humagaia.

White gold has properties that vary depending on the proportion of other metals used in a gold alloy mix. White gold alloys can be used for different purposes. A nickel alloy is hard and strong and therefore good for rings and pins. A palladium alloy is soft, pliable and good for white gold gemstone settings. Occasionally the gold alloy is mixed with other metals like copper, silver, and platinum to impart weight and durability. This is usually undertaken by specialized goldsmiths

The term white gold is used very loosely in the industry to describe karat gold alloys with a whitish hue. Most white gold is not truly bright unless it is rhodium plated. Most white gold products therefore have a coating of rhodium, to give a brilliant white appearance.

For further reading see Rhodium Plating :: Rhodium Plate by Humagaia.

Most people are under the impression that the colour of the rhodium plate, which is seen on many commercial pieces, is actually the colour of white gold. The term "white" covers a large spectrum of colours that border or overlap pale yellow, tinted brown, and even very pale pink / rose.

The jewellery industry often masks these off-white colours by rhodium plating. This is especially true where the secondary advantage of rhodium-plating is required - to cover an underlying nickel-gold alloy.

A common white gold formulation consists of 90wt% gold and 10wt% nickel. Copper often being to the nickel-gold alloy mix to increase malleability.

The strength of the gold-nickel-copper alloy is caused by the formation of two phases, a gold-rich Au-Cu, and a nickel-rich Ni-Cu. These two phases result in the hardening of the gold alloy material.

The alloys used in the jewellery industry are gold-palladium-silver (Au-Pd-Ag) and gold-nickel-copper-zinc (Au-Ni-Cu-Zn). Palladium and nickel act as primary bleaching agents for gold. Zinc acts as a secondary bleaching agent to overcome the colour of the copper metal.

White gold alloys for jewellery were originally developed in the 1920's as substitutes for platinum. They are commonly used in the jewellery industry for diamond setting, combination white / yellow jewellery items, and clasps (electroplated with yellow gold) for high-quality collars. This use is because they have high strength.

These white gold alloys have been used less than the coloured gold alloys in the past. However fashion moves on, and it is fashion trends that have been influenced by the increases in the gold price since 1972-1973. It is this increasing price trend (with a few blips in the middle) that has brought silver jewellery and white gold into prominence, especially in Europe.

White gold is usually an alloy containing 25wt% nickel and zinc. White gold is an alloy of gold and at least one white metal, usually nickel or palladium.

White golds are available:

• up to 21 carat.
• 18k white gold consists of 75% gold mixed with 25% white metals.
• 14K white gold contains as much gold as 14K yellow gold but is nearly white in colour.
• At the 9 carat (37.5% gold) level, a gold-silver alloy is quite white, ductile, soft and is used for jewellery purposes.

White gold has the same properties as yellow gold, but is mixed with different alloys to give it a white colour.

There is no legal definition of what constitutes a white colour for a white gold alloy. Basically, a manufacturer of white gold can get away with pretty much anything. However, if the customer does not like it then the manufacturer is stuck. Or is he?

A trade description of white gold may not mean 'detergent white'. Many commercial white golds are not a good white colour. The white gold alloys used in the jewellery industry are created by using a nickel or palladium alloy with zinc and copper. White gold alloys are based primarily on Au-Cu-Ni-Zn, and Au-Pd-Ag combinations.

The bleaching effect of nickel or palladium is a result of lowering the reflectivity of the alloy into the low energy part of the visible spectrum. Absorption processes become possible at energies considerably lower than for pure gold, and the reflectivity is reduced in the red and infrared regions of the spectrum.

White gold alloy is a soft metal which has a hardness of 2.5 on the Mohs scale, with a Vickers Hardness (VHN or HV) of 120. White gold has a melting point of around 240º C.

Nowadays, white gold is a jewellery metal in it's own right and currently very fashionable and desirable, particularly among the younger age groups. They are often used to enhance diamonds and other gemstones. White gold bridal jewellery is increasingly popular.

So, what does the manufacturer with off-white gold alloy do? I think you have guessed from the heading for this chapter.

Rhodium plating is where a thin layer of rhodium metal is electroplated onto a base of other metal. Rhodium plating is used to brighten the whiteness of otherwise less bright white material or to form a barrier between metal and your skin.

Rhodium plating is undertaken on various products that require a brilliant white finish. The rhodium plate produced is a thin layer of rhodium metal covering a substrate of a less white or non-white material. As for all plating, the plated layer can wear in time to reveal the underlying substrate. Rhodium plating is no different.

Where rhodium plate has been plated onto a white gold alloy the plated layer can be removed under heavy wear conditions. This causes colour discolouration due to the intrinsic yellow colour of gold. There is always a tendency for the 'white' gold alloy to have a distinct yellowish tinge. These gold alloy are frequently rhodium-plated to improve their appearance. Rhodium metal's chemical properties make it an ideal candidate for coating white gold jewellery.

A rhodium plate coating should be perfectly practicable for up to 3 years before it wears through to reveal the white gold alloy underneath.

See Rhodium Plating :: Rhodium Plate by Humagaia

Nickel allergy is caused when the metal nickel comes into contact with your skin and causes an allergic skin rash. An allergic rash, caused by the metal nickel, is usually a mild allergic reaction.

The main cause of these skin allergic reactions is the wearing of white gold alloy that has been created using nickel. The jewellery industry has gradually been moved away from creating white gold using nickel without placing a buffer zone between the actual white gold alloy and your skin.

The EU directive on nickel content only applies to the manufacture of nickel based articles produced within the European Union. Some white gold jewellery sold in the EU may contain nickel. It may, however, still conform to the EU Directive on nickel.

Japan and China took a similar position on nickel. The USA took a more relaxed approach, requiring jewellery to be labelled as nickel-containing. Many other countries have not taken a stance on nickel in jewellery and nickel white gold alloys are still widely sold.

See White Gold :: Nickel Allergy by Humagaia

Alternative White Golds

As palladium white gold is more expensive, there is a demand for cheaper alternatives that are nickel-free. Many new, patented alloys are coming to market, most of which rely on manganese additions as the main whitener. Some are palladium-free and others are low palladium alloys. They tend to be hard and more difficult to process. Many of these alloys are not a good white colour and require rhodium plating. They may suffer cracking and tarnishing problems too. Compositions of such alloys are not published.

Making gold white is similar to mixing concrete. The more grey cement you add to the yellow sand the lighter the grey-yellow mix becomes. But adding too much cement to get a lighter colour does more harm than good for usage of the concrete.

So, adding a red metal (copper) to a yellow gold will tend to make gold red and adding a white metal tends to make gold paler and eventually white. Thus, all other metals used to alloy with gold, apart from copper, will tend to whiten the colour. It is possible to make carat golds that have a reasonable white colour.

Additions of white metal to gold will tend to bleach the colour of the resultant alloy. in practice:

• Nickel and palladium (and platinum) are strong 'bleachers of gold.
• Silver and zinc are moderate bleachers.
• all others non-copper metals have a moderate to weak effect.

This has given rise, historically, to 2 basic classes of white gold:

• Nickel white
  The nickel-whites tend to have a colder white colour
  Good nickel whites tend to be hard and difficult to process.
• Palladium white
  The palladium whites have a warmer colour.
  Good palladium whites tend to be soft, easy to process (but lost wax casting is more difficult) but are much more expensive, because of the price of palladium.

Consequently, many commercial white alloys are thrifted in nickel or palladium and contain some copper. Because of this, colour is compromised. At the 8k to 10k (33.3% - 41.6% gold) level, gold-silver alloys are quite white and ductile, although soft. They are used for jewellery purposes.

White gold alloys can be classified into four groups,

1. Nickel-based white golds (76%)

2. Palladium-based white golds (15%)

3. Nickel-free and palladium-free white golds (7%)

4. Nickel + palladium white golds (2%).

Nickel-gold based white gold has long been the most commonly used white gold alloy for white gold jewellery production.

There are many reasons why nickel metal has been the preferred metal in the production of white gold alloys.

There are many reasons why nickel metal has been the preferred metal in the production of white gold alloys.

White gold nickel-gold alloys containing between 3.5wt% and 5wt% of nickel metal have excellent mechanical properties. Due to the off-white nature of these lower nickel concentration gold alloy there is a requirement to whiten the resultant white gold alloy with a final rhodium plating.

Zinc is used in gold-nickel white gold alloys as a secondary bleaching element. The zinc metal is added in order to compensate for the darkening colour effect of copper.

Nickel white gold alloys are utilised for all standard karatages of white gold from 8k to 22k. For the lower karatages there is a substantial requirement for copper and zinc in order to maintain good mechanical properties

See Nickel Gold by Humagaia

White gold palladium-gold alloys have a warm white-grey colour which has proven to be very appealing. Palladium-based white gold has limited hardness and has good workability.

Mechanical characteristics are widely divergent due to their palladium content.

Most of these alloys are based on the gold-palladium-silver system and the metallurgical behaviour depends on the characteristics of the gold-palladium (Au-Pd), gold-silver (Au-Ag) and palladium-silver (Pd-Ag) systems.

Palladium prices have risen steadily. This has restricted the utilization of palladium-based white gold alloy. Only the high end of the gold jewellery market has access to palladium-based white gold alloys, other than for nickel-free hypoallergenic earring manufacture.

See Palladium Gold by Humagaia

White gold containing both nickel and palladium has decreased in popularity due to the high cost of palladium. Some nickel-based white gold alloy contains palladium.

Some palladium-based white golds also contain small additions of nickel

At a concentration of 5wt% all alloying elements show good workability except gold-titanium.

Nickel free white gold is the requirement.

For white gold, alloys which contain neither nickel nor palladium, are actively sought. However, satisfactory substitutes for nickel and palladium are proving difficult to come by.

When we come to the need for a substitute or substitutes for nickel and palladium for the production of white gold alloy we hit upon an impasse. It seems that all substitutes have one or more, not inconsiderable, property problems.

Apart from the usual and expensive suspects of silver (Ag) and platinum (Pt), the current candidates for the nickel-free, palladium-free white gold alloy are:

• Iron (Fe)
• Indium (In)
• Manganese (Mn)
• Chromium (Cr).

See Nickel Free White Gold by Humagaia.

18k white gold alloys have been developed as a less expensive substitute for platinum alloys. Not only are white gold alloys less expensive, they also give other advantages in comparison with platinum:

• Higher strength
  
• Much lower melting temperature
• Higher fluidity.

These characteristics are all very important for their use in lost-wax casting. It is well known that:

• Gold and copper are the only coloured metals.
• All other metals are white or grey (gray).
• Nickel and palladium are the most important bleaching elements for 14k and 18k gold alloys.
• In 8k, 9k and 10k gold, the addition of silver also gives a good bleaching effect.
• Alloying gold with other metals will also give some whitening effect, but much lower effect than by palladium or nickel.

Moreover, these alloys do not usually show the physical or mechanical characteristics required for their use in lost-wax casting. In addition, they only can be used for casting under vacuum conditions with graphite-free crucibles.

Colour is a most important property of an alloy for jewellery. Below you will find a section summarising the basic colour concepts and its measurement, as it has been defined by the CIELAB system.

Presently, lost wax casting is used extensively for gold jewellery production. Its use for white gold production is growing strongly.

The use of silicon-containing and boron-containing alloys has been employed for many years

Advantages of the use of silicon-containing alloys:

• Clean surfaces with very indistinct oxidization layers.
• High fluidity.
• Strong capability in filling moulds.
• Low surface roughness.
• Higher resistance to oxidation.

Disadvantages to the use of silicon-containing alloys:

• Increased brittleness in 18k to 22k yellow gold,
• Increased granularity,
• Grain boundaries show segregation.
• There is a possibility of reaction with other alloying elements.
• There is a possibility of reaction with white gold impurities.
• Hard spots may form.

In lost wax casting, the use of grain refiners is also extensive. These have developed only recently with any success. This success is due mainly to the use of vacuum melting and casting machines.

These alloys are suitable for pieces with an extended surface. They are also suitable for heavy items.

The advantages of grain refiners are:

• Solid surfaces,
• Improved ductility and other mechanical properties.
• Reduced grain size.
• Reduced shrinkage porosity.

The disadvantages of grain refiners are:

• Presence of surface oxidation.
• Slight increase of hardness.
• Low fluidity.
• Low capability for filling moulds,
• Grain boundary segregation.,
• Formation of clusters or hard spots.

A common type of inclusion are nickel silicides. These can originate from the master alloy. They can also form in 18k molten alloy. Hard spots are irremovable spots in the ends of cast pieces.

Methods have recently been developed that enable a quantitative and objective evaluation of colour. These techniques can be employed in the analysis of the colour of jewellery, particularly for white gold alloys.

The CIELAB method is available for jewellery production. With this method, colour is represented by colour intensity and luminance (brightness),

Colour measurements on gold alloys the CIELAB method are accurate and consistent. This is an important step forward for objective characterization of precious alloy colour identification.

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