Palladium Gold :: White Gold with Palladium :: Karat (k) of Palladium Gold :: Silver Content Alloy

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.

Palladium-Gold White Gold Alloy Favourable Characteristics

Mechanical characteristics are widely divergent due to their palladium content. Palladium-based white gold alloys have the following favourable characteristics:

• Palladium-based alloys are excellent corrosion-resistant compounds.
• They have a very good white colour, and it is the only commercially available nickel-free white gold alloy that has a good colour.
• Palladium-gold alloys can be cast using traditional methods.
• They are inert and they are highly resistant to chemical agents.
• During melting they have no appreciable tendency to form insoluble oxides.
• Palladium-gold alloys have a low hardness. This makes them very suitable for gem setting and hand working.

Palladium based gold alloys also have the following less than favourable characteristics:

• Palladium is costly, being a traded precious metal with a daily quote.
• It has a high specific gravity, which means that the weight of the finished product is heavier and since the cost of the product is based on weight, has a consequent much higher price.
• Palladium-gold alloy is more susceptible to reaction with reaction inclusions such as calcium sulphate bonded,
• The alloys have a lesser acceptance of higher wt% of zinc.

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.

In 18 ct white gold:

• 10wt% to 13wt% of palladium is required to give a good white colour that does not require rhodium plating.
  See Rhodium Plating :: Rhodium Plate by Humagaia.
• 6wt% palladium is sufficient to give a white colour that is close the boundary with yellow .

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.

The lower karatage alloys of palladium used are:

• 14k palladium white gold alloy at a concentration from 6wt% to 14wt%.
• For 8k, 9k and 10k white gold alloys, the nickel-free and palladium-free alloys, as are commercially available, can be utilised both for lost-wax casting and for mechanical working.

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.

In 18 ct white gold:

• 10wt% to 13wt% of palladium is required to give a good white colour that does not require rhodium plating.
  See Rhodium Plating :: Rhodium Plate by Humagaia.
• 6wt% palladium is sufficient to give a white colour that is close the boundary with yellow .

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.

The lower karatage alloys of palladium used are:

• 14k palladium white gold alloy at a concentration from 6wt% to 14wt%.
• For 8k, 9k and 10k white gold alloys, the nickel-free and palladium-free alloys, as are commercially available, can be utilised both for lost-wax casting and for mechanical working.

Palladium-gold alloys have the following further characteristics with the addition of other metals:

• At high concentration the palladium-gold alloy is susceptibility to tarnishing.
• The white gold alloy, in itself, is very costly.
• The alloy has a high melting point.
• They can be allergen,
• They are ferromagnetic
• The palladium based gold alloy has an increased melting temperature.
• In high proportions palladium produces high hardness and poor workability.
• High proportions of zinc can cause problems within the refinery recycling industry.
• These higher proportions cause poor workability very rapidly as the percentages increase.
• They are toxic. 
• Palladium gold alloys cause poor cold workability.
• They also show high reactivity which can cause application difficulties.
• Palladium has a low solubility in gold which increases the probability of corrosion.
• In proportions above 10wt%, iron causes excessive hardness, poor cold working and the possibility of oxidation during investment casting.
• There is a tendency towards high reactivity and to oxide formation.
• Manganese proportions above 10wt% instigates high reactivity which can cause application difficulties. This problem is reduced if manganese is used in conjunction with palladium.

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. Palladium is included for the following reasons:

• Palladium decreases the hardness of the casting. This makes it particularly suitable for gem setting in the main.
• Palladium decreases the ate of nickel release.
• Palladium brightens the white colouration whilst having little effect on the hardness.
• Palladium increases the resistance to corrosion.

Some palladium-based white golds also contain small additions of nickel at the rate of 1wt% to 2wt%. In low karatage alloys it is common for 8k to10k, silver-containing alloys, where nickel absence is less important than mechanical characteristics and compliance with the European Directive on nickel.
See Nickel Allergy :: White Gold by Humagaia.

The reasons for nickel additions are as follows:

• Improved ductility and malleability,
• Increased hardness,
• Increased resistance to corrosion and to sulphur attack,
• Decreased grain size in white gold alloys.

Palladium-based white gold alloys with low nickel content comply with EU directive on nickel release, but cannot be defined as nickel-free..

The following metallic elements have limited solid solubility:

• Cobalt (Co)
• Chromium (Cr)
• Iron (Fe).

The following metallic elements have limited solid solubility and formation of intermediate phases:

• Indium (In)
• Aluminium (Al) Aluminum
• Niobium (Nb)
• Tin (Sn)
• Manganese (Mn)
• Tantalum (Ta)
• Zinc (Zn)
• Titanium (Ti)
• Vanadium (V).

Platinum and palladium are unattractive because of their high cost. 

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

• Indium, nickel and tin effect best bleaching.
• Tin, chromium, indium and zinc are very effective bleachers at relatively low concentrations
• Aluminium, manganese and titanium react with air and are rapidly oxidised.
• Niobium, tantalum and vanadium tend to increase melting point too much.
• Silver and cobalt are moderately effective bleachers and form gold alloys that are soft and workable.
• Iron and indium increase the liquidus temperature of white gold.

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