Pure gold is a deep yellow color and conventional carat gold Jewelry alloys can range from red through yellow to pale yellow/green and even white by varying the alloying metals.
April 21, 2006 (Press Release) --
But gold is yellow?
Pure gold is a deep yellow color and conventional carat gold Jewelry alloys can range from red through yellow to pale yellow/green and even white by varying the alloying metals. But it is possible to make gold Jewelry that exhibits unusual colors such as purple and blue and black. How is this possible? Well, this can be accomplished by one of two techniques: formation of special gold metal compounds (intermetallic compounds) or by a surface coating or patination. Both approaches can yield attractive colors but they do have some disadvantages over normal carat gold alloys.
Blue gold
The intermetallic compound formed between gold and indium, AuIn2, gives rise to a clear blue color and that between gold and gallium, AuGa2, to a bluish hue.
AuIn2 (46% gold) and AuGa2 (58.5% gold) have melting points of 540.7°C and 491.3°C respectively. Off-stoichiometric compositions, like purple gold, will be 2 phase and so can be expected to have some measure of workability and toughness. Manufacturing techniques will also be similar to those for purple gold.
A blue patina can be produced on gold alloys by oxidation treatments. In one case a 20 -23 carat gold alloy that turns to a rich sapphire blue is alloyed with ruthenium, rhodium and 3 other metals. It yields a blue surface layer 3 -6 mm thick. In another case an18 ct gold with 24.4% iron and 0.6% maximum nickel forms a blue oxide layer when heated at 450- 600°C. At a higher, 83% gold content, a blue-green color is produced.
Oxidation of gold alloys containing 25% iron or arsenic is also reported in the literature to yield a bluish color.
Note - Many of these coatings will be vulnerable to rubbing or abrasion and so should be protected
where possible.
Source: http://search.msn.com
Pure gold is a deep yellow color and conventional carat gold Jewelry alloys can range from red through yellow to pale yellow/green and even white by varying the alloying metals. But it is possible to make gold Jewelry that exhibits unusual colors such as purple and blue and black. How is this possible? Well, this can be accomplished by one of two techniques: formation of special gold metal compounds (intermetallic compounds) or by a surface coating or patination. Both approaches can yield attractive colors but they do have some disadvantages over normal carat gold alloys.
Blue gold
The intermetallic compound formed between gold and indium, AuIn2, gives rise to a clear blue color and that between gold and gallium, AuGa2, to a bluish hue.
AuIn2 (46% gold) and AuGa2 (58.5% gold) have melting points of 540.7°C and 491.3°C respectively. Off-stoichiometric compositions, like purple gold, will be 2 phase and so can be expected to have some measure of workability and toughness. Manufacturing techniques will also be similar to those for purple gold.
A blue patina can be produced on gold alloys by oxidation treatments. In one case a 20 -23 carat gold alloy that turns to a rich sapphire blue is alloyed with ruthenium, rhodium and 3 other metals. It yields a blue surface layer 3 -6 mm thick. In another case an18 ct gold with 24.4% iron and 0.6% maximum nickel forms a blue oxide layer when heated at 450- 600°C. At a higher, 83% gold content, a blue-green color is produced.
Oxidation of gold alloys containing 25% iron or arsenic is also reported in the literature to yield a bluish color.
Note - Many of these coatings will be vulnerable to rubbing or abrasion and so should be protected
where possible.
Source: http://search.msn.com
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