Pure (or Fine or 24 carat) gold has a lovely warm rich yellow color that is highly prized. It is actually an orange shade of yellow. Unlike other precious metals, gold Jewelry can be produced in various alloys of gold, known as the carat/karat gold's, in a range of colors from white to yellow and through to red. In addition, it is possible to achieve other special colors such as blue, black and purple. So how is it possible to change the intrinsic color of gold? [An alloy is just a mixture of two or more metals; e.g. brass is an alloy of copper and zinc.]

The simple answer is that it is like an artist mixing his paints to obtain various hues. Every schoolboy (and girl) knows that mixing yellow and blue produces green and mixing yellow and red produces pink or rose. With metals, we only have the choice of mixing yellow (gold) with red (copper) or white/grey (all other pure metals). So for the carat gold's, we can maintain yellow at the medium and low carats by balancing the amount of copper and silver plus zinc alloyed into the gold. If we add more copper than silver, then we get redder shades and adding more silver or other metals than copper gives us paler colors and even white.

However, we should note that, for a given carats of gold, varying the color also changes other properties, such as hardness and strength. We should also note that we can obtain a wider variation in color as we lower the carats. This is all explained in more detail in the section on gold jewelry alloys. White gold's, in practice, are a little more complex since the whitening - or bleaching - effect of different metals on gold varies: see the section on white gold's.

The special colors such as blue, black and purple are obtained by quite different approaches, either as special metal compounds or by surface treatments to obtain a patina. This is explained in the section on special colors.

Source: http://www.jewelrybynet.com


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