affect the colour, malleability, and melting temperature of gold

Gold and silver bars copper, silver and gold - usually lies dormant in the immediate vicinity deep down in the earth's crust and are also often brought together to produce gold alloys. Gold alloys are melted gold to which other metals are also added in the melt. The reason for this is:

In order for gold to be processed as easily as possible for jewellery production, the precious metal must have certain properties. The addition of zinc, tin or cadmium, for example, reduces the melting temperature and surface tension of gold, which means less energy is required for melting and allows improved formability. 

Another advantage of adding other metals to the gold melt: Gold itself is a very "soft" metal. Unsightly scratches would easily appear on the surface of a piece of jewellery made of pure gold. However, the addition of platinum or nickel increases the hardness of gold. However, any admixture of other metals also reduces the special properties and qualities of gold: the colour changes, the density decreases and the precious metal also decrease in value. A lot of sensitivity is required from the goldsmith to achieve the best possible result with an alloy.

The difference between the numerical and mass fraction of gold in gold alloys

The changes in the gold properties achieved by adding other metals to liquid gold are always the result of a changed atomic composition. More specifically, the number ratio of pure gold atoms to the total number of atoms in an alloy change. The ratio by weight must always be distinguished from the pure numerical ratio. Gold has an atomic mass number of 197, while copper, for example, only has 63 (about a third less weight). This means that with an atomic number ratio of 1:1 (same number of gold and copper atoms) gold has a much higher mass fraction - namely from 756 parts to 1000, i.e. about 75% mass fraction. In fact, however, it has a numerical share of only 50% in the alloy. On the one hand, the value 333 on a gold alloy indicates that the alloy consists of one-third of the weight of gold. On the other hand, however, the proportion of gold atoms in relation to the other metals is well below one third. A low number of gold atoms is in turn at the expense of the material properties. 333 gold alloys generally tarnish very quickly, are not corrosion resistant, and do not have a convincing colour. For this reason, these alloys are no longer officially referred to as gold.

Gold alloys fascinate with their versatile colour spectrum

The colour effect of a piece of jewellery made of gold is one of the most important beauty criteria for the viewer when buying it. Gold alloys allow a wide variety of colourings. Some metal additives impair the colour, while others give the alloy a special shine or create other fine optical nuances. 

While the hard 585 gold alloys shimmer rather pale, softer alloys with at least 75% gold by mass impress with their intense shine. 

The goldsmith selects the alloy primarily based on the technique he wants to use to process the gold and how the finished piece of jewellery should ultimately look. In order to achieve an attractive colour effect, copper, silver, palladium or nickel is added in a specific mixing ratio. 

These metals bring their very special colour tones into the alloy, which in the respective combination leads to very individual, interesting colour spectra: starting with a shimmering copper-coloured red gold and a more silvery yellow gold to green, grey or white gold. 

There are several alternatives for producing a white gold alloy. To give gold jewellery that special white sheen, it is "rhodium-plated", which means it is additionally coated with a layer of rhodium. On the one hand, the rhodium coating creates a special, white shine and, on the other hand, also makes the surface of the jewellery significantly harder.

Gold-Titanium Alloys - the gold from which wedding rings are made

A special case is a gold-titanium alloy. It is mainly used for the production of wedding rings or in medical technology. The almost pure gold is refined with one per cent titanium. The alloy is extremely strong and shimmers almost as yellow as 750 gold. The added titanium only allows a fine, subtle shade of grey to flow into the alloy.