Why the gold smiths add material to the gold to make ornaments

The pure gold is not useful for doing the ornaments, the pure gold is so delicate. They add materials of silver, copper, Nickel, Zinc to bring strength to the puregold.

Reasons for adding:

Why Silver:

As the proportion of silver increases, gold changes in colour from yellow to greenish-yellow, to white.

Why Copper:

As copper content increases, the gold becomes redder in appearance.

Why Nickel:

Nickel has the effect of whitening gold.

Why Zinc:

Zinc is considered a decolorizer, and is used to convert some red golds (copper alloys) into a more yellowish tone by substitution of zinc for some of the copper and silver.