Because of the softness of pure (24k) gold, it is usually alloyed with base metals
for use in jewelry, altering its hardness and ductility, melting point, color and
other properties. Alloys with lower cartage, typically 22k, 18k, 14k or 10k, contain
higher percentages of copper, or other base metals or silver or palladium in the
alloy. Copper is the most commonly used base metal, hence getting a red color.