The term .585 gold refers to the purity of the gold in question. This standard of purity is equal to 14-karat gold, which is why the terms are used interchangeably. Gold that is considered 14 karats or .585 contains 10 parts alloy blended with 24 parts gold.
When 14-karat gold has .585 or greater gold content, it is considered to be plumb. This is often stamped as 14kp or .585. This distinction is necessary because 13.5-karat gold is often labeled as 14-karat gold. Unfortunately, many consumers mistake the P for plated when it actually indicates a higher-quality piece of jewelry.