The difference between Carats and Karats?
A carat is the unit of measurement for the weight of a gemstone. In the jewelry trade, you will see abbreviations such as "TCW" (total carat weight), "CT" (carat) or sometimes CW (carat weight.) The word carat comes from the Greek keration, meaning fruit of the carob tree. In ancient times, carob seeds were used on scales as a counterweight for gemstones because the seeds were of uniform size. The average weight of a carob seed is 200 milligrams and the weight of one carat is also 200 milligrams or 0.2 grams.
It is important to know that although gems are priced according to weight, weight does not tell the whole story. A stone's actual value is a combination of carat weight, cut proportions, clarity (absence of inclusions that interfere with light refraction,) and color. For instance, an amethyst that is 12 carats is a hefty stone but is it a deep, plummy, bluish-purple? Is it cut to refract light or is there a large, flat plane when you look from the top? If that plane is too large, light will be forced to exit the stone, thus diminishing the brilliance and color purity of the stone. So, quality is not judged by carat weight alone.
We are not sure how the word karat came to define the purity of gold. It is most likely related to carat (carob) but it may indirectly have to do with weight because it is a measure of gold's purity. The purer the gold, the heavier it is.
Pure gold is too soft to submit to the wear and tear of daily life without incurring major nicks and distortions. When it is alloyed with other metals (zinc, nickel, palladium, silver, copper), gold becomes harder and more durable. "KT" is the most commonly used abbreviation for karat, although some use only "K."
Pure gold is 24KT. No alloys or additives of any kind.
22KT gold is 91.6% pure gold (22 parts) and 8.4% (2 parts) alloy.
18KT gold is 75% pure gold (18 parts) and 25% (6 parts) alloy.
14KT gold is 58% pure gold (14 parts) and 42% (10 parts) alloy.