The idea of the 4C’s dates back to the mid 20th century when the GIA (Gemmological Institute of America) tried to find a way to evaluate diamonds. They found that the four criteria determining the value of a diamond were: carat, color, clarity and cut. The same parameters can also be used to evaluate a colored gemstone.
The carat measures the weight of the gemstone. One carat is equal to 0,2 g ( 200 mg). As a rule the larger a gemstone is the higher is its price per carat.
Colored gemstones come in a multitude of different colors, hues and intensity of color. Some crystals will also display an array of different tones depending on the angle by which they are viewed ( ie. Green Tourmaline, Tanzanite, Sphene). Some gemstones even show different colors according to the axes of the crystal (dichroism or pleochroism).
Internal defects of gemstones are commonly called inclusions. These imperfections may result from gas, bubbles, cracks, scratches or the inclusion of foreign crystals. These inclusions can affect the gemstone’s ability to properly transmit light and may therefore be detrimental to its beauty.
An accurately cut and facetted gemstone will reflect most of the light back at the viewer through the top of the stone causing what we call brilliance. It is most important that facets are positioned in such angles that the gemstone will display is highest possible brilliance. To assure the look of a perfectly cut gem the facets must be located in a symmetrical way and pleasing pattern.