Diamond type
Diamond type is a method of scientifically classifying diamonds by the level and type of their chemical impurities. Diamonds are separated into four types: Type Ia, Type Ib, Type IIa, and Type IIb. The impurities measured are at the atomic level within the crystal lattice of carbon atoms and so, unlike inclusions, require an infrared spectrometer to detect.
Diamond cutting
Due to changes in market desirability and popularity, the value of different styles of diamond fluctuate. All diamonds can be recut into new shapes that will increase value at that time in the market and desirability. An example of this is the "marquise" cut diamond which was popular in the 1970s to 1980s. In later decades, jewelers had little success in selling this shape in comparison to other shapes like the oval or pear shape. The "marquise" can be cut into an oval diamond by any diamond cutter with a loss of 5-10% in total weight. For example, a 1.10 carat marquise shape would be a 1.00 oval cut diamond by rounding the sharp points and creating an oval which currently in the market has a much greater desirability and resale value. The same marquise shape also could become a pear shape instead by only trimming and rounding the side which will be turned into the base of the pear shape.