Think of a gem material as a particular and perfect combination of atoms. To determine clarity, the specimen was tightly encircled by the thumb and fore-finger, then held up to the Sun, and viewed from behind with the light passing through the material. If the material was opaque or semi-translucent, it was considered to be completely flawed. If the material was translucent to transparent, then flaws were taken into consideration to determine identity, quality and value. Such gems are ugly and inauspicious.
Fine diamonds are free of flaws visible to the naked eye.
All these grades are impossible for any ordinary person to discern using the naked eye in natural light, as they are all free of eye-visible defects. Still, through extensive advertising and promotion, even the basic diamond buyer knows that there is a huge price difference depending on clarity. Like a so-called ruby that is dense, and no better than a brick. The fact is that clean diamonds are hoarded, and then slowly sold to the public at a greatly increased value, thus creating an artificial rarity. This will then bring the clean diamond price index in line with clean colored gems.