You all know the 4 c's right? Well, 3 of those c's have to do with the "fire". Color, cut, and clarity. The cut is the single most important factor in turning gem-quality rough into a stone of value and quality. This is why the best diamonds , ie the ones with most "fire' come from the Israeli cutting houses. The precision that goes into faceting a stone would make the precision machining industry quite jealous. You can also do a precision facet on a poor quality diamond or a bort, and you won't get any fire at all.