These two components are almost always built as one unit to ensure that there is no uncertainty in the angle at which the stone strikes the lap. This motor drive must provide spin that is perfectly horizontal, or flat, relative to the assembly which holds the gem. Inconsistencies and inaccuracies of less than a degree can destroy the precision of a custom cut gemstone.

So, you have a fixture to hold the gem exactly where you want it, and you have a precisely-mounted motor and drive to turn the laps needed for cutting. Other than that, you just have the gem cutter and his gem.

In Part 2, we talked about the choice of faceting designs and the impact that choice would ultimately have on the finished gem. Well, now we take that facet design and put it into practice, executing it on the stone we've chosen. Gems are actually "cut" multiple times: at least once to remove a significant amount of material and establish the facet meetpoints, and once to polish those same facets. In affect, the gem cutter is cutting the same design twice (at least). Usually, a stone must undergo a rough cutting, a finer cutting (called a prepolish) and finally a polishing step.

The first step, as mentioned above, is a rough cutting to rapidly remove a large amount of material. If you'll think back to Part 3, you'll recall that a lap is covered with many tiny diamonds, which work to grind away the gemstone. There are