Without question what I receive the most questions about is the stone cutting process. Most people have no idea how stones go from a piece of rough to the finished sparkling, light filled final product so commonly seen in jewelry. Stone cutting was my "gateway drug" to jewelry design.... and is probably still my favorite part of any project. In the pictures below I have documented the faceting of a 15.02ct unheated, 100% natural aquamarine. It should come as no surprise that since I am a little spacey I forgot to take pictures of some steps.
Starting Point: The piece of rough for this post is at the far right of the middle row. The carat weight is listed below each piece of rough. A yield of 25-30% is average for a cutter focused on brilliance. Most international commercial cut stones are cut for yield which results in windowed stones (where you can see through the bottom of the stone while looking at it from the top). Windowed stones are not cut with refraction and brilliance in mind and result in less lively but heavier stones. Different stones have different refractive indexes which means that the light bends at different angles when it enters the stone from above. Optically correct stones are cut so that the light that enters from above bounces off the pavilion (bottom) facets and back out through the top towards the viewers eyes. If the light rays bounce out the side or the pavilion of the stone then color intensity and "glitter" are lost. Commercial cutters often cut overly dark rough in a windowed manner as the light passing straight through the stone makes it appear lighter and of better quality than it actually is.
The pictures below shows the faceting machine. It is essentially a protractor with one end that can be rotated 360 degrees. The rotating end comes in to contact with a spinning lap. The laps can be made of different materials with diamonds of varying coarseness.
The control panel to the left of the lap is used to adjust speed and direction of the lap's rotation. The picture below is a closeup of the mast. This is where the angle of the facet and stone rotation is adjusted.
Step 1:The stone is attached to an aluminum dop using hot wax (yes I forgot to take a picture of this step). Once the wax is set, I like to wait 24hrs, the aluminum dop is slid into the end of the protractor assembly and tightened in place. Using a angles that are optimized for this type of stone - Aquamarine has a refractive index of 1.56 - I start roughing in the facets for the pavilion of the stone. Since this is such a large stone I rough it in with a very course 180 grit lap. From the picture below you can see the chewed up look of the stone with a very clear scratch pattern. At this stage I am only looking to cut the main pavilion facets without coming to a fine point. Aquamarine is a very brittle stone and trying to cut a fine point with such a rough lap creates micro fractures in the surface material which could result in the very tip chipping off.
Step 2: Once i have removed enough material to get the basic shape and outline of the stone I take off the 180 grit lap and switch to a 260. 260 is what I would normally rough a medium sized stone in with. It takes off material quickly, but does not damage the crystalline structure of the stone as much as the 180. Using the 260 I continue cutting the pavilion facets so that they come closer to a point and are more even. The surface now shows a more even frosted look.
Step 3: Switch the 260 lap for a 600. The 600 is for anything other than quartz the last lap I cut with before polishing. In order to get a good polish on quartz, a finer 1200 grit Nubond lap must be used. Using the 600 lap I cut in the smaller facets on the pavilion and the side barion facets. The 600 is great because it can remove a fair amount of material quickly but leaves a very even finish. With each step more light is allowed to enter the stone which really starts to become evident at the 600 cut level.
Step 4: Pre-polish and polish. This used to be two separate and very time consuming steps. In the last few years combination laps have become available that allow both steps to be done at the same time. The centrifical force caused by the spinning lap ensures that the fine diamond does not contaminate the inner polishing ring (this is the lap that is visible in the top picture of the entire faceting machine). Instead of having to take a stone through two full runs of every facet with the combo laps you can pre-polish a facet, wipe the stone clean and then polish the same facet, this results in flatter more perfect facets which results in a better finished stone. For the pre-polish I use 3K grit diamond and for the polish I use chrome oxide.
The picture above shows the cullet facets polished with the remaining pavilion facets still at the 600 grit level of cutting. Throughout the polish process it is important to hold the facets up to light as reflected light is the easiest way to check for minute scratches or fogginess.
Step 5: Once the pavilion has been completely polished the dopand stone are removed from the quill and placed in a transfer jig. The transfer jig allows you to remove the dop from what will be the crown of the stone and attach a new one to the just cut pavilion without the stone coming out of allignment. This is one of the most daunting parts of the process for a new cutter as a mistake here can pretty much ruin a stone. I like to use super glue for this stage as it is a cold adhesive vs. hot wax which could cause the stone to shift. Once glued I like to let the stone sit for at least 12 hours so that the glue is thouroughly cured before applying pressure to it. To remove the waxed dop I apply heat to the metal which melts the wax before trasfering much heat into the stone.
Steps 6,7,8: The new dop is inserted into the end of the quill and the whole process is started over again.
Once the table is cut and polished the stone gets removed from the dop. If the stone is flawless then it can be subjected to either cold or heat and the varying levels of contraction/expansion between the stone and the metal of the dop will allow the stone to pop off. If the stone has inclusions/imperfections (as this stone does) then the super glue must be dissolved away, which is much slower and smellier than the other method. The picture below shows the final stone, it is very difficult to accurately capture the brilliance of a cut stone without specific lighting. The foggy areas are slight veils that are only visible from certain angles, they are actually quite beautiful when viewed up close - something to be incorporated into and considered in the final jewelry piece.
