From Rough to Finished Gem
While considering an interesting Gem Topic of the Month subject , I decided that a basic introduction to the faceting process might be in order. I think there are many gem enthusiasts interested in learning how to facet gems but they might feel a bit intimidated by the process. Please remember that this article describes how I go about faceting a stone and not how I think others should facet. There are many, many ways to approach faceting.
The first step of the gem cutting process is the selection of uncut stones, or facet rough. The most important factor for selecting rough is color. If a stone is too dark or has a color that most people dislike, all the faceting skills in the world will not produce a desirable gem. I had a khaki colored peridot at the store priced at $0.00 and it took 3 years before a high school student finally took it away. Next, the faceter tries to select rough that is free of inclusions, and this can be tricky. When examining a stone, I usually dip it in a commercial refractory fluid or clove oil, which makes it easier to see what is inside the stone. I then use a penlight to illuminate the stone FROM THE SIDE so the light can reflect off the inclusions. At gem shows I can't use the refractory fluid, so I prefer to examine rough at home. If a piece of rough has a rind, or rough surface, on it, you cannot sand a 'window' to look at the interior. If you alter the rough in any way, you've bought it. The next factor to be evaluated is the shape of the rough. If you are wanting to cut a round, square, wide oval or a wide rectangle, selecting a narrow, peanut shaped stone will result in a lot of waste. In general, long, narrow stones are the least desirable and usually a rough like this must be sawn so that two or more smaller stones can be cut from it. The only time I will buy a rough like this is if I need to cut a matched pair.
The photo below shows a typical selection offered by a first-class online facet rough dealer. When a new list comes up, buyers are competing with each other and must do their evaluations and selections quickly. This is exciting and fun, and although I wouldn't exactly call this a form of gambling, I never feel the need to visit one of the local casinos.
So, now you have your piece of rough. First, you must examine the rough as described above to decide if you want to keep it. You might also want to evaluate the stone's reaction to different types of light. The two photos below were taken using standard incandescent lighting and Reveal lighting. As you can see, natural colored gems are almost always going to show color variations depending on the light source.
Now that you've accepted and paid for your rough, you are free to window it. While examining this garnet, I saw a reflection coming from an inclusion. It shows up as a white dot in the center of the stone in this picture.
To help locate the exact location of this inclusion, it will be necessary to window the stone.
The inclusion is now visible just left of center. What looks like an inclusion above it is actually a surface pit on the bottom of the stone. This inclusion will have to be taken into consideration in the planning and cutting of the stone. There is no way to cut it out of the stone during faceting and it is crucial that it is not broken into during faceting. People do not appreciate having holes in their gems.
Now it's planning and setup time and I take out my templates. After buying every template on the planet, I now use templates with lines at 90 degrees, 180 degrees, etc. .
After laying the various shaped holes over the stone, I've decided that this stone is best suited for a round. I will now lay the appropriate sized template hole on the temporary table and make four marks corresponding to the template lines on that table.
I then extend the lines down the sides of the rough.
I then make four lines on the sides of the brass dop that the stone will be attached to and the stone is ready to dop.
Dopping is a process I could write about ad nauseum, but basically, using an alcohol lamp, I heat the brass dop and apply melted dop wax to the end of the dop. Then I gradually heat the stone and apply wax to the temporary table while holding the stone in a surgical clamp. I then position the stone on the dop and release the clamp. Using my fingers, I line up the marks on the dop with the marks on the stone, using the pain in my fingers as a guide to whether the stone is still warm enough to assure me that enough heat was used for a good bond. When the stone and dop cool off after about 3 or 4 minutes, I pick up the dop and try to pull the stone off. If a stone is going to come off the dop, this is when you want it to happen. Now the stone is ready for cutting.
Needless to say, safety is a concern with my dopping procedure because I use wax rather than shellac or epoxy. I use a drilled out Lincoln log to hold the dop. Do NOT try to hold it in your fingers. DoNOT wear shorts while dopping. Do NOT use denatured alcohol as an aftershave, light your alcohol lamp right away, bend over said lamp and set your mustache on fire. Well, that's enough about dopping. There are many dopping techniques--too many to cover here.
The garnet is now ready to cut. It is placed in the facet-head spindle and secured.
With the facet-head protractor set at 90 degrees 16 girdle facets are ground with the quill set at the unnumbered lines(1,3,5,7,9,11,etc) using a 100 grit diamond plate, or lap.
The girdle facets should be the same width.
Now the protractor is set at the desired pavilion main angle and the mast and facet-head are moved closer to the grinding plate. It is important to position the mast so that the stone can reach the entire surface of the plate. This will make it so the plate will wear evenly. Eight pavilion main facets are now ground to almost a point with the quill set at 4, 8, 12, 16, etc.
A very fine plate is then used to bring the pavilion mains all the way to a point at the culet.
As you can see, our little inclusion is well out of harm's way. After the girdle is reground on a finer lap, it's time to put in the pavilion-girdle facets. The protractor is set at about 2 degress higher than the angle that was used for the mains. If you used 41.5 degrees for the mains, you'll use 43.5 degrees for the pavilion girdle facets. The facets will be ground with the quill set on the same unnumbered lines that were used for the girdle facets. How this was going to work really had me confused when I cut my first stone. After I cut my first facet I thought I'd ruined the stone because this facet extended over the dividing line between the two mains. When I cut the next facet on the following unnumbered line, it all came back to the right place to match what I had seen on the cutting diagram.
I was greatly relieved and completed the rest of the pavilion girdle facets.
It is now time to polish the facets. For garnet, I use a Corian polishing lap with Linde A polishing compound. Linde A is an extremely fine corundum powder that I mix with vinegar to make a thin film on the surface of the lap. The facets are polished on the same numbers and at the same angles at which they were ground. I get the best results if the polishing lap is spinning at a slow speed. If all goes well, polishing is fun. You will notice in the photo below that you can see our little friend, the bubble-like inclusion, again.
So--how do you know when a facet is polished? When I can no longer see any pits or scratches, I figure a facet is polished, BUT I give each facet 7-10 more seconds on the lap just in case. It just doesn't take that much more effort. When I first started cutting, I didn't think the polish on the pavilion facets was important. I was very, very wrong! A stone will look dirty and lifeless if the pavilion facets aren't polished correctly.
After a final inspection, the stone is ready to be transferred to a cone dop so that the crown can be cut.
In order to do this, a transfer fixture is used. Both dops are placed in the fixture.
The cone dop is heated over the alcohol flame and heated wax is dripped into the cone dop. You do NOT heat the stone or the dop holding the stone. While the end of the cone dop is held over the flame, the pavilion of the stone is firmly pushed into the hot wax.
After allowing the wax to cool, both dops are removed from the fixture and at this time they are both stuck to the stone. I then try to pull the dops apart to make sure the stone is firmly in place is the cone dop. If it is, I then heat the original flat dop to release the stone from it.
Realigning the stone so that the crown facets line up with the girdle facets is simple when you have a faceted girdle. The appropriate girdle facet is placed on a T-angle plate which is on a lap and the stone is locked into place.
Now the crown is ready to be cut. The first step of faceting the crown is the grinding of the 8 crown mains using 4-8-12-16 etc. Since this is a garnet, I will set the protractor at 38 degrees. If this were a tourmaline, I would use a different crown angle. Like the angles used for pavilions, there are variations based on the optical properties of the stones being cut.
Then 16 crown-girdle facets are cut at 45 degrees using the unnumbered lines(1,3,5,7,9,etc). If crown-girdle facets that extend farther toward the table(top of the stone) are desired, the angle can be lowered a bit and 44.6 degrees can be used.
After the 16 crown-girdle facets are finished, the crown-table, or star facets are cut. The protractor is set at approximately 15 degrees lower than the crown mains(38-15=23 degrees) and the star facets are cut at index numbers 2,6,10,14,18 etc. Notice that in the picture of the index wheel that these numbers are right between the numbers the mains were cut on. These facets will come down to where the points of the crown-girdle facets meet.
I didn't think this meetpoint was important until I found out that professional cut evaluators like Robert James of the ISG look at these very closely. There is a reason for that. If facets are left like you see them in the photo above, light is deflected away and kept from entering and exiting the stone. It is also a good indicator of how much care was taken during the faceting of the stone. When these facets are finished, the crown facets are ready to be polished.
Not wishing to make readers sit through another polishing session, I decided that it was time to move on to the cutting of the table facet. In order to cut the table facet, the stone is removed from the facet-head. Then a 90 degree block is positioned in the head and the dop is inserted in the block and locked into place.
The table facet is then cut down to the tops of the kite shaped main facets.
You can see in the photo that the table facet is not quite there yet. I usually bring it in on the 3000 grit lap until it is just short of the tops of the mains. I usually cut the table facet a tiny bit short of the mains so that if the table gets scratched during setting, the stone can be repaired without the entire crown having to be recut.
The dop is left in the 45 degree block for the final polishing of the table. Polishing the table can take persistance and I use a 10x loupe attached to a pair of reading glasses and a small LED gooseneck light to inspect the table instead of the #10 Optivisor I use for the rest of the stone. When the table is polished, the stone is removed from the dop using the alcohol lamp and after the stone cools, the wax is removed from the stone using denatured alcohol. The stone is then cleaned with window cleaner and it's time to see what's been created.
The picture on the left shows the stone under Reveal lighting and the one on the right shows what it looks like under standard incandescent lighting.
When faceting procedures are written out, it always makes it seem like each step takes a long time when it really doesn't. The crucial setup procedure takes about 15 minutes and the transfer step takes about 5. I hope this article has adequately explained the basic steps of faceting and will encourage gem enthusiasts to seriously consider creating their own gemstones.