How to Cut and Polish a Star Sapphire or Star Ruby

After choosing your best piece of Sapphire or Ruby crystal,( Corundum) follow these steps for best results.

Place your crystal on the saw table of your encabachon cutting machine. The author uses a Graves Cabmate but steps are the same on any machine.
Make sure crystal is on its flattest most level face, if needed build crystal up with softened dop wax until it is perfectly flat &level with the C axis of the crystal parallel to the saw blade. Make sure there is a plentiful supply of coolant flowing at the point of cut and that you have plenty of light.
Feed crystal evenly into diamond saw blade to get an even cut and to keep blade from crimping Cut a slab off of the crystal approximately 1/4 of an inch thick.

Light reflecting off of rutile inclusions within the crystal at a 60 degree angle creates the "star" when these reflections are sharp & crisp you get a star when they are defuse you get a moon. The star is more desirable and therefor the more valuable.

Place your slab with the most appealing view upward. Using a template and aluminum pencil put the "Flash of Light" (Chatoyency) in the center of the slab & mark dimensions of desired shape. Shapes are usually Round,Oval, Square, or free form. Free form keeps the natural shape of the original 6 sided crystal.
In order to "center" the flash of light in the slab it may be required to build up one or the other side of the slab with dop wax as we did with the crystal.

Next we put our rough diamond wheel & table on the machine. This wheel is usually a 80 to 100 grit. Next place your coolant flow on the wheel face and move your slab around on the wheel with your fingers until the outer shape you marked with the aluminum pencil is roughed in.

Next dry off your slab using an alcohol lamp. Then using green or black dop wax attach stone to a piece of dowel rod sufficient in diameter to support stone (about like a pencil or slightly larger) Stick should be 6 to 8 inches long. Support the end of your dopstick with the stone on it between two finger resting on cutting table use other hand to hold end of stick & rough in a dome shape. Once you have the dome cut change wheels to a 120 grit & start removing the grinding marks while refining the shape.Use progressively finer grit wheels until you get to 600 grit. Always keep a coolant flow on wheel.

Once you have finished removing grinding marks & refining shape on the 600 grit wheel you will be moving onto Diamond belts with a rubber wheel.
At this point you can put your dopstick with the stone on it into a variable speed reversible drill. The diamond belts will range as follows:

1200 grit,1800 grit,3000 grit, 8000 grit, 14,000 grit, 50,000 grit100,000 grit. Turn the drill on and allow the stone to rotate against the wheel. Keep coolant flowing.
Using the drill against the turning belt allows the stone to move in 2 directions at one time, this does a better job of removing the grinding marks & gives a higher polish to the finished gem. Once you have worked your way through the final belt put your rough cutting wheel back on.

Then take your stone off its dopstick and put it back on upside down so that the sharp edge is up and the dome is in wax. While supporting stone between two finger as before put the sharp edge of stone against wheel at a 45 degree angle cut sharp edge off. This will prepare the stone to be mounted as it creates a "girdle for the prongs to bend around. Now remove stone from dopstick clean off excess wax with denatured alcohol and enjoy your creation.