This requires the stone to have enough depth to form the pavilion facets as well as the table facets above the girdle.
Faceting is done on a faceting machine Some special terms:
Index of refraction (RI)= Velocity of light in air/Velocity of light in substance
Diamond RI=2.42 186,300/77,000
Corundum RI=1.76-1.77
Emerald RI=1.57-1.58
Quartz RI=1.54-1.55
Main angles for critical angle, crown, Pavilion
Diamond------- 24, 35, 41
Corundum----- 35, 37, 42
Emerald-------- 39, 42, 43
Quartz----------40, 42, 43
Clean Brazilian Quartz is a good practice material.
Most faceting books have the cutting angles for Quartz as the main instruction.
A 1.54 RI, and expect the faceter to adjust for other materials.
I recommend the book:
Introduction to Meetpoint Faceting by Robert H Long, and Norman W. Steele.
The information below is to familiarize you with the concepts of faceting, Not to be exact instructions.
Any use is at your own risk.
A Diamond at 2.42 RI needs less depth on the Pavilion, in relation to the diameter than Quartz or Emerald.
This needs to be taken into consideration when deciding how big a gem you can cut from a specific piece of rough gemstone.
For instance the ratio of diameter/total depth for Quartz on a Round Brilliant is 100/69 With the Pavilion at 47% the girdle at 2% and the Crown at 20%
Terminology:
A wedding ring solitaire is usually a
click to enlarge
Round Brilliant Cut.
Facet is the plane of a cut
Table (4) = the flat top facet
Star facets (3)are the next down from the table and are equalateral triangles
Mains (2) are a shield shape with a point touching the table, and the opposite point touching the girdle.
Breaks (1) are the right angle facets resting on the girdle.
The Pavilion, is the bottom portion which comes to a point on a round brilliant, or keel on other cuts.
Girdle facets (2) are the 90 degree thin facets separating the crown from the pavilion.
Breaks (1) again are the right angle triangles next to the girdle
Mains (3) have a point at the culet (point at the bottom), and the girdle.
Now close your eyes and name the facets of a round brilliant, try again in the morning.
Can you visualize the gemstone, and rotate it in your mind?
Faceting is not difficult, if you can follow directions and have patience you can do it.
Faceting is not a garage project, a clean environment is necessary.
The planes numbered 1-4 on the crown and 1-3 on the pavilion are called steps,
You would set those angles on the arm of your faceting machine, then rotate the bearing index to specific points in a circle.
The first process would be to rough cut near the table plane, and dop your stone.
Then set up to cut your pavilion, Break facets.
SET the angle to 45 degrees, When you set arm angles use a loupe and really be aware of the position, you have to come back to this exactly on the polish step.
Put on a 100 grit lap, and spin the bearing index, slowly lower the whole arm untill you have a cone, check to make sure the point doesn't wobble.
Next CLEAN the stone and entire machine, and put on the 600 grit lap.
I use toilet paper.
THIS IS IMPORTANT! WORK OUT A SYSTEM FOR CLEANING, KEEP LAPS IN SEALED MARKED BAGGIES.
Cut 16 Break facets to a centerpoint (critical to be centered)
Spin the bearing and see if the point wobbles.
Bearing index-----93-03-09-15-21=27-33-39-45-51-57-63-69-75-81-87
SET the angle to 90 degrees.
Cut Girdle facets at the same bearing settings as the break facets.
Bearing index-----93-03-09-15-21=27-33-39-45-51-57-63-69-75-81-87
The crown needs to be 1/2 the depth of the pavilion.
Cut the Girdle facets to a depth that allows enough room for the crown.
This step determines the diameter of your stone, so there is a toss up as to cutting to a standard size, or getting the most out of the rough, and making a custom setting.
Quartz, I'd go for a standard, Emerald I would go for most out of the rough, and build a setting special.
One other factor is inclusions, a small inclusion under a break facet would be ok.
A smaller stone with excellent clarity is more valuable than a large stone with inclusions.
Fractures are another problem and generally should be cut around completely, you don't want to spend days cutting a stone, and have it fall to pieces when you try to set it.
Cut 8 Main facets at 43 degrees.
Bearing index------96-12-24-36-48-60-72-84
As you cut these, the freshly cut facet will look like an"arrow" pointing towards the meetpoint at the girdle.
The point should just "Meet" the girdle. This is called meetpoint faceting.
NOW, Remove the lap clean it and put it in a gallon baggie marked for it.
Repeat Clean machine tecniques. Clean the stone with alcohol this time.
You finish the polishing of the pavilion BEFORE you cut the crown.
FROM HERE ON OUT! ABSOLUTE CLEANLINESS IS NECESSARY! DON'T LET YOUR WIFE VACUUM BEHIND YOU WHEN YOUR FACETING.
IF YOU HAVE TO GO EAT, COVER THE LAP WITH A PAN LID YOU GOT SPECIAL FOR THAT PURPOSE.
PUT IT ON ANYTIME YOU LEAVE THE ROOM.
IF YOU CONTAMINATE A POLISH LAP, THROW IT AWAY AND MAKE A NEW ONE OUT OF PLEXIGLASS.
IF YOUR POLISHING A FACET, AND ALL OF A SUDDEN YOU HAVE A SCRATCH THAT WASN'T THERE BEFORE, YOUR LAP IS CONTAMINATED.
POLISHING FACETS
FACET DESIGNS
CUTS
Questions and Answers