4 - Cut and Value Flashcards
Proportion
The angles and relative measurements of a polished gem, and their relationships to each other.
Finish
The quality of the polish and the precision of the cut (symmetry.)
Make
The qualities of a faceted diamond’s proportions and finish.
Brilliance
Light reflected off the surface of a diamond.
Refraction
The change in speed and possible change in direction of light as it travels from one transparent material to another.
How does refraction occur in a diamond?
Refraction occurs when light enters a diamond, slows down, travels at a different angle, and strikes the interior surface.
Once light has struck an interior surface of a diamond, where does it go?
It either continues to reflect or exits the diamond.
Refractive Index (RI)
A measure of the change in the speed and angle of light as it passes from one material to another.
Dispersion
The separation of white light into its spectral hues.
What is fire the result of?
Dispersion
Scintillation
The flashes of white and spectral-colored light as the light, observer, or diamond moves.
What are the objectives of a planner and what do they look at?
A planner has to maximize carat weight and determines this yield by inspecting structure and interior features.
Blocking stage
When a diamond gets its first 17-18 facets and establishes initial symmetry.
What proportion measurement is checked during cutting?
Pavilion angle
Brillianteer
Someone who polishes the final facets on the diamond.
When does the girdle become polished or finished?
It is one of the last steps in the polishing process.
Girdle outline
A diamond’s face-up shape.
What kind of shape is more dependent on girdle outline?
Fancy.
Shoulder
One of the two sides adjacent to the rounded end of a pear or oval shape.
Wing
One of the two sides near the point of a marquise, pear, or heart.
Table size
Table size expressed as a percentage of the average girdle diameter.
For round brilliants.
Average girdle diameter (AGD)
The result achieved by averaging the smallest and largest girdle measurements of a round brilliant.
What basic measurement is used in many proportion calculations?
Average girdle diameter.
Crown angle
The angle formed by the bezel facets and the girdle plane.
At what crown angle do diamonds become more susceptible to damage?
Shallower than 25 degrees.
How is girdle thickness judged?
By eye.
What are the visual consequences of a thick girdle?
Large, fuzzy, grey reflections. May make stone appear dark. Occasionally enhances a fancy-colored diamond.
Where should girdle thickness vary in a round, oval, or cushion brilliant?
The thickness should be thinner between pairs of mains and half facets, and thicker where the points of the crown and pavilion main facets meet.
Why is it good to vary the girdle thickness?
It can prevent chipping at points.
How should an unpolished girdle appear? How should it not appear?
Should be frosty and waxy, faceted, or polished. It should not be rough and granular.
Pavilion depth
The distance from the bottom of the girdle plane to the culet, expressed as a percentage of the AGD.
To what light features is pavilion depth critical?
Brightness and fire.
Fisheye
When the girdle reflection forms an unattractive gray ring and gives a dull, flat look.
When does a fisheye occur?
When the pavilion depth <38%, or has a normal 40% depth with a large table.
At what pavilion depth will a gem usually look dark in center?
Deeper than 49%.
Nailhead
A dark area under the entire table.
What is a nailhead caused by?
A pavilion depth of 50% or more.
Pavilion angle
The angle formed by the pavilion main facets and the girdle plane.
Dark bow-tie
Appears as described under table.
How can a dark bow-tie be mitigated?
Can balance light display with an elongated culet or with changing the pavilion angle.
Pavilion bulge
Larger-than-usual pavilion angle on the middle tier of facets designed to add weight to a step cut stone.
What are the difficulties of a pavilion bulge?
Can reduce brilliance, become more difficult to set.
Total depth
Table-to-culet depth, expressed as a percentage of AGD. Combines crown height, girdle thickness, and pavilion depth.
What does a total depth of <55% indicate?
Shallow crown or pavilion.
What does a total depth of >65% indicate?
Crown or pavilion might be deep and the girdle is probably thick.
How is culet size determined?
It is visually inspected.
What is the purpose of the culet?
To protect the bottom of the gem against accidental chipping.
How can one see a medium culet?
Under 10x, not with the naked eye.
How can one see a large culet?
With the naked eye, easy to spot without magnification.
Length-to-width
Ratio of a fancy shaped diamond.
What is the typical L:W ratio of a marquise?
1.75:1 - 2.25:1
What is the typical L:W ratio of an oval?
1.33:1 - 1.66:1
What is the typical L:W ratio of an emerald cut, rectangular cushion, or pear?
1.5:1 - 1.75:1
What is the typical L:W ratio of a heart?
1:1
What is the ideal table size of a round brilliant?
50-66%
What is the ideal crown angle of a round brilliant?
25-35 degrees
What is the ideal pavilion depth of a round brilliant?
42-44%
What characterizes the pavilion depth of a small stone?
Usually deep.
In what case would a cut gem carry up to 10% of its weight in its girdle?
In the case of a small stone, where shape is not as much of a concern.
What is the ideal table size of an emerald cut?
> 70%
What is the ideal pavilion depth of a fancy shape?
50% or more
How are proportions useful to an appraiser?
They can yield accurate weight measurements with the correct tools and formulas.
Polish
The overall condition of the facet surfaces of a finished diamond.
What are the polish grades?
Excellent, Very Good, Good, Fair, Poor
What does an “excellent” polish grade mean?
“Superior” with very few hard-to-find blemishes.
What does a “very good” polish grade mean?
Faint polish lines or inconspicuous minor polish features.
What does a “good” polish grade mean?
Noticeable white polish features.
What does a “fair” polish grade mean?
Obvious polish features.
What does a “poor” polish grade mean?
Obvious polish features that reduce overall transparency.
Symmetry
The exactness of a finished gem’s shape and the placement of facets.
List 8 common symmetry variations.
Table or culet off-center
Girdle outline out-of-round
Facets that fail to point properly
Misaligned crown and pavilion facets
Table is not a regular octagon
Misshapen facets
Extra facets
Uneven outline
What are the grades for symmetry?
Excellent, Very Good, Good, Fair, Poor
What goes into a cut grade?
Polish, symmetry, proportion, and light features.
Light features (personal)
Brilliance, fire, fluorescence, transparency, and scintillation.
Design
A diamond’s physical shape, including its proportion and durability, determined by decisions made in the fashioning process.
Craftsmanship
The care that goes into the fashioning of a polished diamond, as confirmed by its finish.
What cut has excellent light features?
Round brilliant or triangular brilliant.
What is a selling point of an oval diamond?
They often look larger than round diamonds of the same carat weight.
What are some selling points of a marquise?
Can compliment long fingers and can appear larger than round diamonds of the same carat weight.
When would you recommend a princess cut?
As an alternative to emerald cut to those who like brilliant cuts.
What qualities would you emphasize with an emerald cut?
Elegance, and transparency.
