Assignment 9 - Cut Flashcards
The angles and relative measurements of a polished gem, and the relationships between them.
Proportions
What properties of the rough determine how the stone is fashioned?
Quality: intensely colored ruby rough can produce cut stones of superb face-up color even if their proportions are less than ideal, or the finished gems are small.
Transparency: Usually, cutters only facet transparent rough. Translucent and opaque gems don’t benefit much from faceting.
Inclusions: Some gemstones have many cracks and fissures. Emeralds, for instance, are commonly fractured due to the way they form in the earth. The mining and recovery process might also cause some damage. It’s easy to remove shallow fractures, but deep fractures can limit the shape of the finished gem, and heavily fractured areas might need to be removed entirely. The rough might even split into two or more pieces, forcing the cutter to consider them separately.
Color distribution: In the most desirable rough, the color is distributed evenly throughout the stone. Unfortunately, this is very rare, and many gems have uneven color distribution. For example, sapphire and amethyst rough commonly contain strong bands of color parallel to the crystal faces. If the cutter isn’t careful, this color zoning might be visible enough to negatively affect the beauty of the finished stone.
How do a cutter’s decisions balance beauty and economics?
High end. Size > beauty.
Middle: Beauty > Size
Low end: cheap labour
What are the steps in the cutting process?
0) selecting suitable rough
1) sort the rough by size
2) cobbing to remove included material
3) sawing
4) grinding
5) preform
(wait for order)
6) faceting
7) polishing
What’s the most crucial cutting stage?
The preform stage has the greatest impact on the value of the finished gem, so it requires the attention of highly skilled workers.
Removing heavily included sections from gemstone rough by carefully tapping it with a small hammer.
Cobbing
Dividing gem rough into easily handled pieces and removing waste areas.
Sawing
Giving approximate shape to a gemstone, or producing flat planes for polishing facets.
Grinding
Top part of the gem above the girdle.
Crown
Facet at the top of the crown, usually the largest facet on the stone.
Table facet
Lower part of a faceted gem below the girdle.
Pavilion
Narrow section that forms the boundary between the crown and the pavilion, and functions as the gem’s setting edge.
Girdle
Rough ground to the approximate shape of the finished stone; also, the act of producing this
shape.
Preform
Wooden or metal stick that holds the preform during faceting.
Dopstick
Horizontal spinning metal disk used to grind or polish a gem’s facets.
Lap
Device that holds the dopstick at precise angles to allow correct orientation during faceting
and polishing.
Faceting head
Final stage in gem cutting
that produces the smoothest
possible surface.
Polishing
The arrangement of a stone’s facets.
Style
Cutting style with triangular or kite-shaped facets that radiate from the center toward the girdle.
Brilliant cut
Cutting style with mainly square and rectangular facets arranged in concentric rows.
Step cut
A cutting style that combines brilliant-cut and step-cut facets.
Mixed cut
A smoothly rounded polished gem with a domed top and a flat or curved base.
Cabochon
A gem carving style in which the design, often a woman’s profile, projects slightly from a flat or curved surface.
Cameo
A design engraved into the surface of a gemstone.
Intaglio
Artistic gem cuts that aren’t limited to specific proportions or shapes.
Designer cuts
A free-form cut that can feature alternating curved and flat surfaces.
Fantasy cut
Light that eventually returns to the eye after entering a gem through the crown, reflecting off
its pavilion facets, and exiting back through the crown.
Brilliance
How do differences in pavilion depth affect a gem’s appearance?
Flat stones with shallow pavilions usually have areas of lower color intensity, called windows.
You’ll usually see dark areas, or extinction, through the crown in stones with deep pavilions.
How do you examine a gem to judge its brilliance?
Clean the stone, then pick it up with tweezers by its girdle. Look at the stone face-up and estimate the percentage of the stone’s entire surface that returns light to your eye. Make sure you ignore any surface reflections. Also remember that even well-cut gems can show some windowing and extinction at certain viewing angles. Rock the stone back and forth, but don’t tilt it any more than 30 degrees or so.
> 75%: excellent.
60-75%: very good.
40-60: pretty good.
25-40%: there’s substantial light leakage, and this will detract from the attractiveness of the stone.
<25%: The stone has very serious proportion problems. Most of the light was lost through the pavilion facets.
Which proportion problems are the most serious?
Lack of symmetry as well as excessive depth or shallowness.
How is a stone’s symmetry judged?
When you consider the symmetry of a cut gem, you assess its shape from above—the face-up position—and from the side—the profile position.
Which three factors do you consider when assessing a gem’s finish?
- quality of the surface condition or polish
- symmetry
- number and placement of its facets
How do you put a stone’s qualities together to evaluate cut?
Overall assessment of:
- Brilliance
- Face-up symmetry
- Profile symmetry
- Ratios (length-to-width, table to pavillon)
- Bulge/girdle thickness
- finish (polish, symmetry and facets)
The precision and balance of the corresponding parts of a finished gem.
Symmetry
The relationship of the height of a gem’s crown to the depth of its pavilion, judged by viewing its profile.
Crown-height to pavilion-depth ratio
Which colored stone variety has cutting challenges due to vulnerable cleavage planes?
Topaz, spodumene and tanzanite.
Excessive bulge on a step cut
A. adds weight.
B. adds beauty.
C. increases brilliance.
D. makes mounting easier.
Excessive bulge on a step cut
A. adds weight.
