Diamonds

Macle

A flat, triangular contact-twinned diamond crystal

prism images of inclusions

Can be seen multiple times when viewed from adjacent facets

mirror reflections of inclusions

Can be seen twice when viewed from the opposite facet

spherical aberration

Optical flaw where light rays passing through the side of a curved lens focus at a different point than rays passing through the middle of the lens. Straight lines appear to bend.

chromatic aberration

Optical defect where a lens fails to focus all colours of light to the same point resulting in a rainbow effect around the viewing field.

The GIA clarity grading system is based on which 5 factors?

1. number

2. size

3. location

4. relief (contrast)

5. nature (type)

…of the inclusions.

The 10x triplet loupe has which 3 components?

1. Magnifying lense

2. Color correcting (achromatic) lens

3. Linear correcting (aplanatic) lens

Xtl

Crystal (incorrect: “bubble”)

Ndl

Needle

PP

Pinpoint

Cld

Cloud

TW

Twinning Wisp

Ftr

Feather (sometimes: “gletz”)

IG

Internal Graining

GC

Grain Center

EC

Etch Channel

BG

Bearded Girdle

Br

Bruise (sometimes: “percussion mark”)

K

Knot

Patch

Patch of Color

Ch

Chip

Cav

Cavity

IN

Indented Natural

LDH

Laser drill hole

ILD

Internal laser drilling

Fracture filling

Treatment that involves injecting a molten glass substance into a diamond’s surface reaching feathers or drill holes to make the characteristic less apparent. GIA does not grade fracture filled diamonds because the treatment is not permanent. Tell-tale sign?

Flash effect

A flash of colour which changes to a second colour when you tilt the stone.

Nck

Nick (blemish)

Abr

Abrasion (blemish)

Scr

Scratch (blemish)

EF

Extra facet (blemish)

LS

Lizard skin (blemish)

PL

Polishing lines (blemish)

Brn

Burn (blemish)

RG

Rough girdle (blemish)

Pit (blemish)

Small opening often accompanied by drag lines. Result of PP inclusion removed during polishing.

LMR

Laser manufacturing remnant. Can be blemish (surface groove) or inclusion (surface reaching fracture).

N

Natural (blemish)

SG

Surface graining (blemish)

Callable inclusion

Affects the clarity of the diamond and can be seen at 10x magnification

Non-callable inclusion

Does not affect the clarity and can therefore also exist on a flawless diamond

FL

Flawless

• no inclusions or blemishes at 10x EXCEPT:

— extra facets not visible face up at 10x

— Naturals (N) confined to the girdle as long as they don’t thicken the girdle or distorted its outline

— internal graining (IG) if not it’s reflective, white, coloured and doesn’t affect transparency

— inscriptions that are not internal and do not penetrate at 10x

— mounting features

IF

Internally Flawless

• only insignificant blemishes and no inclusions at 10x

— same features allowed as FL

— Normally, the blemishes on an IF diamond can be removed by very minor repolishing except for surface graining because this cannot be polished away

VVS

Very very slightly included

• contain minute inclusions very difficult to see at 10x

— inclusions in VVS1 are extremely difficult to see face up, might only be visible through pavilion

— very difficult to see in VVS2

— A typical VVS1 stone might show a pinpoint or two, or reflective internal grinding that’s visible only through the pavilion or very faint through the crown

— if these characteristics show of more clearly through the crown, the stone would get a VVS2 grade

VS

Very slightly included

• minor inclusions that range from difficult (VS1) to somewhat easy (VS2) to see under 10x

— All types of clarity characteristics possible

— Grade depend depends on overall visibility when considering all five grading factors

— typical inclusions are small crystals, knots, distinct clouds, or minor surface-reaching inclusions such as feathers, cavities, or indented naturals.

SI

Slightly included

• noticeable inclusions that are easy (SI1) or very easy (SI2) to see at 10x

— All types of clarity characteristics possible

— Grade depends on overall visibility and considering all five grading factors

— most of the time the characteristics in an SI1 diamond are not visible face up without magnification

— Eye-visible inclusions are more often seen in an SI2 diamond

— typical inclusions include crystals, feathers, clouds and twinning wisps

I

Included

• obvious conclusions at 10x

— Can be seen face up without magnification

— Seriously affect the stone’s durability

— Numerous or large enough to affect the transparency and brightness

— Often rough at this clarity level is used for industrial purposes

Proportions of a diamond

Proportions are the angles and relative measurements of a polished gem and the relationship between them.

→ Play a key role in the diamond’s light performance and appearance.

Polish

The overall condition of the facet surfaces of a finished diamond.

Symmetry

The exactness of a finished gem’s shape and the placement of its facets.

How can a diamond’s cut grade be estimated?

By visually evaluating its brightness, pattern and fire.

Scintillation

The dynamic sparkle, twinkle, and pattern of light-and-dark flashes you see when the diamond, the light source, or your eyes move.

Fire

A diamond’s display of dispersion.

Refractive Index

A measure of the change in speed and direction of light as it travels from the air to a certain material.

Average Girdle Diameter

(minimum girdle diameter + maximum girdle diameter) ÷ 2

Total Depth Percentage

(depth ÷ Average Girdle Diameter) x 100

Table-to-Culet depth. Expressed as % of average girdle diameter.

Well proportioned diamonds typically have total depth percentages around …?

60%

Diamonds with total depth percentages below … % are generally underweight?

55%

Diamonds with total depth percentages of …% or more are generally overweight?

65%

Table percentage

The size of a diamonds table is expressed as a percentage in relation to its average girdle diameter.

Most between 55 - 65%

The crown angle on a diamond is ideally between … and … degrees?

25 - 35°

A crown height percentage of …% and above is considered deep?

18.5%

ETN girdle

Extremely thin girdle

Knife-edge at 10x

VTN girdle

Very thin girdle

Very thin line at 10x

THN girdle

Thin girdle

Thin line at 10x

MED girdle

Medium girdle

Distinct line at 10x

STK girdle

Slightly thick girdle

Obvious at 10x

THK girdle

Thick girdle

Very obvious at 10x

VTK girdle

Very thick girdle

Distracting at 10x

ETK girdle

Extremely thick girdle

Very distracting at 10x

Design

A diamond’s physical shape, including its proportions and durability.

Finish

The quality of the polish and precision of the cut of a fashioned gemstone.

OR

Out-of-Round

The girdle outline doesn’t look perfectly round.

T/oc

Table off-center.

The table is not centered in the crown

C/oc

Culet off-center.

The culet is not centered in the pavilion.

T/C

Table/Culet alignment.

Table and culet are displaced in opposite directions.

GTV

Girdle thickness variation.

Variations in the girdle thickness

CV

Crown angle variation.

Variation in measurements of all eight crown angles. Typically related to T/oc

CHV

Crown height variation.

Variation in the diamond’s eight crown height measurements

SV

Star angle variation.

Unequal star facet angles

PV

Pavilion angle variation.

Variation in measurements of all eight pavilion angles. Typically related to C/oc

SPV

Star percentage variation.

Variation in the diamond’s eight measured star facet length percentages

UHP

Upper half variation.

Unequal upper half facet angles

LPV

Lower half percentage variation.

Variation in the diamond’s eight measured lower half facet length percentages

LHV

Lower half variation.

Unequal lower half facet angles

MF

Missing facet.

A facet that should be in a given location is absent

EF

Extra facets

Facets not required by the cutting style are placed without regard for the diamond’s symmetry

T/oct

Non-octagonal table.

The table doesn’t have eight sides of equal length and parallel opposing sides. This results in star and bezel facets that are also misshapen.

Fac

Misshapen facets.

Facets are not properly shaped or they’re not the same size and shape as others of the same type

Ptg

Non-pointing.

Facets failed to meet at precise points or a fully formed facet doesn’t reach its prescribed location

Aln

Misalignment.

Crown and pavilion facets not aligned with each other

Beneficiaton

A commitment to reserve a portion of the resources derived from a country for its economic development.

Central Selling Organisation (CSO) , later Diamond Trading Company (DTC)

The marketing and sales arm of De Beers

Downstream

The retail portion of the diamond value chain.

Upstream

The mining and rough distribution part of the diamond value chain.

Bort

Industrial grade diamond, heavily included, yellow, gray, brown

Sight

Rough diamond sales event where long-term customers buy from producers based on contracts.

Vertical Integration

A business strategy of operating in more than one segment of the value chain to make more profit.

Carbonado

An aggregate of many randomly oriented interlocking tiny diamond crystals that is the toughest form of diamond. Used for industrial purposes. Usually opaque, dark, and porous, with a glassy appearance and an irregular surface. Sourced only in Brazil and Central Republic of Africa.

CLIPPIR diamonds

Cullinan-like

Large

Inclusion-Poor

Pure

Irregular

Resorbed

Superdeep diamonds from the transition zone. The carbon comes from an oceanic plate that has been subducted. The growth medium for these diamonds are metallic melts that dissolve the carbon from the oceanic plate.