GIA GG cheat sheet

The 4Cs are Color, Clarity, Cut, and Carat weight; GIA color and clarity grades are determined on the loose, unmounted stone, face-down for color, under controlled lighting and neutral grading environment.

Color scale runs D (colorless) to Z (light yellow or brown); D–F colorless, G–J near colorless, K–M faint, N–R very light, S–Z light. Masterstones are compared against the pavilion.

Clarity grades: Flawless, Internally Flawless, VVS1/VVS2, VS1/VS2, SI1/SI2, I1/I2/I3. FL requires no inclusions or blemishes at 10x; IF allows surface blemishes only.

10x loupe is the standard magnification; clarity is judged by nature, size, number, position, relief, and effect on durability or brilliance.

Cut grade (D–Z round brilliants) combines brightness, fire, scintillation, weight ratio, durability, and polish/symmetry; cut is the factor most influenced by the cutter.

Girdle descriptions range from extremely thin to extremely thick; very thin girdles risk chipping, extremely thick girdles add unnecessary weight without brilliance.

Culet size is graded None, Very Small, Small, Medium, Slightly Large, Large, Very Large, Extremely Large; a large culet is visible as a dark spot through the table.

Fluorescence grades None, Faint, Medium, Strong, Very Strong, and is described with color (blue is most common); strong blue can sometimes create a hazy or milky appearance.

Carat is a weight measure (1 ct = 0.20 g = 200 mg = 100 points); price per carat rises disproportionately with size because large rough is rarer.

Colored stone value is driven by hue, tone, saturation, clarity, cut, and carat weight, in that order of importance for most stones; hue is the dominant factor.

Hue is described with a spectral modifier plus principal hue (e.g., slightly purplish red); tone ranges very light to very dark; saturation ranges from grayish/brownish to vivid.

GIA colored stone clarity types: Type I (usually eye clean: aquamarine, topaz), Type II (usually included: sapphire, ruby, tourmaline), Type III (always included: emerald, red beryl).

Clarity grades run from Eye Clean through SI, MI, VI, and to Included, with type-specific expectations; emeralds are graded more leniently than Type I stones.

Cut quality in colored stones is judged by face-up appearance, symmetry, and retention of weight; windowing and extinction reduce value.

Treatments must be disclosed: heat (sapphire, ruby), fracture filling (emerald), irradiation (blue topaz), diffusion, and dyeing. Untreated stones command premiums.

Phenomenal stones include star sapphire and star ruby (asterism), cat's-eye chrysoberyl, moonstone (adularescence), opal (play-of-color), and labradorite (labradorescence).

Color-change stones (alexandrite, color-change sapphire) shift hue under different light; alexandrite changes green to red, sapphire blue to purple.

Hardness (Mohs) matters for wear: diamond 10, corundum 9, topaz 8, quartz 7, opal 5.5–6.5; cleavage and toughness affect durability independently of hardness.

Refractive index (RI) is measured with a refractometer and read as a range for birefringent stones (e.g., corundum 1.762–1.770); isotropic stones show a single value.

Birefringence is the difference between the high and low RI; it is diagnostic (e.g., quartz 0.009, corundum 0.008, zircon 0.059).

Optical character is singly refractive (isotropic), doubly refractive (anisotropic, uniaxial or biaxial), or aggregate; the polariscope shows strain, and anomalous double refraction appears in some isotropic stones.

Pleochroism (dichroism/trichroism) is observed with a dichroscope; it helps distinguish stones of similar color and confirms anisotropic character.

Specific gravity (SG) is measured with a hydrostatic balance: SG = weight in air / (weight in air − weight in water). Quartz 2.65, corundum 4.00, diamond 3.52.

Spectroscope reveals absorption spectra; characteristic bands (e.g., chrome lines in ruby, rare-earth bands in some garnets) support identification but are rarely conclusive alone.

Magnification reveals inclusions and growth features: curved striae suggest flame fusion synthetic, natural inclusions suggest natural origin, and flux inclusions suggest flux-grown synthetic.

UV fluorescence helps separate natural from synthetic and treated stones; some diamonds fluoresce blue, and certain synthetics show distinctive patterns.

Common simulants: cubic zirconia (RI 2.176, SG 5.6–6.0), moissanite (RI 2.65–2.69, strong doubling), and glass (low RI, singly refractive, gas bubbles).

Pearl types: natural, cultured (Akoya, South Sea, Tahitian), freshwater, and imitation; culturing uses a mantle-tissue piece and, for bead-nucleated pearls, a nucleus.

Grading factors: nacre thickness, luster, surface quality, shape, color, and size. Luster is the most important value factor for appearance.

Luster is described as excellent, very good, good, fair, or poor, judged by the sharpness of reflections on the surface.

Shape categories: round, near-round, oval, button, drop, baroque, and circled; round commands the highest premium.

Color includes bodycolor and overtone; Akoya often show pink or green overtones, Tahitian pearls range from light gray to black with green or peacock overtones.

Surface quality is judged by blemishes, spots, and irregularities visible at normal viewing distance; fewer and smaller blemishes raise the grade.

Nacre thickness matters for durability: thin nacre can crack or show the bead; saltwater pearls are usually bead-nucleated, freshwater often tissue-nucleated.

Pearl size is measured in millimeters; larger pearls are rarer and more valuable within a type. Matching strands requires consistency in size, color, luster, and shape.

Imitation pearls are glass or plastic beads coated with lacquer; they show a smooth, uniform surface and no drill-hole irregularities, and are tested by tooth test or magnification.

Precious metals: gold (24k pure; 18k = 75% gold; 14k = 58.3%; 10k = 41.7%), platinum (usually 950 or 900 purity), silver (925 sterling), and palladium.

Gold alloys are described by karat and color (yellow, white, rose); white gold is usually rhodium plated for a bright white finish.

Setting types: prong (exposes the stone), bezel (protects the stone), pavé (many small stones set closely), channel, and tension; setting choice affects durability and appearance.

Jewelry care: avoid ultrasonic cleaning for fracture-filled, treated, or soft stones; pearls and opals should not be soaked or exposed to heat or chemicals.

Sales process: greet, discover needs, present, handle objections, close, and follow up; discovery questions identify budget, occasion, and style preferences.

Objection handling uses acknowledgment, clarification, and evidence; feature-benefit selling links a product attribute to a customer benefit.

Disclosure and ethics: treatments, synthetics, and simulants must be disclosed; the salesperson should never misrepresent origin or treatment.

Jewelry insurance and appraisals: replacement-value appraisals differ from fair-market value; recommend reappraisal periodically and keep documentation.

Customer follow-up builds repeat business; warranties and return policies should be explained clearly at the point of sale.