Diamond is crystalline carbon, the stone of Venus (Shukra) in the Navratna, and the most thoroughly documented gem in the world — grading systems, inscriptions and laboratory reports are the norm for anything above a fraction of a carat. That infrastructure exists because diamond is also the most valuable per gram and has the most sophisticated substitutes: not just simulants but laboratory-grown diamond that is diamond in every physical respect.
What diamond is
Carbon in the cubic crystal system. Properties: RI 2.417 (over the refractometer limit), SG 3.52, hardness 10, singly refractive, dispersion 0.044, extremely high thermal conductivity, adamantine lustre, usually Type Ia (nitrogen-bearing). About a third fluoresce blue under long-wave UV.
Three separate questions
Is it diamond? Separates diamond from cubic zirconia, moissanite, white sapphire, glass and other simulants. Thermal and electrical conductivity, doubling (moissanite), SG (CZ) and dispersion decide it in minutes. Diamond, moissanite and cubic zirconia.
Is it natural or laboratory-grown? Grown diamond passes every simulant test. Screening by UV fluorescence patterns, phosphorescence, type classification and strain patterns refers suspect stones; confirmation needs spectroscopy. Lab-grown diamonds (HPHT and CVD).
Has it been treated? HPHT colour enhancement, irradiation (colour), laser drilling (to bleach dark inclusions, leaving a fine tunnel), fracture filling (glass in cleavages, showing a flash effect), and coating. Each must be disclosed; laser drilling and fracture filling in particular affect durability and value.
Grading: the four Cs as designed for diamond
Colour — graded on a scale from colourless (D) downward through near-colourless to light yellow or brown, by comparison with master stones under controlled light. Fancy colours (blue, pink, yellow of saturation) are graded separately.
Clarity — from Flawless through VVS, VS, SI to Included, based on the size, number, position and visibility of inclusions at 10×.
Cut — proportions, symmetry and polish, graded from Excellent to Poor for round brilliants; fancy shapes graded for polish and symmetry.
Carat — weight, measured. Price per carat steps up at the popular weight boundaries (0.50, 1.00, 1.50, 2.00 ct).
These grades are the substance of a diamond grading report, which differs from an identification report in giving quality grades as its main content. Grading is standardised but still involves judgement; two laboratories can differ by a grade.
Inscriptions and matching
Most graded diamonds are laser-inscribed on the girdle with the report number, visible at 10×. Matching the inscription to the report, and the report's weight and measurements to the stone, is how a buyer confirms that the document and the stone belong together. An inscription can be added or removed; the measurements are the check. Matching the report to the article in your hand.
What a routine laboratory can do
Confirm diamond versus simulant; screen for laboratory growth and refer where indicated; detect laser drilling, fracture filling and most coatings; give an opinion on colour and clarity. Definitive natural/grown determination and formal grading to an international scale are the province of specialised diamond laboratories, and a general report should say so.
Frequently asked questions
Will a diamond tester prove a diamond is natural?
No. It proves the stone is diamond (or moissanite, if thermal-only). Natural versus grown needs different tests.
Is a lab-grown diamond acceptable as heera?
That is for the wearer's tradition. The laboratory's role is to state which it is.
Does fluorescence lower a diamond's value?
Strong blue fluorescence can slightly lower value in high-colour stones and is neutral or positive in lower colours. It is noted on reports.
What is "fracture-filled" diamond?
A diamond with surface-reaching cleavages filled with lead glass to hide them. It shows a flash effect, is less durable, and must be disclosed.
Can a small diamond be tested?
Yes, though very small stones (melee) are usually screened in batches for laboratory growth rather than individually reported.