RESOURCES
How to Judge CVD Rough: Five Key Dimensions
Color, clarity, crystal form, size and certification — five dimensions for evaluating CVD rough and avoiding low-grade material.
01Color
Gem-grade rough is best at D/E/F colorless. CVD rough with excess nitrogen turns yellowish; boron turns it blue. Quality MPCVD precisely controls gas ratios and impurities to stably produce D/E color. Observing body color under natural light is the most direct first step.
02Clarity & Inclusions
Common CVD inclusions are graphite spots, needles and layered growth lines. High-clarity (VVS/VS) rough is clean inside with no obvious dark spots. Examining internal stress lines and inclusion distribution under a polariscope is key to predicting whether a high-clarity polished stone can be cut.
03Crystal Form
Quality rough has an intact crystal form, sharp edges and few defects, giving a higher yield. Standard rectangular rough (e.g. 20×15×9.5mm) is easier to orient for cutting with better utilization. Distorted or porous rough leads to higher cutting loss and lower yield.
04Size & Weight
At equal quality, larger size is rarer. Large rough (30×30×15mm and above) yields large-carat polished stones at higher unit value and scarcity. ENTASK's main rough spans 20×15×9.5 to 35×35×12mm. To be precise about records: public reporting contains larger carat figures than this — a 190 ct CVD crystal, and on the HPHT route a 150.42 ct crystal at 28.55×28.25×22.53 mm analysed by IGI — each at a different grade, shape and evidence level, so "largest" means nothing detached from a stated grade and measure. 35×35×12 mm is the largest format ENTASK has delivered at D-E colour, VVS-VS clarity, Type IIa (company-supplied, not independently verified).
05Certification & Traceability
Authoritative certificates (IGI, GIA) back up quality. A reliable supplier should provide per-batch certificate samples stating weight, color, clarity, cut, fluorescence and growth method (CVD). ENTASK rough can be IGI-certified — Type IIa, no fluorescence, CVD-grown.
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