Quick answer: The best diamond tester for most Indian jewellers is a combined thermal and electrical conductivity tester, which separates diamond, moissanite and simulants in seconds. For busy counters and labs handling lab-grown stones, a dedicated screener such as the J-Mini Pro is the most reliable choice. Budget thermal-only pens work for a first check but cannot flag moissanite on their own.
How diamond testers work
Most handheld testers measure thermal conductivity, because diamond conducts heat better than almost any simulant. The catch is that moissanite conducts heat similarly to diamond, so modern testers add an electrical conductivity probe to tell the two apart. Lab-grown (CVD and HPHT) diamonds are real diamond, so a conductivity tester will read them as diamond; separating natural from lab-grown needs a dedicated screener.
Types of diamond testers by price and use
Entry level (thermal only). Low-cost pen testers confirm whether a stone is diamond versus common glass or cubic zirconia. Good for a quick check at a shop counter, but they cannot detect moissanite. Best for hobbyists and first screening.
Mid range (thermal plus moissanite). Combination testers add electrical conductivity to separate diamond from moissanite. This is the sweet spot for most Indian retail jewellers and buyers who need dependable everyday results.
Professional screeners (natural vs lab-grown). Instruments like the J-Mini Pro screen for lab-grown and treated diamonds, which is essential now that CVD and HPHT stones are common in the Indian market. Best for labs, wholesalers and serious dealers.
What to look for before you buy
Check moissanite detection, accuracy on small melee, ease of use, calibration and warranty support in India, and whether the device handles mounted and loose stones. For high volumes, battery life and a metal-detection alert also matter. Buy from a supplier that offers after-sales support and genuine stock.
Frequently asked questions
Can a diamond tester detect lab-grown diamonds? A standard conductivity tester cannot, because lab-grown diamonds are real diamond and read as diamond. To identify CVD or HPHT stones you need a dedicated screener like the J-Mini Pro.
Will a diamond tester tell diamond from moissanite? Only if it has a moissanite or electrical conductivity function. Thermal-only pens will falsely read moissanite as diamond, so choose a combination tester.
Are cheap diamond testers accurate? Entry-level testers are reasonably accurate at spotting glass and cubic zirconia, but they miss moissanite and struggle with very small stones. For business use, invest in a mid-range or professional model.
Which diamond tester is best for a jewellery shop in India? For everyday retail, a combined thermal and moissanite tester is ideal. Labs and wholesalers handling lab-grown stones should choose a screener such as the J-Mini Pro.
Do diamond testers work on mounted stones? Most do, as long as the probe can touch the stone. Check the tip size and specifications for melee and set stones before buying.
Browse diamond and gem testers at Johari Gems & Tools. We supply jewellers, labs and institutes across India with genuine instruments, expert advice and fast, free shipping within India on eligible orders.