How a diamond tester works
A standard "diamond tester" is a thermal conductivity probe. Diamond conducts heat exceptionally well — far better than glass, cubic zirconia or most gemstones. The tester pushes a tiny amount of heat into the stone and measures how fast it moves through. Diamond passes; simulants like cubic zirconia fail.
Why lab-grown diamonds pass
A lab-grown diamond has the same crystal structure and the same thermal conductivity (roughly 900–2,320 W/mK) as a mined diamond, because it is the same material — pure carbon in a cubic lattice. To a diamond tester there is no difference at all. This is not a loophole; it is simply what a diamond is. For the full science, see are lab-grown diamonds real diamonds?
The one caveat: moissanite
Moissanite (a diamond simulant) also conducts heat well and can pass a basic thermal-only tester — which occasionally causes confusion. That's why modern testers add an electrical conductivity check: diamond and moissanite behave differently electrically, so a "diamond & moissanite tester" tells them apart instantly. A lab-grown diamond reads as diamond on both. Learn the difference in lab-grown vs moissanite vs cubic zirconia.
The only proof that actually matters
A pocket tester is a quick sanity check, not certification. The definitive proof of what a stone is — and its exact 4C quality — is the independent IGI certificate. Every Vaima diamond ships with an IGI certificate number you can verify yourself at igi.org, which states it is a laboratory-grown diamond and lists its Cut, Colour, Clarity and Carat. Here's how to read an IGI certificate.