A few times a week somebody sets a ring on the counter and says some version of: "It's real — it passed the tester." They mean the pen-shaped gadget you can buy online for the price of lunch. Touch the tip to the stone, it beeps, a light goes green. And they are usually right. The stone usually is a diamond. The problem is what the tester can't tell them, and that gap has gotten expensive.
What a diamond tester actually measures
A basic diamond tester doesn't see the stone. It measures how fast heat moves through it. Diamond conducts heat extraordinarily well — better than most metals — while glass and cubic zirconia barely conduct it at all. So the tip warms up, the tester watches how quickly the stone pulls that heat away, and if the answer is "very fast," it says diamond. That is the whole test.
It's a fine test for what it was designed for: separating diamond from glass, CZ and most other imitations. It was not designed for the two questions that matter most today.
Problem one: moissanite passes
Moissanite is silicon carbide, a lab-made stone sold as a diamond alternative for decades. It also conducts heat very well. Touch a thermal tester to moissanite and you get the same beep. That's not a defect in your tester; it's physics. Better handheld units add a second test, electrical conductivity, because moissanite generally conducts electricity and diamond generally doesn't. A dual tester catches most moissanite. A single-mode thermal pen won't, no matter what the listing promised.
A plain loupe helps too. Moissanite is doubly refractive, so under magnification the back facets often look doubled, like a print that's slightly off-register. Diamond is singly refractive and stays crisp.
Problem two: lab-grown diamond passes everything, because it is diamond
A lab-grown diamond isn't an imitation. It's carbon in the diamond crystal structure, grown in a chamber instead of in the earth. Same hardness, same brilliance, same thermal conductivity, same electrical behavior. Every pen tester ever made will call it diamond, and the tester is correct. There is no counter gadget that separates a lab-grown stone from a mined one by touch. That takes a screening instrument built for the job — the kind that reads how the stone responds to ultraviolet light — or a grading lab.
Meanwhile the price gap has become the whole story. A lab-grown stone of the same size and grade sells for a fraction of a natural one, and that fraction has been shrinking for years. So "it passed the tester" now leaves open the single question that most changes the number: which kind of diamond is it? We wrote up the differences in lab-grown vs. natural diamonds; this post is about how anyone can tell.
How we actually answer it at the counter
Three things, in order.
The girdle. Many graded diamonds — natural and lab-grown — carry a laser inscription on the girdle, the thin edge between the top and bottom of the stone: a lab's initials and a report number, readable under magnification. Lab-grown stones inscribed by the major labs are marked as lab-grown right there on the stone. If the girdle is buried under a bezel or heavy prongs, we may not be able to read it without pulling the stone, which we won't do at the counter.
The paper. A grading report from GIA, IGI, GCAL and a few others states plainly whether the stone is natural or laboratory-grown, and the inscription ties the paper to the stone. Right now, if you search our store for "diamond," you get about ninety listings. Exactly one has "GIA" in the title: an 18K white gold three-stone ring, 13.1 grams, with a report for each stone. Exactly one says "lab grown": a 14K white gold bracelet carrying about seventeen carats total weight. It's labeled that way because the origin is known, and it's priced that way. That is the point of labeling.
The uncertainty. When a stone has no inscription, no paper and a mounting that hides the girdle, we don't guess. Uncertainty gets priced. That isn't us being difficult — it's the only honest way to buy a stone whose origin can't be established on the spot, and it is why the same ring can get a noticeably better offer when it arrives with its report than when it arrives bare.
If you're selling a diamond
- Bring every piece of paper the stone ever came with — the grading report above all, plus the receipt and any appraisal. The report matters most; a jeweler's appraisal is a different document with a different job.
- Leave the stone in the mounting. A loose stone is harder to connect to its history, and the mounting is gold we're buying anyway.
- If you know it's lab-grown, say so. It saves everyone a step, and it changes nothing about the gold — the scale doesn't know what's gold, and it doesn't know what's diamond either.
- Don't buy a pen tester to prove it to us. We'll test it in front of you, free, and show you what we see. The rest of the process is in how to sell or pawn a diamond ring.
If you're buying one
- Ask whether a stone is natural or lab-grown before you ask about the price. A low price on a big stone is usually the answer to that question.
- Ask to see the inscription under the loupe and match the number to the report.
- Lab-grown is a perfectly good thing to buy — a bigger, cleaner stone for the money — as long as you're paying lab-grown prices and you understand you won't get natural-diamond resale for it later. The 4Cs still decide the rest.
Our engagement rings and rings are in the case at the shop; ask and we'll put any stone under the loupe with you.
The tester isn't wrong. It's just answering a question nobody asks anymore. "Is it a diamond?" was the hard question for a hundred years. Now the hard question is "which diamond?", and no beep answers that.
Visit DD Pawn Loans in Pompano Beach
DD Pawn Loans is at 2751 W Atlantic Blvd #101, Pompano Beach, FL 33069. Call or text (561) 774-9292. Hours: Mon–Thu 10am–7pm, Fri 9am–8pm, Sat 10am–7pm, closed Sunday. We buy diamonds and gold outright, and collateral loans are available with no credit check.