Melee is the weak point in diamond provenance, and for a structural reason: individual certification is uneconomic below about 0.30 ct. A parcel of four thousand stones has no documents attached to any single one of them. It has a description on a packet and a supplier's word behind it.
That is fine when the chain is short and known. It is not fine when goods have passed through four hands, each adding margin and losing information.
How mixing actually happens
Rarely as outright fraud at the top. Far more often it happens in the middle, in small quantities, through indifference:
- A house cuts both natural and lab-grown goods on the same floor, and a tray gets moved.
- A parcel runs short and is topped up from whatever matches visually.
- Goods are bought in to fill an order and resold without screening, because screening costs money and the seller assumed.
The stones themselves give nothing away. A well-made CVD or HPHT melee stone is indistinguishable from natural to the eye, under a loupe, and to most standard gemmological testing. Thermal conductivity testers — the pen-style probes — do not separate them, because lab-grown diamond is diamond.
What actually detects it
Melee screening instruments. These are purpose-built devices that pass a parcel through automatically and sort it into "natural", "refer for further testing" and, usually, "simulant". They work on spectroscopic signatures — nitrogen absorption patterns and fluorescence behaviour that differ between stones grown over geological time and stones grown in a fortnight.
Two things worth knowing about them. First, they are fast: several thousand stones an hour on the machines used by larger laboratories and manufacturers. Second, they are deliberately cautious — a stone flagged as "refer" is not condemned, it simply needs a laboratory to look at it. In practice a small referral rate is normal and is not evidence of mixing.
What to require from a supplier
- Ask whether they handle lab-grown goods at all. A house that does not have synthetic material in the building cannot mix it in by accident. That is a stronger control than any procedure applied to a floor that handles both.
- Ask who cut the goods. If your supplier did not manufacture them, ask how far back they can trace them. Vagueness here is the signal.
- Ask for the warranty statement on the invoice. The System of Warranties declaration should be on every invoice, and it is what your own compliance file is built from.
- Screen incoming goods, or ask for pre-dispatch screening. If you buy melee in volume, a screening instrument pays for itself in avoided argument. If you do not, ask the supplier to arrange it — a supplier confident in their goods will not object.
Disclosure, not prohibition
None of this is an argument against lab-grown diamonds. They are a real product with real demand, and houses that sell them clearly labelled are doing nothing wrong. The industry problem is disclosure, and the size at which disclosure is hardest is melee.
If a supplier cannot tell you whether synthetic material has ever been in the same room as your parcel, they are not answering the question — they are hoping you stop asking it.
Our position
We manufacture natural diamonds only. We do not cut, stock or trade lab-grown goods, so there is no separate line and no route by which synthetic material could reach a natural parcel here. All rough entering the floor arrives under Kimberley Process certification, and every invoice carries the warranty statement.
You should not take that on trust, and we would rather you did not. Screen our goods. If you would like a parcel screened before dispatch, ask and we will arrange it at cost.