Treatment disclosure is the single most important thing to understand before buying a coloured stone. Here is what each term means and how it affects value.
Heat treatment
Heating corundum to around 1,800 degrees Celsius dissolves rutile needles inside the stone and deepens the blue. It has been standard practice for centuries, it is stable, and it is accepted by every laboratory and every trade body. A heated sapphire is still a real sapphire.
Heating roughly doubles the yield of usable blue from a given parcel, which is why unheated stones of the same colour cost substantially more. We mark treatment status on every listing.
Unheated
A stone described as unheated has not been exposed to heat beyond what it experienced naturally in the ground. Unheated is not the same as untreated in a broader sense — it means specifically that heat was not applied.
Unheated material is rarer and priced accordingly. When we list a stone as unheated, it is because we bought the rough and followed it through cutting ourselves.
Fracture filling
Filling surface reaching fractures with a lead glass or resin improves apparent clarity. It is common in low grade ruby. It is not stable — the filler can be damaged by heat, acid, or ultrasonic cleaning — and it dramatically reduces value.
We do not knowingly sell fracture filled stones. If we ever did, it would be stated in the first line of the description.
Diffusion
Lattice diffusion introduces colouring elements into the surface of a stone at high temperature. The colour is real but shallow. A diffused sapphire can be cut or repolished and lose its colour.
We do not sell diffused material.
Irradiation
Used to turn colourless topaz blue, and sometimes to deepen zircon. It is stable and accepted, but it is a treatment and we disclose it. Blue topaz is almost always irradiated; that is why it is inexpensive.
Certification
An independent report from a gemmological laboratory confirms weight, dimensions, and where relevant, treatment and origin. It does not grade coloured stones the way a diamond report grades colour and clarity — coloured stone reports are descriptive, not graded.
Loose stones above $500 include a report. If you want a report on a stone below that threshold, ask us before you order and we will tell you what it would cost.
Our rule
If we are not certain, we say we are not certain. A stone with an honest question mark over it is worth more than a stone with a false guarantee.