Sri Lankan Blue Sapphire

Buying this stone

Where it came from, what its weight band is for, and what to check before any money changes hands.

The deposit

Sri Lankan sapphire is recovered mostly from illam, the gem-bearing gravel layers worked around Ratnapura, rather than from hard rock. The material is metamorphic and generally lower in iron than basalt-hosted sapphire from Australia or Thailand, which is what gives Ceylon stones their lighter, more open blue and keeps them from closing up under weak light. The island has also produced fine sapphire continuously for well over two thousand years, so the cutting tradition around it assumes large stones and cuts to keep them rather than to a fixed template.

This stone

At 9.23 carats this is a substantial stone, and Ceylon is the source that reliably produces blue sapphire at this weight with the colour still even through the pavilion. That is the specific difficulty above about five carats: a deeper stone shows more of its own colour to the eye, so a saturation that looks correct in a three carat cushion can read too dark at nine. This one is cut as a cushion, which spreads the weight across the face rather than driving it into depth, so it presents closer to its carat weight than a deep oval of the same size would.

Treatment

This stone is heated. That is the ordinary, permanent, universally accepted treatment for sapphire, it is disclosed here rather than left for a laboratory to tell you later, and the price reflects it. An unheated stone of the same colour and weight would cost several times more, and much of the trade’s stock at this size would not exist at all without heat. What heating is not is diffusion. Beryllium or titanium lattice diffusion drives colour in from the surface, is a separate disclosure entirely, and is materially cheaper material than heated stone.

The report

A IIGJ report is held for this 9.23 cts blue sapphire and is handed over with it. Verify the number with the laboratory rather than only with us, and check its weight against the stone before money moves.

Before you pay

• Ask specifically whether any diffusion is present, not just whether the stone is treated. The two words are used loosely and mean very different prices.
• Look for straight or angular colour banding through the side of the stone, which tells you how evenly the blue is distributed.
• Check the blue under warm indoor light as well as daylight. A stone that closes to near black indoors will do that every evening you wear it.

Read next

Neelam, the blue sapphire covers the material itself and what gets sold in its place. How to buy a coloured stone covers pricing, treatment and reports.

Written by Kamal Kishore Agarwal, founder and gemmologist, Gem-A qualified, buying in Johari Bazaar since 2008.