Burma Natural Ruby

Buying this stone

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

The deposit

Mogok is a marble-hosted deposit, and that geology is the whole reason Burmese ruby is priced the way it is. Marble carries very little iron, and iron is what quenches fluorescence in corundum. A Mogok stone therefore keeps a red glow under daylight and under ultraviolet that basalt-hosted rubies from Thailand and Cambodia cannot produce, because their iron shuts it down. The practical effect is that this stone reads brighter across a room than its colour grade alone would predict. The same low-iron chemistry leaves fine rutile silk in the crystal, which is the texture a grader looks for to confirm the stone has never been heated.

This stone

At 3.10 carats this is a centre stone. Unheated Burmese ruby is priced on a curve that steepens sharply rather than smoothly: the step from two carats to three is a much larger jump in price per carat than the step from one to two, because clean unheated Mogok rough that finishes above three carats is scarce enough to be traded by reputation. Plan the mount around the stone rather than the other way round. Recutting to seat it in an existing setting will take weight off a stone whose value is concentrated in the fact that it reached this weight at all.

Treatment

Around nine rubies in ten on the open market are heated, and the honest ones say so. This one is not, which is the single most consequential claim on the page and the reason it sits in a different price bracket from a heated stone of the same colour. The treatment to be genuinely afraid of in Burmese-labelled material is lead glass filling, where fracture-riddled corundum is impregnated with high-lead glass to fake clarity. It is worth a small fraction of untreated material and an ordinary jeweller’s torch can damage it during setting.

The report

A IGI report is held for this 3.10 cts ruby 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

• Under a loupe, look for fine rutile silk still intact. Heating dissolves it, so its survival is positive evidence rather than a defect.
• Tilt the stone under a single warm light and check the red holds instead of going brown or grey at the edges.
• Ask whether the report was issued on the stone loose. A ruby graded loose and then set can be substituted between the two events.

Read next

Manikya, the ruby 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.