London blue is the dark end of blue topaz: deeper, inkier and cooler than the bright Swiss grade, often with a steely or faintly greenish cast that gives it a more serious look. It is the grade people reach for when they want blue topaz that does not read as cheerful.

The stone

12.70 carats, which is 13.96 ratti. Rs. 25,400, Rs. 2,000 per carat, reference GS-BT-0009. Measured against every other blue topaz photograph in our collection, this is the darkest stone we list.

One thing to be straight about: the grade here is our reading of the stone from its own photograph, not a figure recorded on a laboratory document. No routine report assigns a Sky, Swiss or London grade — they are trade descriptions of depth, applied by eye. If the exact shade matters to your design, ask us on WhatsApp at +92 308 887 3888 and we will photograph it under daylight and under indoor light so you can judge it before it ships.

The three grades

• Sky blue — the palest, soft and airy.
• Swiss blue — vivid, saturated, a clean bright mid blue.
• London blue — the deepest, with a steely cast. This stone.

None of the names refers to a place; they describe colour depth, produced by different treatment regimes.

Living with a dark stone

1. Judge it indoors, not at a window. Deep blue looks magnificent in daylight and can close up under a ceiling lamp. Decide using the light you will mostly see it in.
2. Ask for an open back. On a dark transparent stone this matters more than on a pale one — light entering from behind is what keeps it alive rather than black.
3. White metal lifts it. 925 silver, white gold or platinum. Yellow gold deepens a dark blue further, which can be too much.
4. Size works in your favour. At 12.70 carats there is depth for light to travel through, so the colour reads rich rather than opaque.

Where the colour comes from

Blue topaz gets its colour from irradiation and heating — standard for the stone and on our specification sheet. London blue in particular is produced by a more intensive treatment than the lighter grades, which is why it is a consistent product rather than a lucky find. The colour is permanent and the starting material is natural colourless topaz.

Durability

Topaz is 8 on the Mohs scale, but it has perfect basal cleavage — a sharp knock in the wrong direction can split it where no scratch would ever mark it. Never use an ultrasonic or steam cleaner. Warm soapy water and a soft brush. Our topaz care guide has the full routine.

Ordering

One piece only. Shape and measurements have not been recorded; we will measure it on request. Flat Rs. 500 delivery anywhere in Pakistan, insured and tracked, dispatched in one to two working days. Cash on Delivery, seven days to return it unused. Compare the grades in the blue topaz collection.

This particular stone

This listing is one natural blue topaz with a weight of 12.7 Carat. Its price is Rs. 25,400 — roughly Rs. 2,000 for each carat. Treatment: irradiated & heated. Quote reference GS-BT-0009 when you message us about it. The photographs show this exact stone, so what arrives at your door is the piece you chose on screen.

Above twelve carats you are into collector territory. Pieces this heavy are usually set as pendants or kept loose, and they are prized for the size of rough they came from. If you do set it, choose a bezel or a heavy claw to protect the edges.

On the Mohs scale blue topaz rates 8. Few materials will scratch it, so it copes well with everyday ring wear. A soak in warm water with a drop of mild soap and a soft brush keeps it bright; skip the ultrasonic cleaner if inclusions reach the surface.

Whoever you buy blue topaz from, make sure of three things: the stone is natural rather than lab-grown, glass or glass-filled; any treatment is stated in writing; and the weight quoted is the weight of the finished stone. We check every blue topaz for those three points before it is listed, a certificate is available on request, and because you pay on delivery you can look at the stone — or have it tested — before any money changes hands.

We sell natural stones only and inspect each one before it is listed. Treatment for this stone: Irradiated & heated. Certificate available on request. As general background (not a statement about this stone): Blue topaz gets its blue colour from irradiation and heating — this is standard for the stone and the colour is stable. Ask us on WhatsApp and we will tell you what we know about this exact stone; independent lab testing is available on request.

A certificate of authenticity is available on request for this stone, and independent laboratory testing can be arranged. Because you pay on delivery, you can also take the stone to a lab of your choice within the 7-day return window. Read more on our authenticity page.