Almost every sapphire and ruby sold today is bought from a screen — a photograph, a short video, and a certificate. Learning to read those images accurately is the single most useful skill an online gem buyer can develop, because the difference between a well-shot honest stone and a flattered mediocre one is visible if you know where to look. This guide explains what listing photos and videos genuinely tell you, what they exaggerate, and what they can never show.
Why Gemstone Photography Distorts Colour So Easily
Corundum is a strongly coloured, highly refractive material, and cameras handle it badly. Sensor white balance, the colour temperature of the light source, and post-processing saturation all shift a stone's apparent hue — often without anyone intending to deceive. A blue sapphire shot under a cool LED panel will read noticeably more vivid than the same stone under warm halogen, and a pink sapphire photographed against a white background will appear lighter in tone than it does in the hand.
The practical response is not to distrust every image, but to look for consistency across multiple images. A seller who shows the same stone under daylight-equivalent light, under incandescent light, and in a neutral grey or hand shot is giving you enough information to triangulate. A single hero shot on a black background with heavy contrast is giving you almost nothing.
Watch also for the background. Black backgrounds deepen apparent tone and hide extinction; white backgrounds wash out saturation. Neutral grey, or a hand, is the most honest presentation and is what serious dealers tend to use.
Video Is More Honest Than Stills
A still image is one moment under one lighting condition. A video of a stone rotating under a moving light source shows how the gem actually behaves — and that behaviour is where most of the value sits. Watch a 360-degree video and you will see colour zoning appear and disappear, extinction areas move across the crown, and brilliance either flash evenly or die in patches.
Three things to watch for specifically in video:
- Colour stability through rotation. Pleochroic stones shift hue as they turn. A well-oriented sapphire holds its face-up colour; a poorly oriented one flips towards grey or greenish-blue.
- Even light return. The whole face of the stone should light up more or less together. If one half stays dark while the other flashes, the pavilion is likely off-centre or badly angled.
- Movement of inclusions. Video will reveal silk, feathers, or crystals that a still shot at a flattering angle can conceal entirely.
Spotting Windowing and Extinction on Screen
Windowing is the most common cut fault in colored stones and it is highly visible on video. A window is a pale, washed-out area in the centre of the stone where light passes straight through the pavilion instead of reflecting back — usually the result of a shallow cut retained to preserve carat weight from the rough. In a rotating video, a window appears as a see-through patch that stays pale while the rest of the stone flashes.
Extinction is the opposite: dark, dead zones where no light returns. Every faceted colored stone has some extinction, and a modest amount actually adds contrast and life. What you are judging is proportion. If more than roughly a third of the face-up area sits dark through most of the rotation, the stone will look flat and heavy on a finger, regardless of what the colour grade on the certificate says.
Both faults are worth taking seriously because they are permanent. A stone with strong windowing can sometimes be recut, but only at the cost of significant weight — which is precisely why it was cut that way in the first place.
What Photographs Can Never Tell You
No image, however good, establishes treatment status, origin, or true dimensions. Heat treatment is invisible in a photograph; so is beryllium diffusion, so is lead-glass filling in ruby. These are laboratory determinations, which is why a stone of any consequence should come with a report from GIA, GRS, AGL, or Lotus, and why the report number should be verifiable on the lab's own website rather than only visible in a seller's photo.
Millimetre measurements matter as much as carat weight, and photographs distort both. Two 2-carat sapphires can differ by more than a millimetre in face-up diameter depending on how deep they are cut. Always read the stated dimensions rather than judging size from an image, especially when the stone is destined for an existing setting or a calibrated production run.
At Thai Gems we photograph and film every stone in our own Bangkok office under standardised lighting, because after seventy years in the trade we would rather a client see exactly what is arriving than be pleasantly surprised in one order and disappointed in the next.
A Practical Checklist Before You Buy
- Insist on video, not just stills — and video with the stone in motion under a moving light.
- Look for at least two lighting conditions across the listing images.
- Check that the face-up area lights evenly, with no persistent pale window.
- Read the stated millimetre dimensions, not the apparent size in the photo.
- Verify the certificate number directly on the issuing laboratory's website.
- Confirm the return policy in writing before payment — the only true test is the stone in your hand.
Browse Thai Gems' current selection of loose sapphires and rubies — every stone photographed and filmed in-house, with treatment clearly disclosed and certification available. Contact us for trade pricing, additional media on any stone, or custom orders.