The Calibration Card
A single printed card with known color anchors is what lets GemMetric™ turn any phone camera into a calibrated colorimeter — and makes readings consistent across every device and lighting.
Why a physical reference matters
Every phone camera renders color a little differently — and the light you shoot under changes it again. Without a known reference in the frame, there’s no way to tell whether a stone’s measured color is real or an artifact of the device. The calibration card solves this: by placing patches of known color next to the stone, the engine corrects for your specific camera and lighting, then measures the stone’s true body color — and the same card in someone else’s hands produces the same grade. That consistency is what makes the trade trust the number. No ordinary color app uses a physical reference standard, because no ordinary color app can — the card is the moat.
This is the same principle lab spectrophotometers use — a known reference sample to calibrate the instrument before each measurement. GemMetric™ brings it to your pocket, so every scan is traceable to the exact card that calibrated it.
What the card does
The card carries a set of reference color patches the engine uses to correct for your camera’s individual color response.
A grayscale reference lets the engine correct tone drift across the lightness range — not just hue.
Geometric markers let the camera lock onto the card’s position and correct for perspective and angle.
Each card carries a unique serial number, read automatically at capture time, linking every grade to the physical reference that calibrated it.
The serial system
Every calibration card carries a unique serial number (format GMC-2026-XXXX), encoded in the QR code and printed on the card. When you scan a stone, the serial is read automatically and linked to the result. That link is what makes a grade auditable — anyone in the trade can verify which physical reference calibrated the capture, so the color behind your decision is never just a claim.
Two card types
Print yourself on a quality inkjet photo paper. Good enough for evaluation and most grading work. Each card carries a unique serial generated when you download.
Best results with matte photo paper at highest quality settings.
Factory-printed on durable plastic substrate with controlled, stable color patches. Higher accuracy and repeatability for professional and lab use.
Serialized in tracked batches with tighter patch tolerances.