What is the Master-eye effect?

What is the Master-eye effect?

• A. The optical illusion that causes the ungraded diamond to appear either lighter or darker than the masterstone, depending on which side it's on.
• B. A unique type of laser inclusion
• C. A brand name for a polishing technique
• D. The color difference between the girdle and pavilion

Answer: (A)

The Master-eye effect is a perceptual phenomenon that occurs when you compare a diamond to a fixed master stone. Our eyes judge color and brightness relative to the reference, so the ungraded diamond can look lighter or darker than the master depending on which side it sits beside during the viewing. This illusion comes from contrast and lighting interactions with facets and edges, plus the sensitivity of human perception to surrounding context. Because color grading relies on consistent perception, changing the stone’s position, angle, or lighting can flip the impression and bias the result. To minimize it, keep viewing conditions identical for both stones: fixed lighting, the same distance and angle, and a consistent orientation while you compare. It’s a visual artifact, not a true physical difference in the stones.

The Master-eye effect is a perceptual phenomenon that occurs when you compare a diamond to a fixed master stone. Our eyes judge color and brightness relative to the reference, so the ungraded diamond can look lighter or darker than the master depending on which side it sits beside during the viewing. This illusion comes from contrast and lighting interactions with facets and edges, plus the sensitivity of human perception to surrounding context. Because color grading relies on consistent perception, changing the stone’s position, angle, or lighting can flip the impression and bias the result. To minimize it, keep viewing conditions identical for both stones: fixed lighting, the same distance and angle, and a consistent orientation while you compare. It’s a visual artifact, not a true physical difference in the stones.