An ASET map is a four-color picture that shows from which directions a stone's face-up light comes. It can be part of the AGS Ideal Report by GIA.
In more detail
Red marks the strongest light, from high above. Green marks dimmer light that still adds sparkle, and blue marks the dark contrast areas. Gray marks light lost through the bottom, and a stone that scores well is mostly red. Our simulator's light map uses the same idea, but it is our own render and shows leakage in black.
On a grading report
Only on the AGS Ideal Report by GIA, in the version with the map. For an oval, ask for that version to check for a bow-tie.
Related terms
- AGS Ideal Report by GIA: The AGS Ideal Report by GIA is a digital supplement to a GIA report. It gives the American Gem Society's light performance grade, and only AGS Ideal 0 stones get one.
- Light Return: Light Return sorts each point of a face-up stone by the direction its light came from. Its four classes, direct, indirect, contrast and leakage, together cover the whole face-up stone.
- Leakage: Leakage is light that enters a stone and leaves where the viewer cannot see it, mostly through the pavilion. Lower leakage is better.
- Contrast (Light Return): Contrast is the part of a face-up stone whose light comes from 75° or higher above the girdle plane. This zone lies within 15° of the line of sight, where the viewer's head is.
- Bow-tie: A bow-tie is a dark band across the belly of an oval, pear, marquise or other elongated stone. It is not an inclusion or a color: the facets there send little light back to the viewer.