pricescope
Ideal_Rock
- Joined
- Dec 31, 1999
- Messages
- 8,266
This thread continues previous discussions:
GIA EX: Let the buyer beware...
GIA Ex: The Consumers Perspective and the Technologies
Serg gave me a brief lecture, which I'm trying to summarize here.
1. One have to understand why diamond looks bright
Small change in pavilion angle 0.8° significantly rotates out-coming rays (see picture below). As a result, diamonds of certain proportions won’t reflect light from the source into observer eyes in this particular setting while still reflecting light from the sources under different angles.
It was illustrated earlier here: https://www.pricescope.com/community/threads/how-lighting-can-influence-on-grade-appearance.38583/page-2
5. Conclusion:
GIA EX: Let the buyer beware...
GIA Ex: The Consumers Perspective and the Technologies
Serg gave me a brief lecture, which I'm trying to summarize here.
1. One have to understand why diamond looks bright
- Floor is darker than ceilings. If you look at the ceilings directly, ceilings don't look bright. However, take a small mirror, point to the ceiling – you’ll see bright ceilings in the mirror on the floor background. Ceilings reflected in the mirror on dark background (floor) appear bright.
- To see bright flashes from a diamond background should be much darker than secondary or primary light sources. In consumers light condition most light sources are much more bright than background (floor).
- In real life background is much darker than other light sources and light coming from light sources of different brightness and from different angles. Such bright light sources cover big (or biggest) part of upper hemisphere.
- In DiamondDock white walls are very close to the bright light source therefore the background is some orders of magnitude brighter than in reality. This causes the main difference between real life environment. Balance between background brightness and more bright light sources in Diamond Dock is incorrect. A few light sources has brightness stronger than background, such light sources cover small part of the upper hemisphere.
- In this environment, human eyes adjust to the bright background and the only flashes/reflections that will be visible in diamonds come directly from the light source. All other reflections will be much darker than the background and therefore invisible to the human eye.
- Angular size of the light source is relatively small (few degrees). Therefore, only selected group of cuts will benefit from this particular lightning setting. (Even Brilliant Scope has 5 light source positions.) This skews the results toward certain group of diamonds that look good in this particular environment without guarantee that these diamonds will look good in real live and vice versa.
- Pros: standardized environment - all other light sources won’t affect the results.
- Cons: diamonds only take light from narrow light angle. Prefers certain group of diamonds that selectively reflect light from the light source in that specific angular schema.
Small change in pavilion angle 0.8° significantly rotates out-coming rays (see picture below). As a result, diamonds of certain proportions won’t reflect light from the source into observer eyes in this particular setting while still reflecting light from the sources under different angles.
It was illustrated earlier here: https://www.pricescope.com/community/threads/how-lighting-can-influence-on-grade-appearance.38583/page-2
5. Conclusion:
- Selecting correct (close to real live) lightning environment is crucial for adequate diamond cut grading. This includes brightness and angular positions of the light sources as well as brightness of the background. There are several real live lightning environments and different diamonds can look better in some of them and vice versa.
- Any method of light performance evaluation with fixed angular position(s) of the diamond and light source(s) (including GIA DD, Brilliancescope, Imagem, etc) should suffer from this problem by favoring diamonds of certain proportions.
- In theory it is possible to design evaluation devices to favor any set of specific proportions.