- Leakage of Light in Diamonds and Its Estimation
- Stereoview: Stereovision and evaluation of leakage
- Taking into account the features of human perception
- Brilliance
- Light Return
- Contrast
Brilliance
Below there are all definitions of "Brilliance" that we could find so far (1), our considerations why so many definitions do exist (2), and two definitions of "Brilliance" that match our understanding of this phenomenon (3). This material is a part of our future article devoted to Brilliance and we will be grateful if you share your considerations, concerns and comments.
1. Definitions of "Brilliance"
- GIA Diamond Dictionary, 3rd edition: Intensity of the
internal and external reflections of white light from the
crown of a polished diamond or other gemstone. Hardness,
refractive index, reflectivity, polish, luster, and proportions
all affect a gemstone's brilliance.
- Diamond Grading ABC by V. Pagel-Theisen, 11th edition:
External brilliance - luster, produced by reflection of
light on the surface of the facets; Internal brilliance
- refraction and total reflection of light on the pavilion
facets; Dispersive brilliance - splitting of scattering
of light into its spectral colors = the dispersion which
evokes the "fire" or "life" in a brilliant; Scintillation
brilliance - the "sparkle" of the stone when moved, caused
by light reflections of the light source.
- Dodson's definition (1978): A measure of the light that,
entering the crown of the stone, is scattered out of the
crown facets.
- "Professional Jeweler" (July 1998) Light Return/Brilliance.
The amount of light returned to the eye, or brilliance,
depends on how well the diamond in question reflects and
refracts light. This includes dispersed wavelengths, which
are reflected from the internal surfaces of a diamond and
returned to the eye.
- http://www.pricescope.com: Brilliance is the most important feature of a beautiful diamond. At the simplest level, brilliance is reduced if light leaks out the back of a diamond. In a more complex analysis, the direction that light enters and leaves the top of a diamond becomes very important. A very deep pavilion diamond returns light straight back to the viewer, so in fact when you look face onto the table your head blocks the light and the diamond looks dull. Some diamonds that are too shallow suffer a similar problem (with a different cause).
2. Discussion
It is well know in gemology and trade that the diamond appearance is described in terms of Brilliance, Scintillation and Fire. These three parts describe the diamond appearance completely.
Literature review and comparison of trade opinions show that the "Brilliance" term is not clearly defined and there is no one generally accepted definition.
Probably about 50 years ago the word "Brilliance" was used as ultimate description of the diamond appearance. At that time it was a synonymous with "Beauty". Evolution of ideas was leaded to separation of "Fire" as a characteristic of colored part of Brilliance and after that to separation of "Scintillation" what characterized a moving diamond. All that remained after separation of these two properties is known today as "Brilliance".
At present time there are three different ideas of brilliance:
I. Diamond beauty (as 50 years ago);
II. Diamond beauty minus Scintillation minus Fire;
III. Light Return (sometimes including external luster or sometimes taking into account internal reflections only).
3. Here we are posting two following
definitions of "Brilliance" for your suggestions
First definition.
Brilliance is the characteristic of a diamond, which remains when we "take" all its appearance and "subtract" Scintillation and Fire. The human eye will see Brilliance as combination of white, gray and black zones for motionless diamond ( i.e. colored zones are eliminated).
Second definition.
The phenomenon called Brilliance consists of two parts. The first one is based on comprehension of primary/initial/incipient brightness and contrast of diamond image (motionless photo-shots taken from different positions). The second part consists of posterior/subsequent traditional comprehension of some phenomena as negative or positive (like «Fish-Eye», «Nail Head», «Leakage», thick girdle, symmetry deviations, Tolkovsky pattern, «Ideal Cut»).
This second part appeared due to attempts to grade the first part of Brilliance and to interpret it by viewing many diamonds. And nowadays the members of the contemporary market have in their memory a set of standard images, which people have already associated with positive or negative emotions.
Perhaps to evaluate Brilliance objectively the first part would be well enough, but it would not be enough for a human subjective evaluation because a human mind could hardly grade/calibrate it. It is easier for a human brain to grade/evaluate Fire of Scintillation because under fixed illumination conditions one can easily count "two flashes" or "four bright sparkles during motion" or "no one colored facet". Seemingly the attempt to replace "Brilliance" by "Light Return" is bound up with the very need to grade.
Comprehension of the first part of Brilliance depends on sex and age of people. Comprehension of the second part of Brilliance depends on the environment/culture where people grow. As a consequence the comprehension of the second part of Brilliance will vary for different nations, times, social groups, etc. This phenomenon is similar to tastes (like preferences of types of clothes, vine, women, men, cars, books .... etc).
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