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Determination
of the cut quality of a diamond and visual evaluation of its beauty
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The factors
that determine the cut quality of a diamond and the visual evaluation
of its appearance can be divided into three main groups: |
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1.
Parameters of light sources that characterize the illumination of
the diamond: |
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Source
type (its radiation spectrum, luminance, and angular size) |
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Source
position |
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The
number of such sources. |
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2. Optical
effects exhibited by the diamond itself and its optical properties:
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Light return - the
capability of the diamond to return a fraction of the incident
light to the observer's eye |
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Fire - the capability
of the diamond to disperse a white light into iridescent colors
perceived by the observer |
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Color - the result
of the dependence of the light absorption factor of the gem
upon the wavelength of the incident light |
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The pattern of facets and highlights within the
diamond and their symmetry |
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"Dynamic Contrast"
- the rate of change of the diamond appearance while it is rotated
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Clarity - the preferable
absence of internal inhomogeneities that absorb or scatter light
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The flatness of the facets, the quality of their
polishing, and the surface smoothness |
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3. Viewing
conditions: |
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The
observer's position with respect to the diamond |
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The
psychophysiological features of the observer: |
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vision stereoscopy |
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pupil motion |
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color perception, effect of background |
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eye's resolution |
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eye's sensitivity |
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spatial and temporal (the difference in successive
views of the gem) contrast |
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The
psychological criteria for evaluating the diamond beauty.
The existing stereotypes and the fashion of the market. |
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The correlations
between some of the above factors are given below: |
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Diamonds cut similarly but having not equal size
are perceived quite differently. Smaller diamonds are usually
cut so that to have fewer facets. The influence of the size
of a gem upon its fire is most strong. |
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The radiation spectrum of the illumination source
determines the perceived color of a diamond and affects its
fire as well. The color depends on the product of the radiation
spectrum of the source by the transmission spectrum of the gem.
Both multipliers are equally important. The coloration of the
diamond, as a rule, weakens its fire. In some cases, intensive
coloration may completely eliminate the fire. |
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The angular size of the illumination source strongly
affects the fire of the diamond; |
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The positions of multiple illumination sources
and their total number determine the " Dynamic contrast" and
the pattern of highlights. |
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Poor polishing reduces both fire and light return
of a diamond; |
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So do internal defects of the gem; |
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A snapshot of a diamond is not adequate to its
image visually perceived by an observer; |
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The cut of a diamond should be evaluated under
those illumination conditions being peculiar to the place where
it is used "); |
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Traders are prejudiced against non-typical cut
parameters and facet patterns; |
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The degree of symmetry of a diamond strongly
affects its beauty. |
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It is inadmissible to improve the appearance
of a diamond (as evaluated by an observer) by considerably decreasing
its weight; |
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For the evaluation of the cut quality of a colorless
or weakly colored gem, its light return is not so important
as the fire and " Dynamic contrast ". |
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The
authors of the project:
Sergey Sivovolenko,
OctoNus
Software, model and calculations
Yurii Shelementiev,
Gemology
Center of MSU, gemology
Anton Vasiliev,
"LAL" company, optics
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