Diamond certificates have become an essential
part of the diamond trade. Originally, diamond certificates were mainly
required by professionals, but in recent years consumer demand is growing
steadily too.
After all, buying a diamond is something special. Each diamond has its own
personality; it is a unique work of art, made partially by nature and by
human hand. To fully appreciate a stone, information is needed and this
can be found in a diamond certificate. A certificate is of course only
useful if it is reliable. The HRD certificate enjoys an excellent
reputation for objectivity and quality. The objectivity of the grading
results is guaranteed by preserving the strictest anonymity. When a
diamond is brought in for examination at the reception of the Certificates
Department, all data are introduced into the computer. The stone then
receives two numbers: an external number for use of the client, which is
printed on the receipt note, and an internal number to follow the stone in
the lab. The graders who perform the examination never know to whom a
stone belongs, which is a guarantee for absolute objectivity. Where
quality is concerned, all possible efforts are made. The main factor in
grading a diamond remains the diamond expert, in other words the grader.
The HRD Certificates Department pays much attention to training new
graders: only after six months of intensive theoretical and practical
training a new employee is actually integrated in the certification
process.
Each diamond is examined by several graders, so that the opinion of the
less practised persons can be compared to that of experts with years of
experience. In this way, the grading results mentioned in the certificate
always reflect the judgement of several graders, thus ensuring a high
level of reliability.
The laboratory where the examinations take place is equipped with very
sophisticated machinery, such as spectrophotometers, Dia-Mension systems,
cathode luminescence apparatus, The graders all work with a special
diamond microscope. Originally, the HRD Certificates Department mainly
designed and manufactured microscopes for its own use, starting from its
extensive practical know-how in diamond grading. Today, the microscopes
are also increasingly in demand on the market. The HRD microscopes,
standard equipped with built-in illumination and an ingenious gem
manipulator with vacuum system, are very valuable tools in diamond
grading.
A diamond certificate first of all guarantees the authenticity of the
diamond. In other words: the document confirms that the stone described is
indeed a natural diamond, and for example not an imitation or a synthetic
material. Therefore, the authenticity is the first thing to be checked in
the lab. There are various methods of testing a diamond, based on its
particular characteristics such as hardness, light refraction and heat
conductivity.
The certificate furthermore contains a complete quality description of the
diamond. These quality characteristics determine the value of the stone.
Subsequently, the certificate mentions: shape, weight, clarity grade,
fluorescence, colour grade, measurements, proportions and finish grade,
possibly supplemented with comments.
The certificate is routinely drawn up in English, since it is the English
terminology that is most widely used in diamond circles. For this reason,
it has been decided not to issue "translated" certificates.
The main quality characteristics are referred to as the 4 Cs:
Carat (weight), Clarity, Colour and Cut.
The clarity or purity of a diamond is determined by the number, the
size, the brightness and the location of the internal and external
characteristics, important structure phenomena and transparency.
Generally speaking, mainly the inclusions - the impurities inside the
stone - are important for the clarity grade. External characteristics on
the surface of the stone only have an influence on the clarity grade if
they are sufficiently noticeable and if the stone is already internally
flawed. The stone is examined with a loupe and a microscope, during which
all characteristics having a bearing on the clarity are noted down. Each
stone is examined by several graders, and only if enough opinions are
identical the final grade is decided on. The best clarity grade is called
loupe clean", literally meaning "clean when viewed through a
loupe". According to the IDC Rules, a diamond is loupe clean if,
after an examination by an experienced grader with a loupe 10x (corrected
for spherical and chromatic aberration), under standardised light
conditions, it has been found free of internal characteristics. If the
stone has no internal and no external characteristics distinguishable with
the loupe 10x, it is called loupe clean without further comments.
If there are no internal characteristics but external ones can be seen,
these are mentioned under Identification Marks" or
"Comments", depending on how important they are. Loupe clean is
followed by the clarity grades vvs1/vvs2, which stand for very very small
characteristics, very hard to find with the loupe.
The next grades, in descending order, are vs 1 /vs2 (very small
characteristics) and si I /si2 (small inclusions). As can be noted, each
clarity grade is further subdivided into 1 and 2, depending on, again, the
number, size, brightness and location of the characteristics. In all these
clarity grades, the inclusions are very hard to easy distinguishable with
a magnifying loupe 10x. The lowest clarity grades on the scale (indicated
by P for Pique') refer to inclusions that can be seen by an experienced
grader with the naked eye. Depending on the importance of the
characteristics P1, P2 and P3 are distinguished. On the drawing on the
left page of the certificate, symbols show the main characteristics. This
drawing not only serves as an indication why the clarity grade was
awarded, it is also a means of identification. No two stones have exactly
the same inclusions.
Structure phenomena:
A diamond which appears to have no internal characteristics but only
structure phenomena, is called loupe-clean provided these structure
phenomena do not cause colour effects or internal light reflections and
are not too clearly visible. These structure phenomena are then mentioned
under Identification Marks or under Comments.
External characteristics:
When a diamond has no internal, but only external characteristics, it is
referred to as being "loupe-clean" and the external
characteristics are mentioned under Identification Marks or under Comments.
External characteristics equally or less important than internal
characteristics are not taken into account
The colour of a diamond is determined by comparing it to an
internationally approved series of masterstones. As with all examinations,
each stone is graded by several graders before a decision is taken. The
HRD lab also has sophisticated apparatus for colorimetric analysis
available, but the grading results supplied by these are supplementary.
The accuracy of the machinery is tested by comparing the results to those
of the lab personnel, but according to the IDC Rules the final grading is
based on human observation. Over 90% of gem diamonds have a basically
yellowish colour. The intensity can vary from nearly colourless to
yellowish. The colour grades are named according to the International
Colour Grading Scale.
The best colour is called "exceptional white+", the lowest
colour on the scale is called "tinted colour". Between brackets,
the colour grade is given according to an alphabetic scale ranging from D,
the best colour, to S-Z, The nuances between two contiguous colour grades
are very hard to distinguish. To determine the colour, a stone is placed
between the masterstones on a neutral white background (Spectralon ® ).
The subtle differences in colour between two adjoining colour masterstones
can only be accurately judged when the stones are seen through the
pavilion side. When looked at through the table, the differences are
practically unnoticeable. A very important aspect of colour grading is the
illumination used. In the HRD lab, standardised D65-lamps are used.
These lamps have a colour temperature of 6,500 Kelvin and meet the CIE
standard (Commission Internationale de I'Eclairage/ International
Commission on Illumination). Besides slightly yellowish, diamonds can have
different colours like orange, brown, pink, green, blue.... Diamonds with
a beautiful and rare colour are extremely valuable. Especially for these
unique stones, the HRD offers a Diamond Colour Certificate.
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The regular colours are
subdivided in several colour grades, called the "International
Colour Grading Scale" (see colour comparison table hereunder).
The colour grades are fixed by a series of masterstones, which, as a
definition, fix the lower limits of each colour grade. An
international reference- series has been composed by representatives
of the WFDB, the IDMA and CIBJO. The colour comparison to masterstones is done under standardised artificial light, equivalent to Northern daylight. It is recommended that the characteristics of the artificial light source to be used, approximate the C.I.E. -standard illuminant D65 (C.I.E. Commission Internationale de I'Eclairage 1 International Commission of Illumination). For the subdivision of the other colours we refer to the Diamond Colour Certificate |
Cut or make is the last of the 4 Cs. On the HRD certificate, two
aspects of the cut are judged separately: the finish grade and the
proportions. When examining the finish grade, attention is mainly paid to
possible symmetry-deviations and facets. A good finish grade testifies of
the workmanship of the diamond polisher.
The proportions, the relationship between the various parts of the stone,
determine the fire and brilliancy of the diamond. If the proportions are
not optimal, undesirable visual effects may occur. The main
symmetry-deviations and the proportions are first judged on the basis of
objective, measured data. For this purpose, a Dia-Mension system is used:
with the aid of a camera a large number of measurements are taken, after
which these are interpreted by a computer. The results are then checked by
comparing them to the grades given by the HRD experts on the basis of
visual examination with a loupe.
| "Cut" refers to the overall description of the proportions on the one hand and the finish of the diamond on the other hand. The proportions are determinative for the brilliancy and the fire of the diamond, while the finish represents the extent to which deviations occur from the symmetry and other characteristics of the cut. The description of the cut on a certificate is split into a separate description of the proportions and of the finish. | |||||||||||||||
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| The angle of inclination of the crown side can be deducted as shown below : | |||||||||||||||
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