GÜBELIN - GEM LAB - Diamond Reports

This is the identification number of your report. It allows us to determine when and where your item was examined. It is also a means of establishing whether or not the report is authentic. When communicating with us on an existing report, we need this number to track down its details.

This usually corresponds to the date of the analysis. In the case of a duplicate report, this date reflects when it was issued, not the date of testing.

In order to ascertain the exact weight of a gemstone or item of jewellery, we use a highly accurate scale. The unit of measurement used for the weight of a gemstone is a carat. One carat is equal to one fifth of a gram, i.e. 0.2 grams. The measurement in carats is given to two decimal places.

The cut of a diamond describes its shape and style:

 

Shape: diamonds are most commonly cut into round, oval, octagonal and heart shapes. There is a wide variety of standard shapes, each of which may also be modified to the extent that they can become fancy shapes.

 

Style: the style describes the cut. For example, the term “brilliant cut”, the most common diamond cut, consists of 58 facets – 33 on the crown (above the girdle) and 25 on the pavilion (below the girdle).

A micrometer is used to measure accurately the dimensions of a diamond. The measurement unit we use is millimetres; each measurement is given to two decimal places.

Depth: the depth of a stone measured from the table to the culet. It is expressed as a percentage of the stone’s diameter at the girdle.

 

Table: the size of the table of a fashioned diamond is expressed as a percentage of the stone’s narrow-girdle diameter. On a round brilliant diamond, it is measured from corner to opposite corner, rather than from flat side to flat side.

The girdle is the fine belt around the middle of the diamond. It may be polished, bruted or faceted, and can vary in thickness.

The culet is the size of the point at the bottom of the diamond. It varies from ‘none’, meaning razor sharp, to ‘very large’, meaning the point is very flat.

The term ‘polish’ refers to the presence of polishing lines that appear on the surface of a finished diamond with the use of 10x magnification. Polish is graded on a scale from excellent to poor.

The term ‘symmetry’ considers the evenness of a diamond’s outline and the size, shape and placement of its facets with the use of 10x magnification. Symmetry is graded on a scale from excellent to poor.

The clarity grade describes the number of inclusions within a diamond. ‘Internally flawless’, for example, is used to describe a diamond in which no internal features can be recognised at 10x magnification. The following clarity grades are used:

FL	flawless
IF	internally flawless
VVS 1 - VVS 2	very, very small inclusions
VS 1 - VS 2	very small inclusions
SI 1 – SI 2	small inclusions
I 1	small inclusions visible to the trained eye
I 2 – I 3	small inclusions visible to the naked eye

Diamond reports have an idealised line drawing of the diamond on which symbols are used to indicate the position, size, shape and nature of significant clarity characteristics (e.g. inclusions).

To the naked eye, most diamonds appear colourless. An expert, however, can distinguish the minimal nuances of colour that determine the value of a stone. ‘D’ is used to describe the most excellent white of a colourless diamond. Moving down the alphabet from D, each letter describes the near colourlessness to light yellowness of the stone.

D		exceptional white +
E	colourless	exceptional white	river
F		rare white +
G		rare white	top wesselton
H	near colourless	white	wesselton
I		slightly tinted white	top crystal
J		slightly tinted white	crystal
K	faint yellow	tinted white
L		tinted white	top cape
M - R	very light yellow	M tinted to R tinted	cape
S - Z	light yellow	S tinted to Z tinted

Diamonds are best known in their clear, colourless state. However, diamonds also exist in colours. The variety of shades is impressive, ranging as it does from yellow, brown, blue, purple, pink, red and green to black. The intensity of colour, i.e. the saturation of coloured diamonds, is usually lower than in coloured gemstones. These ‘fancy coloured’ diamonds are tremendously precious and highly prized. Their colours are due, amongst other things, to minute quantities of chemical elements such as nitrogen, boron and hydrogen that enter the diamond structure by replacing some carbon atoms. Atomic vacancies are another reason for colours in diamonds.

Some diamonds will fluoresce under ultraviolet light, i.e. emit a light activated by UV radiation. This is one characteristic which helps identify an authentic diamond. The strength of fluorescence ranges from weak, faint, moderate, strong to very strong. The fluorescence colour can be blue, white, red or yellow.

This is where we report on whether the colour of a fancy colour diamond is natural or treated. The appending of an Appendix or Note page is usually mentioned in the Comments section.

Each of our fancy coloured diamond reports comes with a photograph taken by our photographer in the laboratory. The high-resolution photos are true to scale and approximately true to colour.