GUBELIN - GEM LAB - Coloured Stone 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.

This describes the actual condition of the gemstone, e.g. if it is faceted, polished, carved or rough.

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.

Gemstones are most commonly cut into round, oval, cushion, pear, 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.

The style describes the way in which a gemstone has been cut or polished.

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

Transparency describes the amount of light able to pass through the gemstone. We use the following terms to describe the different grades of transparency:

• Transparent: the stone is completely transparent – you can see all the way through and can read a text through it.
• Semi-transparent: there is slight haze in the stone, you cannot see clearly through. Reading text through the stone is almost impossible.
• Translucent: some light passes through the stone, but it is difficult to see through it.
• Semi-translucent: a tiny amount of light passes through the stone.
• Opaque: no light manages to pass through the stone at all.

Gemstones come in all shades of the rainbow. People often associate the name of a gemstone with a particular colour, i.e. sapphire equals blue. It is important to point out that this is not always the case. A sapphire, for example, may be yellow, orange or pink. Trade colours not only describe a gem’s particular hue but also imply a certain quality, such as transparency, size or the presence or absence of treatments.

The terms ‘species’ and ‘variety’ are based on the taxonomy established by mineralogists. However, gemmological practice might have slightly altered the original definitions and uses. Minerals with the same structure and general chemical composition belong to the same species. For example, ruby and sapphire belong to the corundum species.

Varieties are types of gems which belong to the same species but which exhibit a different colour, typically due to the presence of small amounts of trace elements. For example, ruby is the red variety of corundum due to the replacement of small quantities of aluminium atoms by chromium and/or vanadium.

On request, the Gubelin Gem Lab can express an opinion on the probable geographic origin of a gemstone. This opinion is based on comparisons of the stone’s internal characteristics and physical and chemical properties with the characteristics of reference stones from a known origin. It is not always possible to determine an origin; in some cases, the available information is insufficient or ambiguous, in which event we do not comment on the origin.

This is where we report on whether and how a gemstone is treated, or if the colour is natural.

The appending of an Appendix or Note page is usually mentioned in the Comments section.

Each of our Gemstone 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