Analysis & grading

How GIA identifies coloured stones

GIA receives a varied and complex range of items for identification; everything from coloured stones and pearls, unusual carvings and jewellery, to the latest in synthetics and simulants, as well as treated gems. A significant area of activity involves the origin of colour in gemstones, most notably, but far from limited to, diamonds, rubies and sapphires.

Inspection, care and handling procedures

GIA applies the same item identification and tracking procedures to gem identification as it does to diamond grading. Each item is assigned a bar-coded label with a unique internal identification number that is used to track it throughout the process. And at every step, special inspection, care and handling procedures serve to protect a gem’s identity and ensure that it is managed with the utmost care.

Weights and measures

This is the first stop for any gemstone. Loose gems are weighed using an electronic micro-balance that captures the weight to the fifth decimal place. Loose polished stones are also measured with an optical measuring device to determine their proportions, measurements and facet angles. Mounted stones are measured, but not weighed.


Items are then transferred to the Identification Inventory Control department for distribution to trained and experienced gemmologists for servicing. Once an item has been received by an initial gemmologist, its recorded weight and measurements are verified, or if the item is mounted or strung, the gemmologist will use manual measuring devices to determine and record the necessary measurements.
Employing state-of-the-art technology in their research and identification efforts, the gemmologist then performs a variety of analytical investigations, including a microscopic examination of the item, and performs all of the tests required to properly determine its gemmological identity and detect any treatments.
After that, the item is transferred to a second gemmologist, who independently repeats all the necessary observations and testing. Depending on the identity and nature of the item, it may be examined by additional gemmologists and research specialists.

Report processing and item return

Reports are generated after all results are finalised and services have been completed. All GIA Reports are examined and proofread to ensure quality before being sent to the client.
Lastly, the item is placed in its original container, joined by its report, and goes through final inspection and testing to ensure that the same submitted item is returned to the client.
Items are returned either in person through the Client Services department or via courier through the Transport Services department. All information recorded for an item remains stored in the GIA laboratory’s permanent database for future reference.