Jager (also spelt Jaeger in older British and Continental literature, and Jäger in German) is a historical trade designation for the highest colour grade of natural diamond rough, used in the South African and London diamond trade from the late nineteenth century through to the introduction of the GIA D-to-Z grading scale in the 1950s. The term denotes a stone of the most colourless quality, with a faint blue tint visible in transmitted light, and corresponds approximately to D and E colour in the modern GIA scale.

Origin of the name

The designation derives from the Jagersfontein mine in the Orange Free State, opened in 1870 by the Visser family on the farm of Jacobus Jagers and acquired in 1891 by the New Jagersfontein Mining and Exploration Company. The Jagersfontein mine was, throughout its productive life from 1870 to 1971, recognised as the source of the most consistently colourless and finest-coloured diamond rough in the world; "Jagersfontein" or simply "Jager" became the trade shorthand for that quality grade regardless of the actual mine of origin.

The classical colour grades

The pre-GIA trade recognised a sequence of colour grades, each named after a reference mine: Jager (highest, slight blue cast, modern D-E), River (very white, slight blue, modern E-F), Top Wesselton (very white, modern F-G), Wesselton (white, modern G-H), Top Crystal (slightly tinted, modern H-I), Crystal (faint yellow, modern I-J), Top Cape (modern K-L), Cape (modern M-N), and Yellow Cape (modern O-P and below). The system was in use through the South African and London trade from approximately the 1880s and continued in some markets, particularly Antwerp and the European trade, well into the 1970s. The German trade and the older Indian wholesale market still occasionally use Jager, River and Wesselton informally for stones of the corresponding GIA grades.

The Jagersfontein mine

The Jagersfontein mine produced several of the best-known diamonds in history, including the Excelsior Diamond (995.20 carats rough, 1893), the Jubilee Diamond (650.80 carats rough, 1895), the Reitz Diamond (later renamed the Jubilee), and a long sequence of fine large blue-white stones throughout its productive life. The mine was a unique kimberlite pipe in producing such consistent high colour, and the geological reason — generally attributed to a relatively short residence time at high pressure and to nitrogen-aggregation history — has been the subject of repeated GIA Gems & Gemology technical work.

Modern usage

The term is now largely historical, replaced in trade and laboratory work by the GIA D-to-Z scale and equivalent CIBJO and HRD grades. Older auction-house catalogues, estate-jewellery descriptions and continental European gem appraisals still occasionally use Jager, particularly for diamonds with strong pre-1960 provenance. From a buyer's perspective, a description of an antique stone as "Jager colour" should be read as a claim of D or E colour and should be confirmed by laboratory grading before commercial reliance.