New kid on the grading block

Once the Argyle mine came into production in the mid-1980s, however, this all changed, with a significant influx of small brown diamonds entering the supply chain. The extraction cost of these stones was in the ballpark of $7 US per carat compared to $170 US per carat for rough that would later come out of Canada’s Ekati mine. This injection of cheap raw material and the growing low-cost labour force in India’s diamond cutting centres created an explosion of brown diamonds that could reach a much wider retail audience.

Initially, there was no clear cut direction as to how to colour grade these stones, given they did not fit any of the historical ‘white to yellow’ grading scales in use at the time. As brown diamonds became more and more prevalent in the marketplace, however, the trade developed a grading scale based on the one used for Cape coloured diamonds (Figure 2).

Even though these two scales shared the same prefix in the terminology used to describe the stone’s colour (i.e. TTL, TL, and L before C or B), there was no real equivalency in the actual intensity. However, there is one key thing that holds true throughout the diamond trade: stones from the Cape series are more sought-after and more expensive than brown diamonds with similar intensity.

This difference in price is due to more than Cape diamonds simply having a longer history compared to browns; it all comes down to the stone’s overall look. One of the key factors justifying the difference in price boils down to blue fluorescence—those in the Cape series that fluoresce appear whiter, as opposed to brown stones with the same intensity of colour, which show no apparent change. As well, once set in jewellery, the TTLC to LC diamonds exhibit a warmer appearance than their counterparts in the brown colour range, which are almost grey. As such, experienced buyers look to purchase Cape series diamonds at the price of browns.