1.7% in the cheap colours: what July's flat month hid

§1The shape inside a flat month.

A flat month has a shape inside it. This paper led on 4 August with the RapNet Diamond Index for one-carat polished unchanged across July, closing a slide that had run without a positive print since June 2025. Rapaport's Diamond Pulse for August now breaks that same month open by colour, and the flat line turns out to be an average of two different markets. One-carat goods in D to F and G to J colour, in IF to VVS and VS clarity, averaged a gain of 0.1% in July. K to M colours averaged 1.7%. K to M in VS swung from a 0.1% loss to a 2.8% gain.

A flat index is an average, and averages hide the thing that moved. On the newsletter's own figures the cheapest colour band ran seventeen times the gain of the better bands last month, this desk's division of 1.7 by 0.1, which is the sort of ratio that only survives while the numerator is small. The point is not the multiple. The point is that the recovery this paper has been describing since 14 July as a bottom-up move now has a second dimension. It was already running from the bottom of the size chart: in the same July, 0.30-carat goods gained 1.6% and 0.50-carat goods 1.8% against a flat one-carat, figures this paper published on 4 August. It is now also running from the bottom of the colour scale.

§2Bottom-up in two dimensions now.

That fits what the trade has been buying rather than what it has been saying. The goods moving are the goods a cautious retailer reorders, and a K to M stone at VS clarity is exactly the compromise a buyer makes when the budget is fixed and the carat weight is not negotiable. It also means the headline number a jeweller quotes as evidence of a turn is the one number in the set that did not turn. The one-carat index was flat because a near-flat top and a rising bottom cancelled inside it, and anyone reading the single figure took away the opposite of what the components say.

§3One source, and it owns the index.

The limits of this should be stated. It is one source, and that source is the owner of the index reporting on its own index, which makes it primary and interested at the same time; there is no second publisher of RapNet colour-band moves to check it against. The rest of the August newsletter is material this paper has already run and re-checked rather than new: global rough production down 8% to 98.8 million carats in 2025 ran here on 27 July, De Beers' first-half revenue down 19% to $1.58 billion ran here on 31 July, and the Section 301 bands of 10% and 12.5% on jewellery and gemstone imports ran here on 25 July. The colour split is the one line in it this paper had not published.