Pinpoint Cloud — The Hazy Inclusion Feature
Pinpoint Cloud — The Hazy Inclusion Feature
A cluster of pinpoint inclusions dense enough to read as faint haze under magnification
A pinpoint cloud is a cluster of pinpoint inclusions in a diamond or coloured gemstone, dense enough to register as a faint, hazy area under 10x magnification when individual pinpoints would not separately be visible. Pinpoint clouds are common in diamonds and represent one of the principal mechanisms by which clarity grades fall from Very Slightly Included (VS) into Slightly Included (SI) in otherwise clean stones. The trade convention is that pinpoint clouds are reported as cloud on laboratory grading reports, often with the comment cloud not shown indicating that individual pinpoints are too small to plot but collectively affect appearance.
Composition and origin
Pinpoint clouds in natural diamonds are formed during diamond growth in the deep mantle, when fluid or solid micro-inclusions become trapped along growth fronts and cluster into spatially associated groups. The individual pinpoints within a cloud are the same minute crystal phases that form isolated pinpoints — olivine, garnet, sulphide, and other accessory minerals — but their spatial association produces a different optical effect at the cloud-density level than at the isolated-pinpoint level.
Pinpoint clouds in synthetic diamonds carry diagnostic significance. CVD synthetic diamonds frequently display pinpoint clouds aligned along growth layers, producing striated or sheet-like cloud features that can be recognised under crossed polarisers as oriented along the {100} growth surfaces of the synthetic crystal. HPHT synthetic diamonds may contain metallic flux pinpoint clouds with characteristic compositions and distributions. The recognition of these oriented cloud structures is a principal diagnostic technique in laboratory determination of synthetic origin.
In clarity grading
Pinpoint clouds in natural diamonds may be the grade-setting feature in stones graded at VS2 (a localised cloud not affecting transparency), SI1 (a more extensive cloud noticeable under magnification), or SI2 (a substantial cloud reducing transparency or producing a hazy appearance face-up). Stones graded at I1 (Included) for cloud-only inclusion suites are generally those in which the cloud reduces face-up transparency or brightness.
The GIA reporting convention for pinpoint clouds includes the descriptive note cloud is not shown when individual cloud constituents are too small to plot as separate symbols. The note appears with the cloud's general location on the clarity diagram and indicates that the cloud is present and grade-setting without committing to a specific plotted extent. The convention applies to coloured-stone laboratory reports as well.
Visual effects
The visual effect of a pinpoint cloud depends on the cloud's density, location, and extent. Light-density clouds in well-positioned locations may be invisible to the naked eye and produce only a faint haze under magnification. High-density clouds, particularly those covering a substantial proportion of the table or extending into the pavilion, can produce a visible reduction in transparency and a milky or hazy face-up appearance. The most extreme cases are the so-called milky diamonds, in which pinpoint cloud density is sufficient to dominate the stone's optical character.
For coloured gemstones, pinpoint clouds may also scatter light and reduce brilliance, particularly in stones whose colour saturation is critical to value. Pinpoint clouds in fine sapphires and rubies are generally considered acceptable when small and well-positioned but are read negatively when extensive enough to affect face-up colour or transparency.
In the trade
The trade convention for buyers of diamonds with pinpoint cloud inclusions is to evaluate the cloud's visual impact face-up under standard viewing conditions rather than relying solely on the laboratory clarity grade. Two stones at the same SI1 grade may differ substantially in their face-up appearance depending on whether the cloud is concentrated in a locally bounded zone or distributed across the table; the bounded-cloud stone is generally preferable. The trade-press term milky SI describes the unfavourable case of an extensive cloud producing visible haze.
For coloured gemstones, similar evaluation principles apply. Cloud features in sapphires and rubies are read in conjunction with origin determination and treatment status to produce a complete picture of stone quality.