In the vocabulary of cut grading, digging out — sometimes called dug-out facets — describes a faceting defect in which the pavilion facets of a faceted gemstone have been cut at angles steeper than the optical ideal, causing those facets to meet the girdle plane at abnormally acute junctions. Viewed through the table, the effect manifests as dark, hollow-looking zones that interrupt the stone's brilliance pattern. The term is in regular use in trade discussions, cut-grading reports, and gemmological education, and it represents one of the two principal pavilion-angle errors in faceted stones — the other being painting, in which pavilion facets are cut too shallowly. Understanding digging out is essential for buyers, appraisers, and cutters alike, because the defect has direct consequences for optical performance and, when correction is attempted, for finished weight.

Geometry of the Defect

Every faceted gemstone relies on a carefully calibrated relationship between the refractive index of the gem material and the angles at which its facets are cut. For a standard round brilliant in diamond, the pavilion main facets are conventionally cut at approximately 40.75° to 41.0° relative to the girdle plane; for coloured stones, the optimal angle varies with the material's refractive index — higher-RI stones such as demantoid garnet or zircon tolerate steeper angles before total internal reflection breaks down, while lower-RI stones such as quartz require shallower pavilion angles to achieve the same effect.

When a cutter sets the pavilion angle too steep — whether through miscalibration of the faceting machine, an attempt to retain rough weight, or simple error — the pavilion facets angle inward more sharply than the geometry of total internal reflection requires. Light entering through the crown strikes these over-steep facets at angles that exceed the critical angle for the material and passes through the pavilion rather than being reflected back toward the observer. The result is localised light leakage through the base of the stone, visible to the eye as dark or hollow patches when the stone is viewed face-up. In coloured stones, these zones may appear as windows of reduced saturation or, in strongly pleochroic materials, as patches showing the wrong pleochroic colour.

The term "digging out" is visually apt: the steep junctions at the girdle give the impression that material has been scooped or gouged away from the stone's profile, leaving angular recesses rather than the smooth, flowing silhouette of a well-proportioned pavilion.

Causes in Practice

Digging out arises from several distinct pressures and errors in the cutting process:

• Weight retention from the rough. A cutter working with expensive rough — particularly fine ruby, emerald, or alexandrite — faces commercial pressure to preserve as many carats as possible. Steepening the pavilion can allow a larger finished diameter, or can avoid cutting through an inclusion-free zone, at the cost of optical performance.
• Accommodating crystal habit. Many gem crystals have natural terminations, cleavage planes, or growth features that make a steep pavilion the path of least resistance. Cutters working rapidly through commercial parcels may follow the crystal rather than the ideal angle.
• Machine miscalibration or operator error. On a mechanical faceting machine, an incorrectly set angle index or a slipping quill can introduce systematic errors across an entire cutting session.
• Correcting an earlier defect. A cutter attempting to remove a chip or abrasion from the pavilion of an already-finished stone may inadvertently steepen the surrounding facets in the process.

Visual Identification

Identifying digging out does not require specialised equipment, though a proportion scope or digital imaging system makes the diagnosis unambiguous. The principal face-up indicator is a pattern of dark, angular zones radiating from or near the culet, often described in trade parlance as a "nail-head" effect when the digging out is severe and centred. Unlike the broad, pale window that characterises painting, the dark zones of digging out tend to be sharper-edged and more angular, reflecting the geometry of the over-steep facet junctions.

Viewed from the side, the pavilion of a dug-out stone will appear noticeably deeper relative to its diameter than a well-cut stone of the same species. A simple depth-to-diameter ratio measurement — readily obtained with a digital calliper — will confirm an abnormally high pavilion depth percentage. In round brilliants, a pavilion depth consistently above approximately 44–45% of the girdle diameter is a reliable indicator that digging out may be present, though the precise threshold varies by material.

Cut-grading reports from major gemmological laboratories, including those issued by the Gemological Institute of America, evaluate pavilion angle as a component of overall cut grade. A stone flagged for an excessively steep pavilion angle in the proportions section of such a report should be examined face-up for the characteristic dark zones before purchase.

Optical Consequences

The primary consequence of digging out is reduced brilliance — the proportion of incident white light returned to the observer's eye. Because the over-steep pavilion facets fail to achieve total internal reflection, light that should have been recycled within the stone and returned through the crown is instead lost through the base. In transparent coloured stones, this loss of internal light return also diminishes the depth and evenness of colour saturation, since colour in a faceted gem is partly a function of the path length light travels through the body of the stone before reaching the eye. A dug-out stone may appear paler or less vivid than a well-cut stone of identical chemistry and colour concentration.

In strongly coloured material — deeply saturated Thai or Mozambique ruby, for instance — digging out may paradoxically produce a stone that appears slightly lighter and more transparent face-up than its body colour would suggest, because the dark zones interrupt the colour saturation that a fully brilliant stone would display. This can mislead a buyer into thinking the colour is cleaner or lighter than it truly is.

Relationship to Painting

Digging out and painting occupy opposite ends of the pavilion-angle spectrum and produce superficially different but equally undesirable optical results. A painted stone — one with pavilion facets cut too shallowly — displays a broad, pale, washed-out window through the table, through which the reflection of the observer's hand or the surface beneath the stone is clearly visible. A dug-out stone, by contrast, displays dark angular zones rather than a pale window, and its profile appears deep rather than flat. In trade usage, both defects are described as failures of make — the cutter's craft — and both reduce a stone's desirability and value relative to a well-proportioned equivalent.

It is possible, though uncommon, for a stone to exhibit elements of both defects simultaneously if different facet groups have been cut at inconsistent angles — a sign of particularly careless or rushed cutting.

Remediation and Weight Loss

Correcting digging out requires recutting the pavilion: the over-steep facets must be reground and repolished at the correct angle for the material. This is a straightforward operation for an experienced lapidary but carries an unavoidable cost in finished weight, since material must be removed from the pavilion to bring the facets back to the proper angle. The weight loss depends on the severity of the original error and the size of the stone; in commercial-grade material, the loss may be acceptable, but in fine, large stones — where each point of carat weight carries significant value — the decision to recut must be weighed carefully against the improvement in optical performance and the resulting per-carat premium a well-cut stone commands.

In some cases, particularly with expensive rough that was dug out precisely to preserve weight, the economics of recutting are unfavourable, and the stone remains in trade in its defective state, often at a discount that experienced buyers recognise but casual purchasers may not.

In the Trade

Awareness of digging out is particularly important when purchasing coloured stones in parcel lots from cutting centres in Jaipur, Bangkok, or Guangzhou, where high-volume commercial cutting prioritises yield over optical performance. Buyers working at the wholesale level routinely cull dug-out stones from parcels before resale, accepting the reduced count in exchange for a more consistent make. At the retail and auction level, cut quality has become an increasingly explicit criterion for fine coloured stones, and a well-documented, well-cut stone commands a meaningful premium over an equivalent stone of poor make — a premium that the cost of recutting a dug-out stone can, in favourable cases, justify.