Post-mounting Report — Gemmological Documentation on a Set Stone
Post-mounting Report — Gemmological Documentation on a Set Stone
What the major laboratories can determine on a stone in its mounting and what they cannot
A post-mounting report is a gemmological document issued for a stone that remains set in its jewellery rather than removed for examination. The major laboratories — including GIA, Gübelin, SSEF, AGL, and AGS — issue post-mounting reports on request, with the document scope reflecting the limitations the mounting imposes on observation. Post-mounting reports are commonly commissioned for high-value stones where removal from the setting is impractical, where the mounting is itself of historical or design value, or where the client wishes to document the stone without disturbing the piece.
What a post-mounting report contains
A post-mounting report typically includes species and variety identification, colour description, treatment determination, and a clarity description based on what is observable through the mounting. The report identifies the stone as set in jewellery, describes the visible portion of the stone (table, crown, and as much of the pavilion and girdle as the mounting permits), and provides the laboratory's opinion on treatment status to the extent the analytical work supports it.
For a corundum mounted in a closed-back setting, for example, the laboratory can typically read body colour, identify the species, run ultraviolet-visible-near-infrared spectroscopy through the table to detect heat-treatment markers, and provide treatment commentary; it cannot weigh the stone, measure its dimensions accurately, or evaluate inclusions in the pavilion. For a diamond in a prong setting with most of the girdle visible, the laboratory can typically estimate weight from measurements taken through the prongs and provide a clarity grade with the mounting limitation noted, though the precision of these estimates is lower than for an unmounted stone.
What the report cannot include
The principal limitations of a post-mounting report are the inability to weigh the stone directly, the inability to measure all dimensions precisely, and the restricted observation of inclusions and surface features. The laboratory typically reports estimated dimensions and weight rather than measured values, and notes the estimation explicitly on the document. Origin determination, which depends in part on inclusion observation across the full stone volume, is more difficult to support on a mounted stone and may be qualified or omitted on the post-mounting document.
When to use a post-mounting report
Post-mounting reports are appropriate in several circumstances. High-value antique and signed jewellery loses value if the stone is removed from its original setting, so post-mounting documentation preserves the piece's integrity while still providing laboratory commentary. Insurance documentation and estate appraisal often work from post-mounting reports as a standard procedure. Stones in mountings that would be destroyed by removal (rivière necklaces with closed-back collets, certain Edwardian and Art Deco platinum work) are routinely documented post-mounting.
Pre-mounting reports — issued for unmounted stones — provide more complete documentation and are appropriate when the stone is being purchased loose or when the mounting work has not yet been done. The pre-mounting report can later be cross-referenced against a post-mounting examination to confirm the same stone, providing a chain-of-identity document for the piece.
Laboratory practice
Major laboratories maintain specific protocols for post-mounting work, including the photographic documentation of the mounted piece, the description of the mounting itself in summary terms, and the explicit notation of all measurements and weights as estimated rather than measured. The report's wording is conservative on points where the mounting limits the laboratory's confidence, and the document is clear about the scope of its conclusions.
In the trade
For dealers and clients, post-mounting reports support transactions on antique, signed, and high-value mounted pieces without requiring de-mounting. The reports are accepted as valid laboratory documentation for insurance, estate, and resale purposes, with the post-mounting context understood by the trade. The cost of a post-mounting report is generally comparable to that of a pre-mounting report at the same laboratory, with the practical limitation being reduced laboratory throughput on mounted work compared with unmounted parcels.