PGS — Professional Gem Sciences, the Chicago Coloured-Stone Laboratory
PGS — Professional Gem Sciences, the Chicago Coloured-Stone Laboratory
An independent regional laboratory serving the American Midwest trade with identification and grading reports
Professional Gem Sciences (PGS) is an independent gemological laboratory based in Chicago, Illinois, providing identification, grading, treatment determination, and origin opinions for coloured gemstones and diamonds. PGS occupies a position in the American gemological-laboratory landscape between the major international laboratories — GIA, AGL, AGS — and smaller jeweller-affiliated and regional services. The laboratory's principal client base is the regional jewellery trade of the American Midwest and clients sending stones in from across the country who prefer a regional alternative to the major coastal laboratories.
Services and methodology
PGS issues reports on coloured stones and diamonds documenting weight, dimensions, shape and cut, transparency, species and variety identification, colour grading, treatment determination, and where supportable, origin opinion. The laboratory uses standard gemmological instrumentation — refractometer, polariscope, dichroscope, ultraviolet response, microscope — supplemented by spectroscopy (UV-Vis-NIR, FTIR, and Raman) for species confirmation and treatment detection. For diamonds, the laboratory follows the international colour and clarity grading conventions established by GIA.
The methodology for treatment determination follows the AGTA-coordinated terminology common across the principal American laboratories: none detected, heat only, heat with residues, clarity enhancement, diffusion, irradiation, and so on, with explanatory commentary appropriate to the stone type. Origin opinion is offered selectively for the species and varieties where the laboratory's data support a confident attribution; PGS, like other reputable laboratories, declines origin opinion where the data permit multiple interpretations.
For corundum specifically, the laboratory addresses the question of heat treatment and, separately, the more aggressive treatments such as beryllium diffusion and lead-glass filling that have appeared in commercial supply over the past two decades. The methodology for identifying these treatments combines microscopic examination for diagnostic features (residual flux, surface-reaching fractures filled with high-RI material, characteristic colour zoning) with spectroscopic analysis (FTIR for resin and oil residues, UV-Vis-NIR for diffusion-treated colour profiles) and elemental analysis where appropriate.
Position in the laboratory landscape
The American gemological-laboratory landscape includes a small number of internationally recognised laboratories at the top — GIA in Carlsbad and New York, AGL in New York, AGS Laboratories in Las Vegas before its 2022 transition into GIA — and a broader group of regional and specialist laboratories serving particular geographic markets or technical specialisations. PGS is among the most established of the regional American laboratories, with operating history dating to the 1970s and a consistent presence in the Chicago and Midwest jewellery trade.
For the working trade, the choice of laboratory depends on the stone, the destination market, and the buyer's preferences. International auction-bound coloured stones are typically sent to GIA, AGL, Gübelin, SSEF, or Lotus depending on species and provenance significance. Regional trade transactions, estate-jewellery valuations, and routine identification work are commonly handled by regional laboratories such as PGS, Stone Group Labs in Jefferson City, EGL USA in New York, and similar services. The cost differential between regional and international laboratories is meaningful for routine work and contributes to the established demand for regional services.
Reporting format
PGS reports are formatted to communicate clearly to working trade professionals, with the standard data fields presented in tabular form and with descriptive commentary on relevant technical findings. The reports include security features — sealed inscriptions, watermarks, and laboratory file numbers cross-referenced to the laboratory's internal database — supporting subsequent verification by parties handling the stone.
For diamonds, PGS reports follow the standard 4Cs format and include plotting of inclusion features at appropriate magnification. For coloured stones, the descriptive commentary on colour, clarity type, and treatment status is generally more extensive, reflecting the additional interpretive judgement required for coloured-stone work. Photo-documentation of inclusions and characteristic features is included where it supports the report's findings.
In the trade
For Chicago and Midwest jewellers, PGS is a routine working laboratory; for clients elsewhere, the laboratory is an established regional alternative when geographic proximity, turnaround time, or relationship preferences favour an American Midwest service. Estate jewellery, insurance appraisals, and routine retail-trade work form the bulk of the laboratory's volume; major auction-bound stones are typically sent to the international laboratories with the strongest market recognition for the relevant species. The trade's general practice is to use the laboratory whose report carries the greatest weight in the destination market: a Burmese ruby being sold at auction in Geneva will be sent to Gübelin or SSEF; the same stone in a regional retail transaction in the United States may be perfectly well served by a PGS or AGL report.
For valuation work, PGS reports are routinely accepted by appraisal firms and by insurers familiar with the regional market. The laboratory participates in the broader American gemological community through professional bodies including the AGTA and through continuing-education and trade-show activities.