A GRS report is one of the most common documents you will see attached to a high-value ruby or sapphire, and it is also one of the easiest to misread. If you want to know how to read a GRS gemstone report, the short answer is to focus on four things: the identification, the treatment statement, the origin line, and the color description. This guide walks through each so you can compare stones with confidence.
What a GRS Report Is and Who Issues It
GRS is the abbreviation for GemResearch Swisslab, an independent gemological laboratory founded in Switzerland that also operates in Asia, including Bangkok. Along with GIA, SSEF, Gübelin and a few others, it is among the laboratories the colored stone trade routinely accepts for important rubies and sapphires. Because the trade values these reports differently depending on the stone, the lab name matters, but the content of the report matters more.
Every report carries a unique number, usually printed alongside a photograph of the stone and its measurements. Treat the report and the stone as a pair: the weight, dimensions, shape and cut style on the paper should match the gem in your hands. If a seller cannot show you how to verify the number with the issuing lab, ask why.
The Identification Section: Species, Variety and Measurements
The first block tells you what the stone is. For our purposes it should read natural corundum, with the variety given as ruby or sapphire. This is the line that separates a natural gem from a synthetic or a composite, so read it carefully rather than skipping straight to the origin.
Below that you will find the carat weight, measurements in millimeters, shape and cut. Compare these to the stone itself. A stone that measures noticeably differently from its report may have been recut, which can change both its value and the validity of the document. Remember too that weight is rounded, so tiny differences in the second decimal are normal.
The Treatment Statement: The Most Important Line
For most buyers, the comment on thermal treatment drives price more than anything else. Reports use specific, standardized wording, and each phrase means something different:
- No indications of heating: the lab found no evidence that the stone was heat treated. This is the wording associated with unheated stones and the premium that comes with them.
- Heated: the stone has been heat treated, which is by far the most common and widely accepted enhancement in corundum.
- Heated with residues or fillers noted: any mention of glass or other material filling fractures is a major flag. Stones like this are worth a fraction of an ordinary heated stone, and the report should disclose it plainly.
Note the careful phrasing. A lab states what it can observe, so “no indications of heating” is a finding based on the evidence, not a guarantee in every case. If you are paying an unheated premium, read this line twice and make sure the rest of the report is consistent with it. Our own unheated sapphires are sold with the treatment status stated clearly, and heated sapphires are disclosed just as clearly.
The Origin Line and Why Not Every Report Has One
Origin determination is a separate analysis that compares a stone's inclusions and trace-element chemistry with reference samples from known localities. When a report states an origin, it will name a country such as Burma (Myanmar), Sri Lanka, Madagascar, Mozambique or Thailand. Some reports issue a stronger or weaker conclusion depending on how conclusive the evidence was, and some stones simply cannot be assigned to a locality.
Many reports do not include an origin at all, either because the client did not request it or because the lab could not determine one. That is not a red flag. A stone without an origin statement is still a legitimate stone, but it should be priced as one. Do not pay an origin premium that the paper does not support.
Color Descriptions and Comments
Reports often describe color in words, and top-grade descriptions such as “pigeon’s blood” for ruby or “royal blue” for sapphire can carry a significant premium. Treat them as the lab’s professional opinion of the color, not as a mathematical grade. Two stones with the same wording can still look different in person, so judge the gem itself.
Finally, check the comments section at the bottom. It may note additional information, such as the presence of silk or other features, or caveats about the testing. This is where honest labs put the details a buyer should know.
A Quick Checklist Before You Buy
Confirm the report number, match the weight and dimensions to the stone, read the treatment line carefully, check whether an origin is stated, and compare the price to what the report actually supports. A report is only useful if the stone in front of you is the stone it describes.
At Thai Gems, we have handled sapphires and rubies since 1963, and we encourage buyers to ask questions about any report we supply. Browse our current selection of ruby solitaires and sapphires at thaigems.com, or contact us for trade pricing and details on certified stones.