Gemological reports — what do they tell us, and when do you need one?
When choosing a diamond or a gemstone, one of the questions that comes up is: “Does the stone have a certificate?”
It is an important question, but it is also worth asking which certificate, who issued it and exactly what was examined.
Not every document accompanying a stone provides the same information. A diamond grading report, a sapphire identification report and a jewelry appraisal are different documents, intended to answer different questions.
What is a gemological certificate?
In everyday language we say “certificate,” but in many cases the more precise term is “gemological report.”
It presents the results of a laboratory’s examination of the stone. Depending on the report, it may include identification, weight, measurements, quality characteristics, detected treatments and sometimes an opinion on geographic origin.
The report concerns the stone examined and its condition at the time of testing. It is not a promise that the stone will not break, a jewelry warranty or necessarily an appraisal.
A document provided by a seller is not necessarily an independent laboratory report. It is important to understand who issued it and the scope of the examination.
What appears in a diamond report?
A comprehensive natural diamond grading report generally includes the four familiar measures:
- Carat weight: the diamond’s weight in carats. One carat equals 0.2 grams.
- Color: for diamonds in the normal color range, a grade describing the degree of colorlessness.
- Clarity: a grade addressing internal inclusions and external characteristics.
- Cut: an assessment of cut quality, where the type of diamond and report allow it.
Other details may include measurements, shape, cutting style, polish, symmetry, fluorescence and comments. Some report formats also include a plot of inclusions.
It is important to distinguish the stone’s shape — round, oval or pear, for example — from its cut quality. They are different things.
Not every report includes an overall cut grade. At GIA, for example, the standard cut grade in reports for natural diamonds in the normal color range applies to standard round brilliant diamonds.
What about colored and laboratory-grown diamonds?
For a colored diamond, check not only the color description and grade, but also whether the color is natural or the result of treatment.
There are different report types here too: an identification and color origin report is not necessarily a full grading report.
For laboratory-grown diamonds, the document should clearly state that origin. Report types and grading systems can differ between laboratories, so read the particular report rather than assuming all documents follow the same format.
How does a colored gemstone report differ?
A report for a sapphire, ruby or emerald generally emphasizes the stone’s identity and treatments.
Depending on the laboratory and service, the report may state:
- The gemstone’s species and variety.
- Whether it is natural or laboratory-grown.
- Weight, measurements, shape and cutting style.
- A description of color and transparency.
- Treatments detectable during the examination.
- An opinion on geographic origin, where the service includes it and sufficient evidence is available.
Unlike diamonds, colored gemstones do not have an equally uniform and widely accepted grading system for color, clarity and cut.
A report identifying a stone as natural sapphire therefore does not establish on its own that it is of exceptional quality. The stone’s color, clarity, cut and appearance still need to be examined.
Can the stone’s country of origin be determined?
For some gemstones, a geographic origin opinion is available.
The laboratory examines inclusions, growth characteristics and chemical composition, comparing the findings with stones from known sources.
This is a professional conclusion based on the evidence found in the stone. A determination is not always possible, and stones from different locations may have overly similar characteristics.
Distinguish a gemological origin opinion from documentation tracing the stone from mine to seller. A standard origin report does not necessarily provide that documentation.
How do laboratories differ?
Laboratories differ in expertise, equipment, reference collections, report types and terminology.
Here are some examples:
| Laboratory | Examples of services |
|---|---|
| GIA | Natural diamond grading, colored diamond testing and colored gemstone identification, including treatments and origin opinions where applicable. |
| IGI | Reports for natural and laboratory-grown diamonds, alongside colored gemstone and mounted jewelry reports. |
| GRS | Colored gemstone reports covering identification, treatments and origin opinions where determinable; in some cases, color designations according to its criteria. |
| SSEF and Gübelin | Colored gemstone testing, including treatment identification and geographic origin opinions. |
| Lotus Gemology | Colored gemstone identification and treatment reports, with origin opinions where the findings allow them. |
This list is not a ranking and does not cover every service offered by each laboratory.
Alongside professional capabilities, the recognition of a report in the market where a stone is bought or sold also matters. The laboratory should therefore suit the stone, the question to be examined and the purpose of the report.
Trade color designations are not necessarily based on the same criteria at every laboratory. Understand what a designation means at the laboratory that issued the report.
Does a certificate tell you what the stone is worth?
For diamonds, a grading report also provides a basis for comparing prices. Weight, color and clarity allow comparison with diamonds having similar characteristics and reference to price lists commonly used in the trade. The report does not set a price by itself, but provides an important indication for assessing it. Cut and other characteristics also affect the actual price.
Colored gemstones have no uniform, widely accepted price list comparable to those used for diamonds. Two stones of the same type and weight may differ greatly in color, clarity, cut, treatments and appearance — and accordingly in price.
A gemstone report therefore provides important information for assessing value, but does not translate its findings directly into a price. Examination of the stone itself and market knowledge are also needed.
In both cases, a gemological report and an appraisal are different documents.
Does every stone need a certificate?
Not necessarily.
For a valuable stone, or where the price rests on a significant claim — such as absence of heating or a particular geographic origin — a suitable independent laboratory report can be especially important.
For a relatively inexpensive stone, testing and shipping costs may represent a large part of its price. Consider what you want to establish and the benefit of the report.
Several small stones mounted in a piece of jewelry do not necessarily require a separate report for each.
The aim is to choose testing that meets the need, rather than obtain a document simply to have one.
How do you check that the report belongs to the stone?
First, check the report number on the laboratory’s official website, where a verification service is available.
Verifying the number confirms that such a report exists — it does not, on its own, prove that the stone in front of you is the one examined.
Compare the weight, measurements, shape and documented characteristics as well. Some diamonds have a laser inscription on the girdle that can help with matching alongside the other details.
If the stone was recut or treated after testing, the old report may no longer describe its current condition.
A report is a tool for understanding
A good report can answer important questions and reduce uncertainty, but it does not replace looking at the stone and examining its suitability for the jewelry.
At TzurGems, we consider gemological information alongside appearance, proportions and intended use. When a report is available, we want to understand what it says — and what it does not say.
This helps you choose a stone with an understanding of its characteristics and what they mean for you.