The History of Diamond Grading: How a Century Changed Carat, Color, and Clarity
How a trade that ran on eye and reputation learned to write quality down — from "first water" to GIA's D-to-Z scale — and why an old estate diamond grade is a starting point, not the final word.
A diamond bought in 1925 and a diamond graded in 2025 may both be described as "near colorless," and the two phrases can mean quite different things. The history of diamond grading is, in large part, the history of how a trade that ran on eye and reputation learned to write down what it saw. For anyone considering a stone that has already lived a long life, that history is practical knowledge. It explains why an old grade deserves respect, and why it should never be treated as the final word.
Before Grading: Diamonds Judged by Eye and Reputation
For most of the trade's long past, there was no common language for quality. By the late nineteenth century, brokers marked stones with Roman numerals or the letters A, B and C, and each house meant something a little different by them. Color was judged by daylight, famously north light through a window, and New York dealers eventually settled on a fixed window of hours, roughly ten in the morning to two in the afternoon, when the light was thought most reliable.
The vocabulary that survives from this period is geographic and romantic. "Cape" described the pale yellow stones that came from the Cape of Good Hope region. "Jager" referred to the strikingly white stones associated with the Jagersfontein mine, and "Wesselton" to a grade named for another South African source. "River" and "first water" were reserved for stones of exceptional transparency, a usage that long predates South African production; the finest early diamonds of India, among them the legendary Golconda diamonds, were admired for just this watery clarity. "Blue-white" meant a stone so colorless it seemed faintly cool, and it was applied with great generosity. In the United States, the Federal Trade Commission's Jewelry Guides still caution that the term is deceptive for any diamond that shows a trace of color other than blue under north daylight.
None of these words was regulated, and their modern equivalents are debated even among specialists. A "Top Wesselton" from a reputable house reflected real experience, but it was a judgment, not a measurement.
The Carat Becomes a Standard
Even the carat, the one measure the trade had always shared, was not uniform. Before the twentieth century, each country and port kept its own carat, with values ranging from roughly 187 to 216 milligrams. In 1907, the General Conference on Weights and Measures in Paris adopted the metric carat of 200 milligrams, one-fifth of a gram. France made it compulsory soon after, and the United States followed on July 1, 1913.
The carat is divided into 100 points, so a stone of 75 points weighs three-quarters of a carat. An old bill of sale for a "one-carat" stone from before 1907 therefore calls for caution: the weight may have been stated in a local carat, or estimated rather than measured. Weight is the easiest characteristic to verify today.
The Gemological Institute of America and the 4Cs
The next chapter in the history of diamond grading began in 1931, when Robert M. Shipley, a former retail jeweler, founded the Gemological Institute of America in Los Angeles. Shipley set out to professionalize an American trade with little formal training, beginning with a correspondence course in gemology. In the early 1940s he is credited with the idea of the 4Cs (color, clarity, cut and carat weight) as a teaching mnemonic, a memory aid for the four factors that define a faceted diamond. The phrase spread through lectures, courses and advertising until it became the trade's common language.
Shipley and his colleague Richard T. Liddicoat also built instruments to support the idea. In 1941 they introduced the GIA Colorimeter, which compared a stone against a graduated wedge of glass running from colorless to yellow. It was an early attempt to replace impression with reference.
The 1953 System: Color from D to Z, Clarity from FL to I3
The decisive step was the GIA International Diamond Grading System, introduced under Liddicoat's direction in 1953. Its color scale runs from D, colorless, to Z, with the letters descending through increasing traces of yellow or brown. The scale begins at D, not A, by design. By then, "A," "AA" and "AAA" had been used so freely that they had lost all meaning, and a fresh start at D, a letter without those associations, broke cleanly from the inflated systems that preceded it. Just as important was the discipline behind the letters: controlled lighting, a neutral viewing environment, and master stones against which a diamond is compared.
Clarity received the same treatment. Liddicoat and GIA colleague Lester Benson devised a scale of precise categories, and the gemological microscope became part of the grader's equipment. Today it comprises six categories and eleven grades, from Flawless (FL) and Internally Flawless (IF), through the very, very slightly included grades (VVS1 and VVS2), the very slightly included grades (VS1 and VS2) and the slightly included grades (SI1 and SI2), to Included (I1, I2 and I3). Inclusions are assessed under magnification and recorded on a plotted diagram.
A formal grading report followed within a few years of the 1953 system. These documents, and later the shorter dossier, gave the trade something it had never possessed: an independent opinion, issued by a laboratory with no stake in the sale, written in a vocabulary that every other laboratory and dealer could read. Laser inscription of the report number on the girdle, which can be read only under magnification, eventually allowed a stone to be matched to its paper with confidence.
Cut, the Last C to Be Graded
Cut resisted objective grading for decades. Marcel Tolkowsky had published his mathematical analysis of ideal round brilliant proportions in 1919, and it influenced cutters and graders for generations, but a durable system for grading finished proportions required far more research. GIA spent more than fifteen years on the problem, using computer modeling and thousands of observations of real stones. It announced its cut grading system for standard round brilliants in 2005, and cut grades began to appear on its reports on January 1, 2006. The scale runs from Excellent to Very Good, Good, Fair and Poor.
The scope matters. The cut grade applies to round brilliants, not to fancy shapes and not to the older cuts at the heart of an estate collection. Those earlier stones were cut by hand, to preserve weight and to suit candlelight, and were never meant to be measured against the modern ideal.
What Estate Buyers Should Know About Old Diamond Grades
With that history in view, the guidance for an estate diamond is straightforward. A grade written decades ago, whether on an appraisal, a family receipt or an early report, reflects the standards, instruments and practices of its day. It is a valuable clue to a stone's history, but it is not equivalent to a current laboratory report. Grading remains a skilled judgment made on a scale, and a stone near the boundary between two grades can fairly fall on either side. The differences are usually modest, but a single grade can matter.
Old cuts are judged differently, too. GIA does not assign a cut grade to an old European brilliant, acknowledging that such stones were not cut to the same standards as today's round brilliants, and in 2015 it added a similar "circular brilliant" category. Because an old European or old mine cut is typically cut with a larger culet, a smaller table and deeper pavilion, it can face up warmer or glow differently than a modern stone of the same color grade. Our guide to antique diamond cuts explains how to read these stones, and why collectors prize them.
A mounted stone is also harder to grade than a loose one, since the setting can influence how color and inclusions appear.
The practical advice is simple. Treat an old grade as a starting point and confirm the stone with a current report from a respected laboratory, ideally unmounted if the piece allows. Check that any inscribed number matches the report, and compare the report to what you see in good light. For a fuller checklist, see our guide on how to buy estate jewelry.
None of this diminishes an old stone. A diamond with an earlier grade has often outlived the language once used to describe it, and a current report simply translates it into the one we all read today. Our selection of estate diamond rings and other diamond jewelry is chosen with that understanding, and each piece is documented honestly. The wider range of vintage and estate jewelry we offer is held to the same standard.
Over the last century, how diamond grading changed was less a matter of diamonds than of discipline. The metric carat standardized weight in 1907, GIA gave color and clarity a shared vocabulary in 1953, and a cut scale arrived in 2006. Knowing the history of diamond grading makes an estate diamond easier to appreciate, and easier to buy well.
The best way to judge a diamond remains to see it. If a stone has caught your attention, request a private viewing and we will show it to you in person, beside its documentation.