The short answer
Robert M. Shipley, an American retail jeweller who founded the Gemological Institute of America in 1931. He coined the four Cs in the years around 1940 as a memory aid for his students: colour, clarity, cut, carat weight. Four words, one letter, and a trade that had never agreed on how to describe its own product suddenly had a shared checklist.That is the answer, but it hands most of the credit to the wrong man. A mnemonic is not a grading system. The person who turned four words into something two strangers could apply to the same stone and get the same result was Richard T. Liddicoat, GIA's president from 1952 to 1983, working with Lester Benson, Joseph Phillips, Robert Crowningshield and Bert Krashes. Shipley named the problem. Liddicoat's team solved it.
How the four Cs became a measurementDates from GIA's own histories and its journal Gems & Gemology. GIA dates the phrase to the early 1940s; the same journal traces the underlying concept to 1930s work between Shipley and De Beers, and records the American Gem Society adopting the terminology in 1939.
1931
Shipley founds the Gemological Institute of AmericaA retail jeweller from Wichita who had spent years selling stones nobody could describe consistently, and decided the fix was to train the trade.
1939
The four Cs enter the tradeThe American Gem Society, which Shipley also founded, adopts colour, clarity, cut and carat weight as its terms for describing a diamond.
1941
The first set of master stonesShipley, Dorothy Jasper Smith and Richard Liddicoat assemble diamonds of known colour to grade other diamonds against. A scale needs something physical to point at.
1953
D to Z, and the first grading reportsLiddicoat, by then GIA's president, publishes the colour and clarity scales still in use, and GIA issues its first diamond grading reports.
2006
Cut finally gets a gradeAfter fifteen years of modelling and observation, round brilliants start carrying an Excellent-to-Poor cut grade. Fancy shapes still do not.
2025
The language splits in twoGIA stops applying D-to-Z and the clarity scale to lab-grown diamonds, describing them as Premium or Standard instead.
Before there was a scale
It is worth understanding what Shipley was reacting to, because it explains why the system looks the way it does. Until the 1950s, a jeweller describing a diamond reached for whichever of a dozen vocabularies they had grown up with, and none of them meant anything you could check.This is also the answer to the question everyone eventually asks: why does the colour scale start at D? Not because A, B and C were taken by better stones. They were taken by nothing in particular, which was the problem. Liddicoat wanted a scale that could not be confused with the letters already in circulation, so he started at the first letter nobody was using and ran it all the way to Z. Choosing a letter with bad associations was deliberate. It made the grade impossible to inflate by adding another A.
What a diamond was called before 1953
Blue-whiteTrade slang
Sold as the finest white a diamond could be. In practice it was often applied to stones with strong fluorescence, which can read hazy in sunlight. The term was abused so thoroughly that American regulators eventually moved against it.River, waterOld European trade
Metaphors for the most colourless stones, on the reasoning that clear water is the highest compliment you can pay a diamond. Poetic, and completely unmeasurable.CapeCape of Good Hope
A geographic term that became a quality term. Diamonds from that region often carried a faint yellow, so Cape came to mean tinted, wherever the stone was actually mined.Wesselton, top WesseltonA South African mine
The same idea running the other way: a mine known for whiter rough lent its name to a grade band. You were buying an association with a hole in the ground.A, AA, AAAIndividual firms
Every company ran its own letters, and no two agreed on what an A was. A firm could add another A whenever it wanted a stone to sound better.Every one of these terms was a claim the buyer had no way to test.
Worth rememberingThe four Cs were invented as consumer protection. A trade that had spent a century selling stones on adjectives was made to sell them on measurements instead. Every time a grade tells you something you did not want to hear, that is the system working as designed.
How a grader assesses them
Two of the four Cs are not judged at all. Carat weight goes on a scale, to the hundredth. Cut is calculated from measured proportions. Neither depends on anyone's opinion, which is why they are the most comparable numbers on any report.Colour and clarity are different. Colour is still done the way Liddicoat set it up in 1941: the stone is laid face down in a tray under a standardised light, against a neutral background, beside master stones of known grade, and the grader decides which two masters it falls between. At GIA a minimum of two graders enter grades independently, and more are brought in until they agree. The grade on the report is a consensus, not one person's call.Clarity is a ten-power loupe and a microscope, mapping where the inclusions sit and how visible they are. That plot on the back of the report is the grader showing their work.
Everything on a modern report descends from decisions made in a Los Angeles classroom in the 1940s.Which is also why two labs can disagree about the same stone by a grade. Colour is a human comparison against physical references, and house standards drift. We cover how much they drift, and which labs to trust, in which grading lab to trust.
Cut took another 53 years
Here is the oddity in the history. Cut is the C that does the most for how a diamond actually looks, and it was the last one to get a grade. Colour and clarity were on reports from 1953. A cut grade did not appear on a GIA report until January 2006.The delay was not neglect. Colour and clarity can be judged by looking at a stone. Cut is a question about what light does inside it, and answering it properly needed computing power the 1950s did not have. GIA spent fifteen years ray-tracing 38.5 million combinations of proportions, then checked the model against more than 70,000 human observations of 2,300 real diamonds before it would put a grade on paper.
One round brilliant, scored on seven components
Two things follow from this that matter when you are shopping. The first is that a cut grade is a floor, not an average: one weak component caps the whole stone, so an Excellent has no weak spots anywhere. The second is that the grade only exists for round brilliants. There is still no official cut grade for ovals, emeralds, pears or cushions, because their facet patterns are not standardised enough to model. On a fancy shape you are back to looking at the stone, which is the older skill and still the better one.Appearance
BrightnessExcellent
FireExcellent
ScintillationExcellent
Design
Weight ratioVery Good
DurabilityExcellent
Craftsmanship
PolishExcellent
SymmetryExcellent
Cut grade on the reportVery Good
The system is deductive: the overall grade is the lowest of the seven, never an average of them. Component names and the rule are GIA's, published with the cut grading system it launched in January 2006. The grades shown are an illustration, not a real stone.Do they apply to lab-grown?
Physically, yes. A lab-grown diamond is carbon in the same crystal structure, so it takes colour grades, clarity grades and a cut grade exactly as a mined stone does. Nearly every lab-grown diamond sold today, including every lab-grown stone we sell, arrives with an IGI report using the full four Cs vocabulary. The natural stones we sell usually carry a GIA report instead.Politically, it got complicated in 2025. GIA stopped applying the D-to-Z and clarity scales to lab-grown diamonds in October that year and replaced them with a two-tier description: Premium or Standard, or no assessment at all if a stone falls below the Standard threshold. Its argument is that more than 95 per cent of lab-grown production lands in a narrow band at the top of both scales, so the fine distinctions have stopped carrying information.
Our readThere is something in the argument. A scale designed to separate stones across a wide natural range does compress when the product is manufactured to sit at one end of it. There is also something in the fact that GIA grades fewer than five per cent of lab-grown diamonds and makes its living from the mined market. Either way it changes nothing about the stone in front of you, and IGI, which grades most of the category, still reports the four Cs in full.
The fifth C
There is no fifth C. GIA has never added one, and a diamond advertised as a 5C diamond is being sold to you with a marketing term, not a grading term.That said, when people say fifth C they almost always mean certification, and as an addition it is a fair one. The four Cs only mean something if a laboratory you can name has signed for them, which is why a stone with no report is not a bargain, it is an assertion. Others have tried to add cost, character, confidence and conflict-free to the list. Those are advertising. Certification is the only one that earns its place.The same question often arrives alongside another piece of trade slang: the poor man's diamond. It is not one stone. It has been used for white sapphire, white topaz, colourless quartz (the crystals sold as Herkimer diamonds), and now most often cubic zirconia. What they have in common is that none of them is a diamond, and none of them is graded on the four Cs at all, because the scales were built for one mineral. If you want a diamond and the budget is the constraint, a lab-grown stone is the honest answer. A simulant is a different stone wearing the name.
What a carat cost in 1970
Around 1,800 US dollars wholesale for a top-quality one-carat stone, which is roughly fifteen thousand in today's money. Treat that figure gently. Published price series for the era disagree with each other by a factor of three, because there was no public benchmark before the Rapaport list started circulating in 1978. Everything before that is reconstructed from trade records of a market a single company controlled.
One carat, top quality, wholesaleNominal US dollars, not adjusted for inflation
The column that matters is not 1970. It is 1980. In the late seventies investors decided diamonds were an inflation hedge, and the price of a one-carat D flawless went up roughly thirty-fold in four years. By February 1981 it had already fallen from around sixty thousand US dollars to forty-four thousand, and it kept going. Anyone who bought at the top has still not recovered, forty-five years later.We include this because the four Cs get mistaken for a valuation system, and they never were one. Shipley and Liddicoat built a vocabulary for describing a stone accurately. What the market then chooses to pay for a D flawless is a separate question, and the answer has moved by a factor of thirty inside a single decade. Buy a ring because you want to wear it.$350
$900
$1.8k
$62k
$14.5k
$19.5k
$13.5k
194719601970198019902010Today
Figures before 1978 are reconstructed from London trade records; later ones follow the Rapaport benchmark. Published series disagree, some by a factor of three on the same year, so read the shape rather than any single column. Australia has no equivalent long-run series of its own.What they never measured
The four Cs do not describe how a stone looks on a hand. They say nothing about whether a diamond reads milky in daylight, how it behaves under a restaurant spotlight, or whether the shape suits the person wearing it. A report is a description of a stone in a laboratory, not a prediction of how you will feel about it.The grades are not even permanent. The best illustration is the most famous diamond of the last century. In 1966 a 240.80 carat rough came out of the Premier Mine in South Africa; Harry Winston cut it into a 69.42 carat pear. Cartier bought it at auction in 1969 for 1.05 million US dollars, a record at the time, and Richard Burton bought it from Cartier the next day for Elizabeth Taylor. She wore it as a necklace, because it was too heavy for a ring.It was graded internally flawless. By the time Taylor sold it in 1979, after years of being worn rather than admired in a vault, it reportedly graded VVS2. Robert Mouawad, who bought it later that year, had it recut to 68.09 carats to recover the top grade, which is what it took: grinding away a carat and a third of the most famous diamond in the world. As for who owns it now, Mouawad has since sold it to a private collector who has not been named, and the stone has not been seen publicly in years.
What to take from thisA grade is a snapshot of one stone on one day, from one laboratory. It is a far better thing to have than the blue-white and top Wesselton it replaced, and it is still not the same as looking at the diamond.
Reading a report and not sure?Send us the grades, or the report number. We will tell you plainly what they mean for how the stone will look on a hand, and where the seller has rounded in their own favour.
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