Grading Gemstones and Diamonds

How to grade colored gemstones and diamonds including using the 4Cs --Color, Clarity, Cut, and Carat Weight.

Grading Gemstones and Diamonds

  • Carats are units of measurement for gemstone weight.  The term “carat” may have originated with the ancient practice of using carob seeds as a unit of measure in the Mediterranean and Middle East regions.  The seeds were presumed to have a uniform size and mass.  Today, the carat weight unit is standardized as 200 mg. “Carob (ceratonia siliqua) seeds” by Mihailo Grbic is licensed under CC By-SA 3.0 RS.
    Carats And Gemstone Grading 

    Step 4: Gem Grading Lesson 2 Back to syllabus What are Carats? Carat is one of the four Cs of gemstone grading. In English, that sounds the same as carrot, but we aren’t discussing vegetables. Carat also sounds the same as…

  • Clarity Grading Diamonds 

    Step 4: Gem Grading Lesson 12 Back to syllabus Until the mid-1900’s, purchasing a diamond was very confusing. Dealers used terms like “AA” and “AAA.” These terms meant nothing to the average consumer and, to make things…

  • clarity grading - color change sapphire
    Clarity Grading for Colored Gemstones 

    Don’t underestimate the importance of clarity, one of the Four Cs of gemstone grading. For faceted gems, basic clarity grading involves evaluating qualities such as transparency, inclusions, and blemishes.

  • Canary Yellow Engagement Ring
    Color Grading Diamonds 

    Step 4: Gem Grading Lesson 13 Back to syllabus It is less than a century that gemology has been regarded as a science. Thanks to pioneering work by people like Robert M. Shipley Sr. and B. W. Anderson, a level of accuracy and…

  • Color Grading Fancy Colored Diamonds 

    Step 4: Gem Grading Lesson 14 Back to syllabus Diamonds come in every color of the rainbow. Our standard white diamonds are either colorless or tinted slightly yellow. All other colors are considered “fancy colors.” Fancy…

  • Cut Grading Diamonds Part 1: Traditional Methods 

    Step 4: Gem Grading Lesson 15 Back to syllabus Of the four C’s, cut is the most important. It is the cut, or make, of a gem that determines why one diamond jumps out at you with spectacular fountains of light, while another…

  • Cut Grading Diamonds Part 2: Modern Methods 

    Step 4: Gem Grading Lesson 16 Back to syllabus In 2005, the GIA introduced a new method for grading diamond cut. There are many advantages to the new methodology, not to mention that GIA reports are the most common in the…

  • Distinguishing Diamonds 

    Step 4: Gem Grading Lesson 10 Back to syllabus A prerequisite to diamond grading is knowing how to tell diamonds from their lookalikes. It does no good to assign color, clarity, and cut grades to a gem, if you cannot tell if it…

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    Evaluating Gemstone Cutting: The Five Ps 

    In recent decades, something remarkable invaded the thinking process of the colored stone industry. From dealers to consumers, they all discovered “The Cut.”

  • gemstone grading - diamonds and colored gems
    An Introduction to Gemstone Grading 

    Step 4: Gem Grading Lesson 1 Back to syllabus The Diamond Four Cs Standard Until the 1930s, no standards for gemstone grading existed. When the Gemological Institute of America (GIA) instituted the four Cs method for grading…

  • Grading Gem Carvings 

    Step 4: Gem Grading Lesson 6 Back to syllabus Gem carvings vary widely in size, shape, and quality. You can find small, simple carvings with a glued-on bail for just a couple of dollars.  Fine carvings from gem grade material…

  • Set Gemstones - Diamonds
    How To Grade Set Gemstones 

    Step 4: Gem Grading Lesson 4 Back to syllabus Few gemologists deal strictly with loose stones. Most may occasionally have to grade set gemstones. Mounted stones can’t be graded the same way as loose stones. They require special…

  • Guide to GIA’s Diamond Cut Grading System

    The Gemological Institute of America (GIA) grades the cut of a diamond as either; Excellent (the best grade) Very Good Good Fair Poor (the worst grade) Below are the details that will help you understand GIA’s diamond cut grading…

  • gemstone value - tourmaline Tanzania
    Advice for Determining Gemstone Value 

    Many new gemologists buy low-quality gems believing they’ve found a real bargain. However, judging gemstone value is very complex.

  • Well Polished vs. Poor Polish
    A Consumer’s Guide to Gem Grading

    Gems are graded by four qualities, known as the “four C’s.” These stand for Color, Clarity, Cut, and Carat, (meaning size.). The first thing a consumer needs to understand is that gemstones are graded by the rarity of their features. Even…

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    How to Choose a Diamond

    Diamonds are the most popular gem used in jewelry today. They have great brilliance, plus a delightful quality know as dispersion. That is the ability to take in white light and throw back flashes of color or “fire.” Diamonds are graded into…

  • Common Sense Gemstone Grading - Subjective Terms
    Common Sense Gemstone Grading: An Alternative System

    I don’t agree with the Gemological Institute of America’s (GIA) grading system for colored gems. I don’t believe in creating “types” of gemstone categories and adjusting the grading scale to fit what is most common or what some trade groups want…

  • Marquise Cut Setting
    Grading Fancy Shape or Fancy Cut Diamonds

    What is a Fancy Shaped or Fancy Cut Diamond? When discussing diamonds, a “fancy shape” is anything other than round. Fancy shapes are cut to to obtain maximum yield from odd shaped rough. While less common than an octahedron, many broken…

  • Just Ask Jeff: Colored Stone Grading System

    Colored Stone Grading System I use and recommend my own colored stone grading system. Common Sense Gemstone Grading – by Jeff R. Graham copyright 2007 This is the Gem Institute of America’s colored stone grading system. I have been told by…

  • chrome tourmaline buying - fancy oval
    Chrome Tourmaline Buying Guide

    Rare chrome tourmaline can show an emerald-like green color. With a highly desired color and tourmaline’s excellent jewelry stone qualities, this gem ranks as one of the top commercial stones on the market today.

  • verdelite - pear cut
    Green Tourmaline (Verdelite) Buying Guide

    Looking for a tourmaline jewelry stone? If you like green and you’re on a budget, green tourmaline or verdelite is the gem for you.

  • Indicolite - Brazil
    Blue Tourmaline (Indicolite) Buying Guide

    Blue tourmalines or indicolites are a popular jewelry stone. However, some of these gems are often misrepresented.

  • rubellite buying guide - pendant
    Rubellite Tourmaline Buying Guide

    Like all tourmaline gemstones, rubellite wears well in almost any type of jewelry. This stone’s raspberry-like color draws a great deal of attention. Rubellite is one of the most popular gems on the market today.

  • Exposing Overgrading at European Gemological Laboratory (EGL)

    On September 9, 2014, the Rapaport Group issued a press release stating, ‘Effective October 1, 2014, EGL will no longer be listed as a diamond grading report on RapNet. This notice applies to all EGL grading reports including EGL International as…

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    FTC Guidelines for Grading the Quality of a Diamond

    According to the Jeweler’s Vigilance Committee (JVC), FTC guidelines now require accurate and truthful representation about the Grading System (GIA, EGL, etc) used to determine the quality of a diamond. Diamond grading has been much in the…

  • Diamond Cut Grading Simplified – The Hanneman System – Lesson One

    The Hanneman System A Basic Course The cut grade of any round brilliant diamond can be derived from the knowledge of four measurements, two equations, and a table of 12 numbers. The measurements are total height, diameter, crown angle, and…

  • Diamond Cut Grading Categories – The Hanneman System – Lesson 3

    Lesson 3: Cut Grade Categories and Taking Out the Garbage Cut Grade Categories Cut diamonds can be fitted into one of five categories. Not renowned for my tact, I simply call them Best, Better, Good, Junk and Garbage. Granted, retailers use more…

  • Diamond Cut Grading Proportions – The Hanneman System – Lesson 2

    Lesson 2: Basic Proportions This is basic geometry, but stick with me. In simple terms, a diamond can be considered as being composed of three components which fit together—a cone, a cylinder and a frustum, i.e., part of a cone shaped solid next…

  • Diamond Cut Grading Simplified – The Hanneman System – Lesson 4

    The Hanneman System A Basic Course The cut grade of any round brilliant diamond can be derived from the knowledge of four measurements, two equations, and a table of 12 numbers. The measurements are total height, diameter, crown angle, and…

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