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Diamond Buying Guide From the GIA, edited by Janet Deleuse

What is a GIA Graduate Gemologist (GG)?

The prestigious GIA Graduate Gemologist diploma educates jewelers and appraisers the science and technical knowledge needed to evaluate the entire spectrum of diamonds and colored gemstones.   The distinguished GIA GG designation is  recognized around the world as the mark of a professional in the jewelry industry.

Buying a Diamond Wisely

1) Choose a jeweler as you would choose a doctor.

Your jeweler should be educated and have expert training, open to all your questions and provide answers with clarity.

A measure of a jeweler's knowledge is whether he is professionally trained. Preferably, his training comes from a highly-recognized and internationally accredited program, such as the GIA Graduate Gemologist (GG) or Accredited Jeweler Professional (AJP) diploma programs.

An educated jeweler will explain the 4Cs of diamond buying guide and demonstrate the differences between similar looking diamonds. The jeweler will have the ability to compare a number of diamonds within a specific price range.

2) The 4Cs of Diamond Quality

This basic knowledge will help you understand a diamond's value and price in an overall preview.

Diamond Color    The absence of color ranks the diamond the highest for color rating; D-E-F.  The less overall color hue in the diamond are subtle and these differences are sometimes not visible to the naked eye.   Color hues directly impact the overall quality and price of the stone.

D-E-F  Colorless, G-H-I-J Near Colorless,  K-L-M  Faint Yellow,  N-O-P-Q-R  Very Light Yellow,  S-T-U-V  Light Yellow

Diamond Clarity   Clarity is the degree to which identifying characteristics known as inclusions are present in a diamond. Refers to the quantity, size and placement of internal inclusions and external blemishes.  Grading diamonds based on inclusions are rated beginning with the most valuable termed,  Flawless, a diamond that has no internal or external flaws visible under 10X magnification.  Included, refers to a diamond with  a significant number of imperfections.

Flawless  Internally Flawless, No internal or external flaws visible under 10X magnification

 VVS1-VVS  Very Very Slight Inclusions, Inclusions are minute and extremely difficult to locate under 10X magnification

 VS1-VS2 Very Slight Inclusions, Inclusions are minor and difficult to locate under 10X magnification

 SI1-SI2 Slight Inclusions, Inclusions are noticable and relatively easy to locate under 10X magnification

 I1-I2-I3  Imperfect, Inclusions are obvious under 10X magnification and are visible to the naked eye.


Diamond Cut  Refers to the diamond's proportion and arrangement of its facets and the quality of overall polish, it does not refer the the shape of the diamond. The amount of brilliance, sparkle and fire in a diamond is determined by cut. Grades range from Excellent or Ideal, referring to an ideal proportion in which all light beams will be refracting back to the eye of the beholder from the top of the diamond,  causing the diamond to sparkle. The lowest quality of cut is termed  Poorthis may indicate that the facets are not the correct number or angles and the light beams will be refracted in different directions, to the eye the diamond will not sparkle well.

Diamond Carat  Refers to a diamond's weight which is measured in carats, the standard world-wide measurement for a diamond size.  Large  Diamonds with high carat weight over five carats are rare and therefore, generally  expensive.  It is possible that several diamonds can be of equal carat weight and will vary considerably in quality, therefore, affecting the prices considerably.  

For an overall view, the 4 Cs are considered a good tool for a general evaluation.

3) Your Jeweler should provide a Diamond Grading Report with your purchase.

A diamond grading report from an unbiased, scientific source such as Gemological Institute of America is more than important information, it's proof of what you are purchasing. The differences in diamonds can be so subtle, your certificate will verify your purchase and is exclusive to your diamond.

4) Protect The Purchase.

The jeweler should give you an appraisal for your diamond for insurance purposes. Insurers rely on diamond grading reports to accurately evaluate the value of gems and your appraisal document will allow you to replace your diamond from a jeweler of your choice in case of loss.

Diamond Collection

            For More information call us: 415-459-3739  

           We are located 55 Broadway, Fairfax, Ca     

           OPEN Tuesday-Saturday 10:30-4:30

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Instagram: @janetdeleuse 

Jeff Deleuse

  • B.A. Psychology
  • Advanced French Language, University of Nice, France
  • Stanford Continuing Studies
  • Graduate Gemologist, Certified Appraiser 

Janet Deleuse

  • B.S.  Molecular Biology
  •  Stanford Continuing Studies, Art History and Literature
  • Saul Bell International Jewelry Award Judge, 2015
  • Past Board Marin Advocates for Children, 2014
  • Contributing Writer and Featured Designer in Jane Merrill's book"I Love Those Earrings" 2014
  • Audio Contributor to “Cartier & America” Exhibit at the Legion of Honor, San Francisco, 2010-2011
  • Janet Deleuse Couture Featured in Britex  Newsletter, San Francisco, 2012
  • "Fashion & Impressionism" research paper written in Spring 2011; for exhibit
  • Cartier Achievement Award presented June 2009
  • Women's Jewelry Association Award January 2009
  • Contributing Writer for LUXX International Jewelry Magazine, 2009-2010


  • Graduate Gemologist from the Gemological Institute of America
  • Past Members of the American Gem Trade Association
  • Past American Gem Society
  • Jewelers Of America
  • Women's Jewelry Association
  • Contemporary Jewelers Design Group