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Color

The Gran Colorimeter

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In these chapters on color we will be showing you how these colors actually look as they are compared and graded side by side.  This is the traditional way of grading color which has been done since color grading has been instituted.   In the mid 90's a company develpoped a technology with which color can be digitally measured and analyzed and there have been others since.  We incorporate this technology into our own analysis as well and is one of the 2 ways we grade color here at GOG.

This device is the Gran Colorimeter.



Operation is quite simple really.  Just lift the red hood up top... 



and place the diamond atop the stage inside...



close the hood ...



Press the red execute button ... (we were measuring an AGS graded D color in this instance) and the results are shown in a couple of seconds.



Results are spot on.  

FAQ's on the Colorimeter:

Q1. How accurate is the colorimeter?
A1. Very accurate.  A properly calibrated Colorimeter grades extremely accurate. Just about all of the diamonds we have graded and then double checked against a set of master stones plus confirmed with lab reports demonstrate to us the accuracy of the Colorimeter.  This is the 3rd generation Gran Colorimeter and we have been using it since its inception.  The latest model, the DC3000 has proven to be the best and most accurate machine produced by them to date.  We have had some problems with past models but so far no probs with their latest generation.

Q2. Can fluorescence skew the results?
A2. Not that we have seen.  We have tested many diamonds with fluorescence on the Colorimeter and the presence of fluorescence has not altered the results.

Q3. Does the colorimeter work for fancy colored diamonds?
A3. Yes.

The diamond in this picture is of a fancy brown/yellow.  Below are its colorimeter results.



Q4. When the colorimeter disagrees with a lab report which is correct?
A4. In just about every instance the colorimeter has been correct!  Here's an example.  Both of the diamonds in this photograph were graded as a "J" color.  Can you see which stone has more color in this unedited photo?



If you said the stone on the right you are correct as there is a bit more yellow in that one.

Here are the colorimeter results of both diamonds.



Back to the supplier it goes.  

This however does not mean that the colorimeter is a flawless device. It does show inaccurate results from time to time.

Q5. Do you ever catch labs making mistakes in your favor?
A5. Yes.  

Q6. What would you consider the limitations of the Colorimeter?

A6. One is that it is not always accurate with regards to "D" color diamonds.  Many accurately graded "D" colors will test as "E" on the colorimeter as it has trouble distinguishing between these 2 color grades, both of which constitute less than 1% of diamonds in the world.  Also, it is not always reliable when it comes to fancy shapes. When we color grade rounds we find the device very accurate in most circumstances but we will rely on observation testing upside down against a flat white background for a more accurate grade when it comes to fancy shapes like princess cuts, cushions, asschers, ovals, etc.




 
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Article Contents
1.
2.
3.
4.
5.
6.
7.
8.
The Gran Colorimeter
Colorless
Near Colorless
Faint Tint
Tinted
Fluorescence
Fancy Colors
Color Tips