There are lots of opinions in the jewelry business about which grading lab is best when choosing a diamond. The problem with these opinions is that they're usually fed-up because the person/business giving you the opinion needs to sell you their diamond. Their opinion on which grading lab is best is decided by what lab has graded their diamond, how convenient is that? If they own a diamond certified by EGL then they tell you that EGL is best, if they have another diamond owned by GIA then GIA is best. These are prejudiced opinions and you should be very cautious as to how much weight is given to them at some stage of your decision making process.

How are diamonds certified?

The "Big Three" grading laboratories as I like to call them have similar processes for certifying diamonds. This process involves several Graduate Gemologists separately assessing and approving on the color, clarity, and carat weight of the diamond. This helps reduce the possibility for human error when decisive the final grade for the diamond, although it doesn't eradicate it. You must consider the indubitable fact that there is no exact science behind diamond grading. I know the grading systems echo official and science like but they're really aren't. Consider this statement for a moment, "No two diamonds are exactly alike." With that being said, how could two different diamonds which are not exactly alike be graded exactly alike? In reality they can't be.

The other important fact is that the final quality grades are decisions or opinions not scientific calculations. So if they are opinions and each diamond is graded by dissimilar labs and dissimilar graders then how could there be any consistency? Truth be known, grading labs have a tough time with that, despite of which lab you talking about. Let's say for example, that you send a diamond to GIA for certification and it comes back carat weight - .50ct, clarity-SI2, Color-H. Then, you throw away the certification and send the diamond back for a second grading as if it were never graded before. The chance of it coming back SI2, H again is probably 80% and 20% that it'll come back different. So the grading and certification procedure is somewhat defective to begin with. If you can't get one grading lab to constantly agree with its own grades, how could you expect other labs to agree with another? Again, there's no easy answer to that question and as an industry we still don't have it figured out.

AGS has become very notable for their knowledge about cut and grading a diamond for its potential light presentation. Most of what the jewelry industry uses to agree on if a diamond is optimized for brilliance is based on AGS's research. If a jeweler suspects that a diamond is cut very well then he may send the diamond to AGS for certification. If you are looking for a diamond with a very high cut grade you should consider looking at diamonds that have been certified by AGS.

Final recommendations

Get more involved in the diamond buying process and identify with how the 4C's work, not just what it stands for. Ask to use a jeweler's loupe (eye piece) or a microscope to see the diamond under magnification. When looking at the diamond under magnification inspect the inclusions for each grade you're considering then compare them side by side to determine if one looks better than the other. For example, let's say you are looking at two SI1 diamonds - one is a certified by EGL and the other GIA. After comparing them, you decide that the diamonds look similar but the EGL diamond is 15% less in price. Who cares what lab certified them! Just because some jewelers think that GIA is a better grading lab doesn't make the diamond certified by GIA better. The grading labs don't make the diamonds, they simply grade them, a diamond isn't made better by its certification. A certification is just a piece of paper; you can't put a piece of paper in a ring and propose. If one diamond looks better than another it probably is, regardless of the grade or what lab assigned it. So in this case the logical choice is to get the better looking diamond, forget about what lab is better and save your money.

Don't exclude comparing the color. The best way to do this is to ask to see loose un-set diamonds and then compare them side by side. Take a white piece of paper and place the diamonds upside down and next to one another on the paper. The white background adds contrast to the diamond's color and helps you distinguish the color differences between them. After making a decision on your own about the amount of color a diamond has then refer to the certification to see what the grade is. Again, it doesn't matter who graded the diamond or what the grade is. In the end you need to see it with your very own eyes and trust your instincts about which diamond is right for you.

Diamond certification is certainly significant to have and I don't think you should buy a quality diamond without one. I do believe though, that a strong decision is one that involves you referring to the certification, comparing diamonds side by side, and using your head. Let's not forget the value of working with a highly regarded jeweler as well. A good jeweler lends his/her expertise and provides an balanced opinion about each diamond's characteristics. The final decision about a diamond and whether it's right for you - should be prepared by you. Not a grading lab!