I have to say, I did a TON of research on diamonds before making the purchase. I actually purchased one last year, only to decide (a) I wasn’t ready and (b) I wasn’t in love with the ring. This year, I finally decided I was ready and set out to find the perfect ring. I spent hundreds of hours scouring www.pricescope.com, which is a great resource for consumers. There are a lot of helpful people on that board.
I learned all about the 5 Cs (cost, cut, carat, color, and clarity) — I listed those in the order of importance to me. As it turns out, carat, color, and clarity are pretty easy to understand. For carat, I decided that anywhere between 1-1.5 carats would look good on her hand — this is based on the average face-up size for a round brilliant and her size 5 ring finger. For color, I wanted something that appeared white. The last diamond was an “I” color, but I decided I didn’t like the warmth when the diamond was viewed from the side, so this time, I went with an “H”, which is generally accepted as appearing white. For clarity, I only wanted it to be eye clean — meaning no inclusions can be seen with the naked eye. Turns out I can’t even see the inclusions in the VS2 clarity diamond I bought with a loupe!
The most important Cs — cost and cut — were more difficult to assess, but for different reasons. Cost was difficult because I had to get over the mental hurdle of spending so much money for a small clear rock. The breathtaking beauty of a well-cut diamond really helped seal the deal. Anyways, I decided I was OK with spending anywhere under $10K for the ring (I paid $8,300 for the diamond).
Cut was by far the most difficult factor to understand. At first, I was undecided between a round brilliant cut and a vintage cushion cut. The latter is actually very unique/classic looking and rivals the beauty of the former. The only problem with the cushion was (a) there was a slight premium for the particular diamond I was interested in and (b) the cushion looks much smaller than it is (i.e., a 1.5 ct vintage cushion looks like a 1.0 carat round brilliant). I decided to go with the round brilliant. This makes life somewhat easier.
But there is a lot to learn about round brilliants. It is a 57 facet structure (58 if you count the point at the bottom, i.e., culet).
Together, these facets work together to reflect light back to the viewer. The light performance of a diamond is measured by its brightness (the amount of white light reflected back to the viewer and the contrast of the virtual facets), fire (the colored light reflected by the virtual facets), and scintillation (the way light reflects off the virtual facets when the diamond is moved). (Virtual facets refers to the facets that can be seen from the face of the diamond — most of these are not actually one of the 57 or 58 facets, but a reflection of a reflection, etc. of a facet.)
There are a few ways for a consumer to determine the cut quality of a diamond. First and foremost, a diamond larger than 0.5 carats should be accompanied by a grading report. The best grading reports come from GIA and AGS. The best GIA rated diamonds are “excellent” and the best AGS rated diamonds are “0” — meaning no deduction. There is still, however, a wide discrepancy among GIA excellent and AGS “0” diamonds. The next place a consumer can turn is to the Holloway Cut Adviser (HCA) at http://www.pricescope.com/tools/hca. The HCA tool is a rejection tool — meaning a diamond having a score greater than 2 should be weeded out, but a diamond with a score under 2 shouldn’t necessarily be purchased on the score alone. The HCA takes as inputs the table size, depth percentage, crown angle and pavilion angle. The latter two have an important inverse relationship, wherein a lower crown angle should be accompanied by a higher pavilion angle and vice versa. There is, of course a sweet spot in the proportions of a round brilliant diamond. Look for diamonds having tables of 53-58%, depths of 60-62% (a smaller depth will result in a larger looking diamond), crown angles of 34-35%, and pavilion angles of 40-41%. While a low scoring diamond is desirable, the HCA is not perfect. This is because on diamond grading reports, diamond proportions are averaged (8 crown angles, 8 pavilion angles, etc.). If a diamond has some asymmetry (all of them do to varying degrees), then it might negatively affect the optical performance of the diamond in a way that the HCA cannot account for.
After using HCA to select some promising candidates, consumers should go one step further and view the diamond under an optical imaging tool, such as Idealscope or ASET. More and more online websites are routinely offering these images for diamonds in their in-house inventories. Websites with virtual inventories will typically offer such images upon request. Traditional brick and mortar stores generally do not offer these tools, which is why some savvy consumers buy their own (they are relatively inexpensive).
In an Idealscope image, the red areas indicate light is being reflected back to the viewer (the more red the more intense the light return is), the black areas indicate contrast, and white areas indicate light leakage. This is an example of a superbly cut diamond. Generally, consumers should avoid diamonds having leakage under the table — in this case the only leakage is along the edges of the diamond, which is present in even the best cut diamonds.
Here is an ASET image from whiteflash.com:
In an ASET image, red is the most desirable, meaning direct light return. Blue indicates contrast and green indicates indirect light return (this is less desirable). White (or black depending on the background) indicates light leakage. Green and white (or black) should be minimized in a well-cut diamond, as it is in this example. The ASET provides more information about the direction of light and should be viewed when available.
Now, these imaging technologies tell us a lot about what is happening with the major facets, but not so much about the 40 minor facets. The minor facets play a very important role in the appearance and light performance of a diamond. Here is a brief tutorial on the minor facets: http://www.goodoldgold.com/Articles/MinorFacets/. Consumers should determine the star/lower girdle facet combinations they like the most — this information is available from the diamond grading report or from a diamond scanner report (e.g., Sarin or Helium). Consumers should also verify with the vendor that the diamond they are interested in buying does not have cheated girdles (unless desired).
Some online retailers of diamonds offer objective testing of their diamonds to measure optical performance. One example, is the GemEx BrillianceScope, which measures brilliance, fire, and scintillation under direct lighting. bScope gives ratings in each category from Low, Medium, High, to Very High. Another example is Isee2, which measures brilliance, contrast, fire, and optical symmetry under diffuse lighting. Isee2 provides a composite score out of 10. Goodoldgold provides ratings for all of its signature round diamonds. For example, this one. Of course, no system is perfect and ultimately the decision should be made with your eyes.
Lastly, a lot of consumers are interested in hearts & arrows diamonds. Hearts & arrows refers to the virtual facet patterns that can be viewed from the table and pavilion. Here is an image showing what arrows look like from the table and what hearts look like from the pavilion.
Of course H&A patterning comes at a price premium. Some think it is worth it, others don’t. A lot of ideal cut diamonds have the arrows patterns, but not the hearts pattern, but the hearts pattern can’t be seen once the diamond has been mounted anyways.
A lot of my research has been done online. Now that I have an actual diamond in hand, I realize how important lighting is in viewing diamonds. Diamonds look completely different in direct sunlight, diffuse lighting, spot lighting, etc. My next mission is to compare my diamond with other superideal cut diamonds, such as Hearts on Fire and Isee2 to make sure that I’ve gotten one of the best, for the best price possible. I will post about that process, in addition to setting, insurance and appraisal at a later time.
EDIT: by request, here is a picture of the ring I purchased: