废话少说， 开讲

1. All about the 4Cs

Any one who is remotely interested in diamonds knows about the 4Cs. Just like all the other good things in life, what's on paper doesn't always translate well in the real world. My lesson is that you really need to see the diamond with your own eyes, and see lots of them to really understand how 4 Cs determine the value of a diamond

--- Carat ---

The carat weight is always the first thing you notice about the stone. If you read the wholesale price list, you would see that the prices make a big jump at 0.5 carat, 1 carat, 1.5 carat, 2 carat, 3 carat, etc. These are called "Magic weights", "magic" in a marketing sense only. The cutter likes to cut the stone at or a little over these weights because they can make a good sale and with higher than usual margins. On the other hand, a stone a little "under weight", say 1.95 carat, costs a lot less money than the 2 carat. And I bet you couldn't tell the difference even under the microscope.  So here is Tip #1, under weight stone is usually a good bargain.

Speaking of 2 carat, I always thought it's huge and is somewhat a milestone, and of course, worth the extra money. Well, I was disappointed when I saw a 2 carat and a 1.5 side by side. It's not a huge difference sizewise, not huge enough for the 80% price increase. When I put the 2 carat and 1.8 carat together? You guessed it, only a teeny tiny bit bigger. After mounting in a setting, nobody can tell who is bigger. A G.G told me there is no meaningful size difference "visually" for these weight ranges - 0.75~1.0, 1.5~1.75, 1.8~2.0. Hence Tip #2,  buyers be aware when you dump big money for the weight upgrade, go see it yourself.

Last, I used "weight" rather than "size" here because carat is not the sole deciding factor of diamond size. Look at this diamond picture, 2 diamonds with the same weight could have diffent table size(the biggest facet from top view), depth(how tall is the diamond), diameter (some round diamonds are really not that round), and spread(over all cut quality and proportions) . I will talk more about this in "Cut", Sarin report ( I posted an example here) is a good tool for you to find out exactly how the diamond is built.

-- Clarity ---

More than often, I see people here make a statement like " I won't go below vs1", "only buy clarity over vvs2". Well, every stone is different, their inclusions (杂质）are different too. While I'd love to go with a flawless stone, my wallet bags to differ. Learn how to balance the 4C is the key to make a killer deal.When I first talked with Bob, a G.G at whiteflash, he told me he had never bought anything above vs2 in his life. What's the difference, he said, you can't see the inclusion with your naked eyes. As a matter of fact, there is a lot of bargain hunters who follow the SI grades, even I grades, and they can find stones look flawless after being mounted. That's skill.

What I try to say here is that the type, and location of the inclusion make or break the deal. There are pinpoint, cloud, feather, crystal, black crystal, etc. What you need to remember is 3 tips here:

Tip #3: go with "eye-clean" stone. You better not see any inclusion from the top down.  Don't believe it when somebody says to you, "don't worry the prongs will cover the spot here." It's not always that easy to find the right setting with the right size prong. 

Tip #4: stay away from "black crystal" or "carbon". No matter how nice the stone is, a carbon could ruin it and make it worthless.

Tip #5: "Cloud" and "crystal" are tricky, be aware the location and size of it. 

BTW, I always start my search from vs2.

-- Color --

Watching appraiser grading the color was very unsettling for me. What they have is just a set of master stones, from GIA lab in this case,which represent each grade. Then they put your stone in a folded white paper, with 2 estimated master grades on each side and determine which grade is closer. The appraiser (who used to work at GIA) was talking and eating gum at the same time, probably spent no more than 2 seconds on the comparison. Is he really that skillful, it's all subjective.  

So how white, or yellow is your stone? You will get different answer from the reporr, or looking under different lighting. The one diamond I picked is graded G by GIA, but this appraiser said the lab is slacking off and this is definitely an E. Go figure. Other than telling you to see it yourself , again, you need to consider the following factors:

Tip #6 : Good cut elevates the color. Because white really is our way of saying brilliant and color- less. A good cut could make the stone sparkle so that you won't notice the real color. A lot of brand stones, such as A cut above from Whiteflash, claim on paper that their stones are 1 color grade higher than other stones.

Tip #7: Look at the stone under different lighting first, if you can , take it under broad day-light.

Tip #8 Stone with Fluorescence ( A blueish hue) can sometimes alter the yellowish color to look a lot whiter. But medium to strong fluorescence downgrades the overall quality and value of the stone, so you have to decide to look good, or better value.

I alwasy start with H, and work my way up.

--Cut---

A diamond is all about cut, and it is certainly the most fascinating part of my entire learning experience. We, as casual buyers, probably don't need to learn every bit of the details. However, we should always put Cut at No. 1 when evaluating the stone. Personally, I would only buy ideal cut even for small ones. In the long run, you will hold on to the ideal cut and get the best value out of your purchase. Whether to trade up, make it a side stone for your future upgrade, or simply reset, this diamond will not lose value and always be useful.

I will focus on round brilliant cut here since it's the most purchased shape. In the round cut world, it has become very popular to get a pattern look. You can see from these pictures and find (left to right)-- Hearts and Arrows, Eight Start, Solarsfera, Eighternity.

Although it's personal taste, the top jewelers like to push these patterns and somehow have made it a "must have" purchase. Among these patterns, hearts and arrows(H&A) is the most popular and avalable at every big name store.  You can read more in this article - Hearts and Arrows Guide. Cut is all about geometry. I admit that I am a sucker for H&A. How can you not be fascinated by these gorgeous idealscope image? The perfect symmetry, uniformality and cascading hearts and arrows, I love it!

There are simply too much to learn even with the latest technology, it requires experienced eyes to see the leakage, asymmetry and other flaws. I never believed that I would get the best stones, but only "better" ones. These are the tools and methods I use:

1. Sarin Report:  I showed an example in Carat, the report basically tells you the measurements for proportions. Pay special attention to the second column there. These are the digits labs used for grading. You should always ask for sarin report before buying any diamond. At the beginning of diamond industry, Marcel Tolkowsky wrote a paper and declared the very best cut proportions. But over the years, people realize that variation of TIC( Tolkowsky ideal cut) is as ideal, hence the range of proportion and the right combination of there measurements are further developed.

Tip#9: If your SA never heard of Sarin report, that's a flag right there.

2. Holloway Cut Adviser score:  According to this 大帅哥

An ideal cut diamonds should stay stay in a certain range of depth, table size, crown angle, pavillian angle and cutlet, and he developed a formular to generate a score indicating the quality of round cut stones. Here is the link to HCA caclulator. Just as the instruction says, you should stay with in a 0-2 HCA score to ensure an ideal cut.

Tip#10: Use Sarin report and HCA to see your stone fits in the ideal range.

3. Again, taste and preference play a huge role here. People like their stones shine in differet ways, and the industry use Brilliance, Fire and Scintillation to describe the visual effect. Brilliant Ideal Cut (BIC) and Fiery Ideal Cut(FIC) were further introduced to categorize 2 distinctive looks. To be honest, I can never intuitively pronouce BIC or FIC when looking at the stones. Only when the appraiser suggested either way, I started to realize- ain't that the truth? You probably shouldn't spent too much time on it either. Generally speaking, HCA will give you an image indicating where the score is on the overall scale, then use the 3 diagrams here to see where your stone is :

4. Idealscope - Holloway had also invented a tool called idealscope to allow direct viewing of light reflcection. These images will tell you the leakage, arrow and heart shape, symmetry and light return. A good diamond seller shoul be equiped with such reference, not sure if blueniles has it though.  

The discussion of the Cut could go on and on, you can find a lot of readings, thesis even, on the internet. My belief is Ideal cut, HCA score 1-1.5, no big leakage, arrows and hearts pretty even out. Excellent symmetry and polish, < thin girdle, < 0.5 cutlet, bigger table size,  and relatively small difference between min to max diameter.