A ring is a never ending circle that symbolizes permanence. When proposing marriage, this represents a never ending circle of love and admiration for someone.
And what better ornament for the symbol of your lasting love than a beloved stone reputed to last forever, a diamond? But before you purchase a diamond ring, you'll have to figure out just what kind of diamond best suits the person you're buying it for and estimate potential diamonds and settings.
Select the Right Cut
Select a cut that maximizes shine and beauty. The cut of a diamond will determine how the stone redirects light, causing it to glitter. Many consider this to be the most significant feature of a diamond ring. Even an overpriced diamond, if cut poorly, can look lackluster.
The main categories of cut are:
Ideal cut (sometimes called "Excellent"), shows the lightest possible back to your eyes, making the diamond sparkle brightly.
Very good cut indicates slightly less light back to your eyes than an ideal cut.
Good cut displays most of the light that enters the diamond back to your eyes.
The fair cut reflects noticeably less light than a good cut but is usually considered to still be a quality gemstone.
Be Informed About Diamond Color
Equip yourself with information about diamond color. When a diamond seller talks about the color of a diamond, they're really referring to its lack of color. Diamonds are being rated on a scale that goes from D to Z. Diamonds that are perfectly white are the most alluring/expensive and are ranked at D.
Color grades can be minutely distinct from each other. Choosing a diamond with a unnoticeably lower color grade can save you a significant amount of money.
Ranks F to E will only have minimum shades of color that can only be detected by an expert gemologist.
Ranks H to G are almost transparent. The separation between these and higher color grade diamonds will only be obvious when compared side by side.
Ranks J to I will usually have a detectable warmth to their color tone, usually in the form of yellowness, but are still considered to be near transparent.
Ranks worse than I will have outstanding yellow tones coloring the gem.
Choose Perfect Purity
Identify your ideal purity. Even the most expensive diamonds will likely have minute flaws and defects. Gem experts name these "inclusions." For high - quality diamonds, these inclusions may only be visible under a microscope. But, too many flaws or the wrong kinds of flaws can make your diamond cloudy.
Clarity grades, from perfect to visible flawed, are rated: FL (flawless), IF (internally flawed), VVS1, VVS2 (very, very slightly included), VS1, VS2 (very slightly included), SI1, SI2 (slightly included), and I1 (included).
You might save some money by picking an SI1 clarity diamond. These often only have flaws visible under magnification, making them a more reasonable purchase without looking cheap.
Before purchasing a diamond with an SI rank or worse, prove with the seller that the diamond is "eye clean." This means there are no flaws evident to the naked eye.
Fluorescence Does Matter
You should take fluorescence into account. Little amounts of boron are frequently trapped in diamonds, causing a slightly milky appearance in the stone. This is named "fluorescence," and it is rated from Faint to Very Strong.
If you are not able to judge a diamond in natural light to ensure there is no milkiness, you should avoid Strong or Very Strong fluorescent stones.
Look at the Diamond from above
View possible diamonds from above. Looking at your diamond from above will give you a better conception of how the stone will look when placed in a setting. While most people judge the size of a diamond by karat weight (CTW), this can be deceptive. Even small diamonds that have been cut correctly can seem sizable.
You'll also want to look at potential diamonds in many various kinds of lighting. Some stones look stunning in bright light but lose their appeal in everyday lighting.
Carat total weight (CTW) is the weight of all the diamonds in the ring, containing side stones.
When only the CTW is listed, ask the diamond seller about the condition and weight of the centerpiece stone. If the seller does not want to give this information, this is probably a sign that the diamond is low quality.
Special Diamond Shape
Pick the best shape of your diamond. The shape of your diamond will highlight various features. Round brilliant cuts will bring out the sparkle in your diamond. Step cut diamonds, like Asscher and emerald cuts, will display flashes of light as opposed to sparkle. Longer shapes, like an oval, pear, and marquise cuts, can be proper for longer fingers. Some other shapes for your thinking:
Diamond Must Be Certified
Check if the diamond is certified. You'll want your diamond to have been graded by an independent expert so you know you're really getting what you're paying for. This is also recognized as a certificate and will include an evaluation of cut, clarity, color, carat weight, light behavior, apart from giving other measurements such as fluorescence, proportions, alignment, symmetry, and fingerprint. 
Diamond grades can differ from one lab to another, and also from one gemologist to another. This is due to certain shortfalls of the human eye, apart from other honor issues. Note that the price of the diamond changes based on the diamond grade. There have been many diamond grading scams because of such prejudiced grading practices.