First, determine your budget. One general rule of thumb when buying a diamond engagement ring is "two months' salary." This guideline was derived from a survey of engagement rings that were purchased over a two-year period compared to the buyer's annual income. This is just a guideline, it's not carved in stone and your first consideration should be what you can comfortably afford -- not what the diamond industry or a jeweler tells you.
Deciding on carat size is really about striking a balance between size and quality. If she prefers larger jewelry items, and you are working within a budget, you can still find a larger diamond of excellent quality gem by selecting one which is graded slightly lower in terms of color and clarity.
Men typically want a smaller diamond of higher quality. With the women “Larger is Better”. Your diamond salesperson will help you decide the largest size and best quality that satisfies both of you and meet your budget.
Think about what sort of setting will hold the diamond. You'll have to be sure that the setting you choose is made to fit the carat weight of your diamond.
Learn about the 4 C's of Diamonds before you begin shopping.
A certificate is a "blueprint" of a diamond, it tells you the diamond's exact measurements and weight, as well as the details of its cut and quality. It precisely points out all the individual characteristics of the stone. Certificates also serve as proof of the diamond's identity.
A certificate is not the same thing as an appraisal. A certificate describes the quality of a diamond, but it does not place a monetary value on the gem. An insurance appraisal places a monetary value on your diamond for obtaining insurance coverage.
There are many diamond labs that issue certificates, but the Gemological Institute of America (GIA) and the American Gem Society (AGS) are the two most widely regarded and recognized diamond grading labs in the world.
Shopping for certified diamonds allows you to make an informed choice about your selections, and to comparison shop. You can compare one diamond with a particular weight and quality with other diamonds of similar weight and quality to determine which is the better value.
Even with all this information that is on a Diamond Grading Report, it DOES NOT tell you how pretty the diamond is or how much it sparkles. Only your eyes can see the beauty in a diamond. Think about this, you can read the menu at a restaurant about a certain entrée, but it doesn’t tell you how good tastes.
NOTE: If a jewelry store offers to sell you a loose diamond without a certificate, keep in mind that it means you are buying the diamond based only on the salesperson's claim about its quality and that a trained gemologist like Michael or even other jewelers may disagree with the salesperson's assessment.