Ok, diamonds..
Here is my recommendation.
Do not buy Tiffany's. You will be spending 45% of the value of the diamond on a little blue box.
Buy a diamond, then have it mounted.
Ok, here is what I did, you can make adjustments according to budget.
There are four things to know about diamonds, cut, clarity, carat, color.
Colors are based on letters, top tier being, D, E, F.
Second tier being, G, H.
I wouldn't go lower than H for color and in my opinion, F-G stones are the best value to quality. Lean towards F if you can find one.
Cut, You know, Princess, good choice... Very popular.
Clarity, There are lots of opinions on this, but here is my advice. Clarity means, how many dirt molecules you can see in the stone. Some you can see with the naked eye, other molecules you need magnification to see. It is my opinion, that buying a stone that has a clarity value higher than "visible to the "naked eye"" is a waste. VS2 or VS1 is in my opinion, the way to go. Yes, there are "inclusions" but you need a microscope to see them. And if any of your wife's friends are walking around with microscopes, looking for inclusions, they deserve to be punted in the head.
So the last thing is ct. Well, that's budget. But understand, a 2 ct. diamond is not twice the price of a 1 ct. diamond. It's much more, as Laura said.
So lets recap:
1) Don't buy street level diamonds (retail stores at malls, etc. go to a diamond wholesaler, pick stone and have mounted.)
2) In my opinion, the BEST price/grade value will look something like this:
F-G color
Very Slightly Included (VS1 or VS2)
at highest ct. weight you want to spend.
You also want a stone that is GRADED, by GIA. (lets call it a certification and serial number).
There are some other things to consider like girdle, depth, etc. But they are less important.
Some other things to keep in mind, you can find a 1.5ct. diamond that looks bigger than a 2ct. diamond, depending on the way they look. Diamonds have a life of their own, you really need to look at them. Just cause it looks good on paper, doesn't mean it will look good in your hand.
Try to find a wholesaler who will get you 3-4 diamonds to look at. Then you can compare them to one another.
Also,
www.pricescope.com is a good resource for finding diamond values, vendors, etc.
Email me if you want some names of people to call. I don't vogue for anyone in terms of absolute confidence, etc. Like buying a car, I can send you to a dealer, salesman, but you need to do your homework. Their objective will to always be, maximize the value of the sale, and your objective should be, to get the best price. Which means, you need to do leg work.