I tried to read through the entire thread and there's lots of good advice...
I spent way too much time learning about diamonds and don't really suggest going as far as I did. Just make sure you buy from a reputable place, there's a certificate and have a 3rd party appraisal depending on how much your spending.
I would also suggest going to a Jewelery Exchange where's there's lots of stores in one spot as they have the best deals. I will also suggest looking at and buying loose stones.
Furhtermore, looking at a stone under a microscope it utterly useless in my mind. You want to have a good cut, clarity and so on but as long as the stone really sparkles and looks good by eye is all that matters. Everyone will be looking at the ring/stone with eyes not microscopes.
My jeweler had suggested to me what to get, she also had pulled stones that I had requessted and had various size stones and quality there for me and just let me look at them. I did so by eye and then with the magniying thing. She asked me what I thought of each one and then we grouped them in order and went through them together. She actually showed me where I could save money and only loose quality that a trained eye would notice. I was impressed.
Ultimately I stuck to my intial standards (for the most part) and bought a diamond by quality and brilliance (how well it sparkled) compared to getting a slightly larger one. I was lucky my wife only wanted a .5 carat but being bigshot (sure) I upped it to a .73 carat set in platinum. Apparently white gold can discolour and turn more gold color in time?? Not sure, I liked the color of platinum better regardless but d@mn it's pricey.
As we were both talking about getting married so much and we knew we wanted to get married at a certain time. I was able to have me wife there for most of the buying experiece so we both got to enjoy it and she got exactly what she wanted. In hindsight, I probably should have done a pre-proposal before the ring shopping but whatever...she was happy.
Lastly, there was a saying along the lines of as a diamond ages it shrinks...well it's actually the finger it's on usually gets bigger so the diamond just looks smaller
Hopefully this is your first and last engagment ring, do it right and get something you both will be happy with for years to come. And like others have said, hopefully one day someone else new to the family will be able to wear it with pride as well.
Congratulations.
