0.7G or bigger?

[confusedintoronto]

Just stumbled onto this forum few days ago while looking at engagement rings and I think you all do a fantastic job helping each other out. My question has probably been asked many times already. I've been looking at getting my girlfriend a pave style ring with a canadian GIA certified round diamond. My budget is around $5k. I have a jeweller offering me:
0.7 G Ex VS1 and a 0.7 D Ex VS2 for $100 more. They look great but I know I can get a 0.8 H colour Ex SI in that range as well.

I found out through that my girlfriend really liked this style from birks but it was a 1 carat HI colour I for $7000 which is over my budget. Should I consider the 0.7 or go bigger while compromising colour and clarity. The jeweller said this is the very best I can get and I want to make sure I won't regret it later if it is better to go bigger.

Thanks a ton

- So very confused.

 

[ebadevil]

when I get home, I'll post a mini study that I did on carat weight vs size (diameter) of a diamond. You gotta remember, carats are a measure of weight rather than "size". There is a good correlation between weight and "size", but different diamonds are cut differently. A fairly vertical diamond might seem smaller from the top than a fairly flat diamond.

What you are asking for is marginal utility of the price vs size increase. If you remember basic economics, in the beginning, you get a very large utility (diamond size) increase from a small price (carat weight in this case, but $$ could also be substituted) increase. As you keep increasing price, your marginal utility (size) decreases. Based on my analysis of the derivatives of the carat vs diameter model at different points (and again, I don't have this in front of me), you get pretty good return up to about 1.3 carats, after which it starts slowing down. I believe it becomes inefficient after about 1.5 carats.

So your "efficient" size of a diamond is probably somewhere in the 1.3-1.5 range, although you get a lot of "value" up to 1 carat. The weakness of the model is that it looks at weight vs diameter, rather than $$ vs diameter. Although, between not having enough time to collect enough $$ data to make the model work, and the fact that the diamond market is so price inefficient, that's a much more difficult task. Assuming that there is a "unit diamond price" somewhere out there, a weight vs diameter model is satisfactory.

Based on this, I would advise to forego some or the lesser C's in order to get some "size utility". Don't skimp over on cut though. Take this advice with a grain of salt. My diamond background is rather small. I do finance/economics/math, so this is purely based on my "size efficiency" model

Don't forget though, everything has opportunity cost. Going up in size, sacrifices C's. At some point, sacrificing C's also becomes inefficient in order to gain size. It's a balance. But since the C's price is a lot more linear than weight/size price, there is definitely a certain amount of C's you can sacrifice with little "value" reduction in order to gain quite a bit of size value.

My 2 cents here...

PS I'll post the graph when I get back home today

 

[Gypsy]

You should go down in color and clarity. ANd yes, go up in size.

But you must understand. CUT is what matters:

The entire purpose of faceting a diamond is to reflect light.
How well or how poorly a diamond does this determines how beautiful it is.
How well a diamond performs is determined by the angles and cutting. This is why we say cut is king.
No other factor: not color, not clarity has as much of an impact on the appearance of a diamond as its cut. An ideal H will out white a poorly cut F. And GIA Ex is not enough. And you must stick to GIA and AGS only. EGL is a bad option: [URL='https://www.pricescope.com/community/threads/egl-certification-are-any-of-them-ok.142863/']https://www.pricescope.com/community/threads/egl-certification-are-any-of-them-ok.142863/[/URL]
So how to we ensure that we have the right angles and cutting to get the light performance we want?
https://www.pricescope.com/wiki/diamonds/diamond-cut
Well one method is to start with a GIA Ex, and then apply the HCA to it. YOU DO NOT USE HCA for AGS0 stones.
https://www.pricescope.com/wiki/diamonds/holloway-cut-advisor
The HCA is a rejection tool. Not a selection tool. It uses 4 data points to make a rudimentary call on how the diamond may perform.
If the diamond passes then you know that you are in the right zone in terms of angles for light performance. Under 2 is a pass. Under 2.5-2.1 is a maybe. 2.6 and over is a no. No score 2 and under is better than any other.
Is that enough? Not really.
So what you need is a way to check actual light performance of your actual stone.
That's what an idealscope image does. https://www.pricescope.com/wiki/diamonds/firescope-idealscope
It shows you how and wear your diamond is reflecting light, how well it is going at it, and where you are losing light return. That is why you won't see us recommending Blue Nile, as they do not provide idealscope images for their diamonds. BGD, James Allen, GOG, HPD, ERD and WF do.

The Idealscope is the 'selection tool'. Not the HCA.
So yes, with a GIA stone you need the idealscope images. Or you can buy an idealscope yourself and take it in to the jeweler you are working with to check the stones yourself. Or if you have a good return policy (full refund minimum 7 days) then you can buy the idealscope, buy the stone, and do it at home.


Now if you want to skip all that... stick to AGS0 stones and then all you have to do is pick color and clarity and you know you have a great performing diamond. Because AGS has already done the checking for you. That's why they trade at a premium.

 

[TC1987]

In that size range, an H will look about as white as a G.

3/4ct is about 5.8-5.9mm diameter, .8ct is about 6mm. and 1ct is about 6.4-6.5mm diameter.

1.25ct is about 7mm, you have to go to about 1.6ct to hit the 7.5mm diameter in a modern RB.

Face-up size is the area of a circle.

[URL='https://www.pricescope.com/forum/files/upgrades1.jpg']https://www.pricescope.com/forum/files/upgrades1.jpg[/URL]
^

top ring is my original diamond at 1 ct and 6.5mm, anniversary ring at 1.58 cts and 7.45mm, and my new AVR diamond at 2.12 cts. and 8.15mm

Those aren't mine. They are from this thread: [URL='https://www.pricescope.com/community/threads/original-e-rings-and-upgrades-comparing-diamond-sizes.188110/']https://www.pricescope.com/community/threads/original-e-rings-and-upgrades-comparing-diamond-sizes.188110/[/URL]

 

[TC1987]

My computer was about to reboot, so I had to wrap that ^ up. But I was going to say: If she wants 1ct, a "light" ct is .9ct or so and is 6.3mm or so and will look "1 carat" to the eye. Staying under the 1ct mark will save money.

Color: I do not advocate going as low as J unless you know that she likes that much tint. G and H are still very white in the 1ct and under range. You could possibly look at I, especially an I with strong blue fluorescence. The I color range is where most people can start to see tint enough that it might bother them a little, unless they are very color sensitive. Strong blue will help cancel out that slight vanilla tone in I at least whenever UV light is present.

 

[confusedintoronto]

Thanks for all the replies so far. I was told the size difference between 0.7 and 0.8 is barely noticeable. The price of the 0.8 H colour SI2 is around $400 less than a 0.7 G colour VS1 and around $500 less than a 0.7 D colour VS2. All three are GIA certified Excellent cut. Just wondering if I should pay the $400 extra for a better quality diamond or save the $400 and go with a size that doesnt look a whole lot bigger. Would the 0.7 look/sparkle better or look bigger overall because of the higher colour/clarity?

Thanks again everyone.