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What mm change is noticeable?

carolinenc

Rough_Rock
Joined
May 5, 2009
Messages
36
I currently have a 2.02 carat RB that is 8.26mm x 8.29 mm. I'm looking to upgrade mainly for cut and maybe for color. I'm trying to decide what range of sizes I should be looking at to keep the same look. For instance, I assume going down to 1.9 ct might be a good idea to get better value but still appear the same.

I'm also considering resetting this stone into a VC Emilya (although that is undecided), so if I did that I wonder what size I could go down to without noticing the diamond was smaller?
 

Gypsy

Super_Ideal_Rock
Joined
Aug 8, 2005
Messages
40,225
Without a halo even an 8mm stone will look smaller. With a halo, I think you can probably by with a 7.8mm stone.

Remember, compare dimensions not weight.
 

AdaBeta27

Brilliant_Rock
Premium
Joined
Sep 7, 2004
Messages
972
area = pi * (diameter^2) 4 Square mm area of a circle.

Set up a spreadsheet and you can plug in various diameters and calculate a % change in face-up size (surface area) compared to your original diamond. The adage on PS is that a 10% increase in surface area is worth upgrading to. But you are asking the question "Will I notice the size change?" This graphic http://www.arihantdiamondinstitute.com/images/diamond_carat_size_scale.gif has an 8.2mm, and 7.8mm and 7.4mm.
 

kenny

Super_Ideal_Rock
Premium
Joined
Apr 30, 2005
Messages
31,568
This topic tickles my brain, because it is not real, as in out there in the real world.
What is out there in the real world is the math that describes the area of a circle.
So I see this thread's subject line as just brain tickling. :bigsmile:

OP, my post is not criticizing you personally.
I've read PS over 10 years and this topic come up constantly.
We pay dearly for weight so struggling with how much we should pay for is totally reasonable.

...

Let's assume that the so-called PS 10% rule is true, that the diameter difference must be 10% for us to see the size difference.
Let's start with a well-cut round with a diameter of 6.4 mm.
A round that is 10% smaller would have a diameter of 5.76 mm.

So, it could be argued that anyone who bought a 6.4 mm wasted money. (as in paid for something you can't see)

BUT! ...

A 5.18 mm round would be 10% smaller than that 5.76 mm.
So, anyone who bought a 5.76 wasted money.


BUT! ...

A 4.66 mm is 10% smaller than a 5.18 mm.
So, anyone who bought a 5.18 mm wasted money.

... and so on.

So, IMO the argument for not paying for a particular size because a slightly smaller one looks the same does not hold water.

The only time it does make sense to buy a smaller diamond (to everyone in a concrete and absolute way) is buying a 0.98 ct. instead of a 1.00 ct.
But then it could be argued the 0.98 does not give a person the weight-mid-cleaness that a buyer gets from a full 1.0 ct.

IOW, all this stuff is not absolute.
For some reason we use mind games to justify buying whatever we buy.
Since such 'justification' falls flat why use it?
Just buy what you want to buy.
You don't need to engage in mind game faux justification.
If you must have a 'justification' here it is: "I bought this because I wanted it. Period."
This comes from a place of self confidence rather than insecurity.

If you could somehow replace the the hands with minds this all reminds me of that Escher drawing that makes us ponder what is real vs. what we make up.

screen_shot_2015-12-29_at_10.png
 

gm89uk

Brilliant_Rock
Premium
Joined
May 26, 2015
Messages
1,491
Hi Kenny,

Just a correction, a 10% change in surface area does not equal a 10% change in diameter due to the quadratic relationship between radius and surface area.

A 5.76mm has a 19% smaller surface area than a 6.4. 10% smaller surface area of a 6.4 is actually 6.07mm.

Also the rule is only with the original stone relative to the other. It is only about a 10% difference between two measurements, you can't keep going 10% more because then the difference is well and truly more than 10% surface area.

To answer the OP, based on the 10% rule you would aim for a diameter of 7.85 or above to not notice a difference.
 

kenny

Super_Ideal_Rock
Premium
Joined
Apr 30, 2005
Messages
31,568
gm89uk|1451417295|3967974 said:
Hi Kenny,

Just a correction, a 10% change in surface area does not equal a 10% change in diameter due to the quadratic relationship between radius and surface area.

A 5.76mm has a 19% smaller surface area than a 6.4. 10% smaller surface area of a 6.4 is actually 6.07mm.

Also the rule is only with the original stone relative to the other. It is only about a 10% difference between two measurements, you can't keep going 10% more because then the difference is well and truly more than 10% surface area.

To answer the OP, based on the 10% rule you would aim for a diameter of 7.85 or above to not notice a difference.

Thanks.
I'm not arguing with the accuracy of your post because the math does not in any way change the point of my post.
Many aspects of our buying decisions are all in our heads, while we like to think they are not.
 
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