Is this safe to buy?

[Boloh]

Hi all,

I came across a diamond that failed the Holloway Cut Advisor for girdle thickness. Specifically, the Cut Advisor displayed the following message:

"The total depth % you entered suggests the girdle is dangerously thin, or the data you entered is incorrect"

However, the diamond's girdle is 'Slightly Thick -> Thick'. So my question is, since the Cut Advisor does not take girdle info as an input parameter, AND since the diamond's girdle thickness is on the slightly thicker side, would it be safe to get this diamond?

Here's the diamond's spec:
Clarity - VS2
Colour - D
Cut - Ideal
Symmetry - Very Good
Depth - 61.7%
Table - 54.8%
Crown Angle - 33.8 %
Pavillion Angle - 43.0 %
Culet - Very Small
Fluorescence - Strong
Girdle - Slightly Thick to Thick
Measurements - 6.99 x 6.91 x 4.30 mm

Thanks for the help!!!!

 

[Lord Summerisle]

first thing i can think of - is the pavilion depth you''ve entered actually 43° or 43% ? it will make a differance (and 43° is awfully steep for a pavilion)

some certs are confusing in that they list the crown angle, but a pavilion depth %

if you run the HCA with 33.8° crown and 43% depth you get a score of 0.8

 

[Boloh]

Hi,

You''re absolutely right! I did get the spec down wrong exactly because of the confusing % vs degree that they use at various places.

Here''s the updated spec:

Here''s the diamond''s spec:
Clarity - VS2
Colour - D
Cut - Ideal
Symmetry - Very Good
Depth - 61.7%
Table - 54.8%
Crown - 15% (33.8 degrees)
Pavillion - 43% (41.1 degrees)
Culet - Very Small
Fluorescence - Strong
Girdle - Slightly Thick to Thick
Measurements - 6.99 x 6.91 x 4.30 mm


Now, using the revised (and correct) spec above, I notice something strange with the Cut Advisor.

I noticed that I get different HCA rating depending on whether I use % or degrees (or mix of them) for the Crown and Pavillion as follows:
Crown 15%, Pav 43% -> 1.3 Excellent
Crown 15%, Pav 41.1 degrees -> 1.9 Excellent
Crown 33.8 degrees, Pav 43% -> 1.3 Excellent
Crown 33.8 degeres, Pav 41.1 degrees -> 2.0 Very Good

As you can see, the different combination yields different HCA rating, and they vary quite largely. Should this ever happen?

Thanks,
Paul

 

[Lord Summerisle]

yes, perfectly normal.


from a link within the HCA screen explains this.

It is best to input crown and pavilion angles into HCA to reject less beautiful diamonds. We use trigonometry to calculate the angles from % data. Use angles if you have them because:
%''s are often rounded i.e. 13.3% crown height becomes 13% or 13.5%.
Pavilion depth % when converted to pavilion angle often understates the pavilion angle by 0.15°
Scanners are not good at measuring culets; a culet reduces the pavilion depth % but does not change the pavilion angle.
Sarin scanner data is better than Ogi because they calculate the angles and then scale of the %''s. Ogi works the other way round.

If you only have access to % info (e.g. EGL, IGI or HRD report) then use the %''s to reject known duds, then and ask the supplier to run Sarin angle data on your short list.

If the supplier has idealscope photos or GemAdviser files of the diamond, then they are more useful than HCA.

 

[Boloh]

Would you recommend this diamond? It's selling for roughly $9,750 (CDN and US roughly similar in currency value at the moment).

Also, is there a noticeable difference between an HCA Excellent (< 2.0) vs Very Good (~2.0) ? Excellent is obviously better, but is Very Good that much worse?

Thanks,
Paul

 

[Lord Summerisle]

difficult to answer - personally, it falls outside what i would buy unseen off the net... but if you''ve seen it in person, and like it...then go for it.

A quick search on here shows there are similar stones for similar price... not exact...
have a look at for starters
1.22 D VS2
1.26 E VS2

 

[Linda74]

What is the diamond''s carat weight??

 

[Boloh]

The diamond''s weight is 1.28 carat. And yes I did see it in person and it looked great.

The catch is that it has strong fluorescence. I''ve read that Very Strong fluorescence diamonds should be avoided like the plague. What about for Strong? Would it look murky under sunlight? If it''s a clean glow in dark settings like a discotheque then I can live with that.

 

[Lord Summerisle]

theres only one way to know how it will look in certain lighting conditions... and thats to see it: so might be an idea to talk very nicely to the vendor and see if they will let you view the diamond in sunlight.

this page may be of use: here

 

[Boloh]

Thank you very much. I think I will try that tomorrow.