Trying to understand how changes in angles/% affect a RB diamond

[puravida]

I went through the diamond tutorial again but didn''t find anything to answer my questions about how changing a diamond parameter affects what the stone looks like.

From what I read, I found that for RBs, the table should be within 55-58%. Smaller tables wil show more fire. I''m not sure if that means on the smaller end of the ideal range, or smaller than 55%.

For RBs, how does the appearance and performance change as the:

-crown angle increases/decreases

-crown height % increases/decreases

-pavillion depth increases/decreases

Thanks.

 

[stone-cold11]

Check through the journal articles.

This article.

http://journal.pricescope.com/Articles/72/1/Laboratory-Cut-Grades-What-the-report-doesn%E2%80%99t-show.aspx

Image from this article.
http://journal.pricescope.com/Articles/37/1/GIA-Excellent-Cut-Grade-Case-Study.aspx

 

[puravida]

Not sure I understand.

So if crown angle increases, do does pavillion angle. But how does that affect how the diamond looks?

I didn''t see anything in that article about how changing one factor affects another and how that overall changes how a diamond appears.

In the link you posted, #2 and #6 look the best. Am I right?

 

[Garry H (Cut Nut)]

Try this
http://www.diamond-cut.com.au/03_inverse_relationship.htm

 

[Lorelei]

Date: 1/15/2010 12:32:22 AM
Author: Garry H (Cut Nut)
Try this
http://www.diamond-cut.com.au/03_inverse_relationship.htm

Thats a great link Garry posted and should help you.

Also concerning the crown and pavilion angles and visible effects on the diamond, this is a basic guide.

A small table can influence fire, particularly if coupled with a steeper crown angle > 35.5 degrees. This crown angle normally needs a shallower pavilion angle usually no more than 40.6 degrees and are often referred to as fiery ideal cuts ( FIC). Sometimes due to this proportion configuration, some extra physical depth can be seen which can make a diamond look a little small for the weight. FIC's have their fans and that these types of stones can be a bit small for the weight is a trade off they are willing to make.

A shallower crown angle can help increase white light or brilliance and especially teamed with a larger table- a shallower crown angle in PS terms is in the region of < 34 degrees. These are often called brilliant ideal cuts ( BIC). It is important to keep pavilion angles steeper to balance the shallower crown angle, otherwise what is called obstruction can take place. This is visible darkening of the stone when viewed closely due to the shadow of the viewer's head/ body blocking the light to the diamond. So it is best to keep pavilion angles around 40.6- 41 degrees in these cases and always check with an Idealscope image especially due to GIA rounding issues, an Idealscope image will show if obstruction will affect a particular diamond. Also stones with crown angles of 32.5 degrees or less coupled with a very thin girdle need careful checking by a trusted expert to make sure the diamond is not at increased risk of chipping due to the crown angle/ girdle combo.

Once a pavilion angle gets much past 41 degrees, then light leakage can sometimes be seen, even if the crown angle is shallower to compensate for the pavilion angle. Apart from light leakage, other undesirable issues can arise such as colour entrapment ( a near colourless diamond can look less white or hold more warmth than one with a less steep pavilion or better cut) and these stones will look worse when dirty.


Then we have what we refer to as the steep deeps. These are those diamonds which have steep and deep crown and pavilion angles, the cliff edge is around 35 CA/ 41 PA. These stones require Idealscope images to check for light leakage ( where light escapes from the diamond instead of being reflected back to the eye). Such diamonds with steep deep angle combos will often show light leakage in Idealscope image, a dark ring around the table to the eye when viewing the diamond, also these diamonds can be dull and lacklustre due to the light escaping. In extreme cases, with loose diamonds with steep deep angles held between the fingers when unset, it is possible to even see skin showing through the stone. These diamonds also often look worse when dirty.

You will find out of the diamond types mentioned, the near Tolkowsky Ideal Cuts are popular here, those have crown angles which usually fall between 32.5- 35.5 degrees along with a complimentary pavilion angle. These can offer a good balance of fire and brilliance which many diamond buyers want.


Cliff's notes on angles - FIC, BIC and TIC from Garry's website below. The Holloway Cut Advisor will also tell you which type of diamond it is such as BIC, FIC, TIC.

http://www.diamond-cut.com.au/23_bicfic.htm


Hope this helps!

 

[puravida]

Thanks for last two posts, looks like the advice I was looking for. I''m on my way to work now but will remember to study these later

 

[Lorelei]

Date: 1/15/2010 8:04:12 AM
Author: puravida
Thanks for last two posts, looks like the advice I was looking for. I''m on my way to work now but will remember to study these later

Very glad to be of help to you, just ask if you have any more questions!