Obstruction versus leakage

[Dreamer_D]

Just for my own edifiction...

What is the difference? What angle combos suggest each one is a problem? What would the IS images look like for each?

Thanks.

 

[kenny]

Obstruction is when light can't get into the top of a diamond because your head is in the way.
Your head obstructs the light.

Leakage is when light leaks out the bottom or side of a diamond instead of being reflected back out the top.

 

[Dreamer_D]

Date: 2/7/2010 5:36:07 PM
Author: kenny
Obstruction is when light can''t get into the top of a diamond because your head is in the way.
Your head obstructs the light.

Leakage is when light leaks out the bottom or side of a diamond instead of being reflected back out the top.

Kenny, thanks. I think I knew this difference in the cause of the poor optics, but I am not certain what types of cutting combos might result in one or the other, or what the two might look like in IS images. I ask because I have read it threads that one was a problem more than the other, and I wondered what it was in a particular angle combo that made this so, or how it was recognized in an IS.

 

[Garry H (Cut Nut)]

You can get a bit of help from this chart
http://www.ideal-scope.com/1.using_reference_chart.asp

What is worse?
For me it is leakage because I believe that when there is some leakage there will be more when the stone is dirty, whereas obstruction goes away when you tilt the diamond - and those areas that go from dark to bright tend to be some of the best contrast you will see.

 

[yssie]

I believe when you''re using your is the light is coming from the pavilion and is reflected off the red film on the inside of the IS onto the diamond crown/table, so leakage will be the colour of the light you''re using (white, usually), areas of reflected light will be red, and obstructed areas (where your head is) will be black

 

[Lorelei]

Date: 2/8/2010 12:21:23 AM
Author: dreamer_dachsie

Date: 2/7/2010 5:36:07 PM
Author: kenny
Obstruction is when light can't get into the top of a diamond because your head is in the way.
Your head obstructs the light.

Leakage is when light leaks out the bottom or side of a diamond instead of being reflected back out the top.

Kenny, thanks. I think I knew this difference in the cause of the poor optics, but I am not certain what types of cutting combos might result in one or the other, or what the two might look like in IS images. I ask because I have read it threads that one was a problem more than the other, and I wondered what it was in a particular angle combo that made this so, or how it was recognized in an IS.

Hi Dreamer

As a general rule, these are the proportions I look out for concerning each. Steep deep combos can show leakage ( CA >35/ PA >41) or steep pavilioned diamonds ( PA > 41.4 as a guideline but take each stone as an individual as some with 41.2 pavilion angles can show leakage even with a correspondingly shallower crown), shallow pavilioned stones ( pavilion angles < 40.6) and shallow / shallow angle combos ( random example; CA 32/ PA 40.2) can show obstruction. I tend to be on the lookout for obstruction particularly with GIA rounding at angle combos of 34/ 40.6 or less, rounding issues can mean some borderline combos such as 34/ 40.6 definitely need evaluation with images. Also longer lower girdle facets can help lessen leakage or obstruction in some cases ( 80% or above can sometimes help), also overall cut precision can play a part, but again an Idealscope image is needed in order to judge.

I will try to find some IS examples for you or other images, but this thread has some steep deep IS examples in Idealscope and photos,

http://journal.pricescope.com/Articles/72/1/Laboratory-Cut-Grades-What-the-report-doesn’t-show.aspx

With the link Garry posted, http://www.ideal-scope.com/1.using_reference_chart.asp

look at the IS image titled very shallow. You can see the dark ring around the table where the light is blocked and also if you look at the arrow tips, notice they look like paddles? This is also due to obstruction.

Recent thread on obstruction,

https://www.pricescope.com/community/threads/obstruction.129821/

Video made by Garry bottom right of the page titled Head Obstruction,

http://diamondscope.pricescope.com/