Dirty, greasy diamonds

[FB.]

Most diamonds have to live with a substantial layer of grease and dirt on them.
It has been mentioned that the critical angles of diamond light handling change once the stone is dirty.

Are there certain diamond shapes (e.g. pear, princess) that tend to suffer more from being dirty?

Are there certain ranges of angles in round brilliants that are less affected (or more affected) by grease and dirt?

Thanks,

 

[AprilBaby]

I HATE when I see someone with a beautiful diamond all gunked up with soap and stuff!

 

[Lorelei]

Date: 11/20/2009 7:47:51 PM
Author:FB.
Most diamonds have to live with a substantial layer of grease and dirt on them.
It has been mentioned that the critical angles of diamond light handling change once the stone is dirty.

Are there certain diamond shapes (e.g. pear, princess) that tend to suffer more from being dirty?

Are there certain ranges of angles in round brilliants that are less affected (or more affected) by grease and dirt?

Thanks,

Steep deeps and steep pavilioned stones are more susceptible to go flat with dirt and grease.

 

[Garry H (Cut Nut)]

It is one of the reasons I have always favored slightly shallower proportions (and get a lot of stick for it) on HCA.

 

[FB.]

Garry & Lorelei

Can you elaborate a bit?
Steep/deep and shallow stones often share similar pavilion angles - around 41''. Or is it also due to the interaction between crown and pavilion.

Your statements would lead me to believe that something close to a 60/60, 33/41 would have both good angles for light handling, but would also manage to perform quite well when dirty.

Which of the following proportion sets (with incremental changes in crown and pavilion) would suffer least or most?


37.0/40.2, 36.0/39.8, 35.0/39.4


34.5/40.8, 33.5/40.4, 32.5/40.0


33.0/41.2, 32.0/40.8, 31.0/40.4


30.0/42.0, 29.0/41.6, 28.0/41.5

Thanks,

 

[Lorelei]

Date: 11/21/2009 7:01:35 AM
Author: FB.
Garry & Lorelei

Can you elaborate a bit?
Steep/deep and shallow stones often share similar pavilion angles - around 41'. Or is it also due to the interaction between crown and pavilion.

Your statements would lead me to believe that something close to a 60/60, 33/41 would have both good angles for light handling, but would also manage to perform quite well when dirty.

Which of the following proportion sets (with incremental changes in crown and pavilion) would suffer least or most?


37.0/40.2, 36.0/39.8, 35.0/39.4


34.5/40.8, 33.5/40.4, 32.5/40.0


33.0/41.2, 32.0/40.8, 31.0/40.4


30.0/42.0, 29.0/41.6, 28.0/41.5

Thanks,

Steep deep to me begins at 35/41 actual angled and above
Steep pavilion - above 41.2

* but* this does depend on angle averages and cut precision, so these are a general guideline. See what Garry says as his input is invaluable.

 

[FB.]

What about a 34.0/40.0?

But I though that the "obstruction" thread cast doubts on shallow-pavilion stones?

Or, if we want a stone that continues to do well when dirty, do we have to accept some obstruction?
On the other hand, a 33.0/41.0 would easily manage a shallow overall depth around 60% (and qualify as a shallow stone), but the pavilion is borderline deep, when we compare with steep/deep.

 

[Lorelei]

Date: 11/21/2009 7:17:45 AM
Author: FB.

What about a 34.0/40.0?

But I though that the 'obstruction' thread cast doubts on shallow-pavilion stones?

Or, if we want a stone that continues to do well when dirty, do we have to accept some obstruction?
On the other hand, a 33.0/41.0 would easily manage a shallow overall depth around 60% (and qualify as a shallow stone), but the pavilion is borderline deep, when we compare with steep/deep.

34/40 is a shallow shallow so will have its own issues as you know, dirt or grease could enhance the effect. Garry as you are aware prefers shallower proportioned stones as they are less prone to this effect but I can't remember exactly what proportion sets he prefers for these as to how shallow, I don't think they are as shallow to be at much risk of obstruction. 33/41 could be a good balance, geared more towards brilliance than fire but probably less susceptible to the effects of dirt.

I tend to think of shallow in two separate ways, the very shallow depthed and the shallow angled, these don't always go together.

 

[stone-cold11]

I would guess Garry prefers the angles where HCA scores around 0?

 

[Laila619]

Something like c 34 / p 40.6 with a depth of 60.6 % I'm betting.

 

[Garry H (Cut Nut)]

I prefer diamonds slightly shallow - say P40.5 C34.5 because that makes any ills not a problem (with hi symmetry you can go to a steeper deeper - often up to 35/41 - with tables below 60% for under half carat and reducing as the diamond size increases to say under 58% above 1ct.

As for the variations - use this rule - if tolkowsky is perfect then use the 5:1 rule:

for every plus 1 degree crown subtract 0.2 degrees from the pavilion
for every minus 1 degree crown add 0.2 degrees to the pavilion

This works well from 32 to 37 crown. Above that the appearance will change (but that need not be bad - just there is trade off for brightness vs fire

 

[Lorelei]

Date: 11/21/2009 7:00:54 PM
Author: Garry H (Cut Nut)
I prefer diamonds slightly shallow - say P40.5 C34.5 because that makes any ills not a problem (with hi symmetry you can go to a steeper deeper - often up to 35/41 - with tables below 60% for under half carat and reducing as the diamond size increases to say under 58% above 1ct.

As for the variations - use this rule - if tolkowsky is perfect then use the 5:1 rule:

for every plus 1 degree crown subtract 0.2 degrees from the pavilion
for every minus 1 degree crown add 0.2 degrees to the pavilion

This works well from 32 to 37 crown. Above that the appearance will change (but that need not be bad - just there is trade off for brightness vs fire

Thanks Garry!