ovals and bow tie effect

[reds]

By going up in color can you minimize this effect? eg. F or G Thanks

 

[fuffi]

Hi Reds,

The bow tie effect is dictated by the pavillion depth and angles. It has nothing to do with the color of the diamond. You can find some useful info on goodold gold's site:

http://www.goodoldgold.com/shapetips.htm

 

[NewYorker]

Correct, I don't think color has anything to do with it as it appears because of the cut and light is being lost.

 

[Garry H (Cut Nut)]

It is not leakage - it is the reflection of your own head.

A deep diamond will direct light through the table right back in the same directio - like a mirror.
You can read about it at www.cutstudy.com in the artice called faceting limits by Bruce Harding (Beryl).

Punch a 1 inch hole in a piece of copy paper and look at the diamond - Whalla - no bow tie.

 

[reds]

Could not find that on goodoldgold's web site. Please advise. Reds

 

[NewYorker]

www.goodoldgold.com

 

[reds]

Looking for shape tips on goodoldgold's site-can't locate

 

[fuffi]

On the 'shape tips' page, scroll down the page to #2- 'Most fancies have bow ties'.

 

[fuffi]

I lifted this from a post from 12/2002. It reiterates what Gary said. It may be helpful:

"The bowtie is due to light being blocked from your head.  If there is no bowtie, it could mean that light is leaking out of the bottom of the diamond, and thus not reflecting back up to you, and thus the stone is dull.  Gary and Dave have both spoke many times about the bowtie effect.  They are the experts on this and may be able to help you better.  Gary said before that if you take a sheet of white paper and poke a small hole through it, and look at the diamond through the hole, the bowtie should not be there. The idea is to get the least amount of bowtie without losing the light return.  This can be difficult to achieve. "

Apparently it's almost impossible to find a marquise, oval or pear without any bow-tie. A friend of mine has an oval with no bow-tie, but her stone is obviously not well cut as it has no fire whatsoever.

 

[Garry H (Cut Nut)]

A bow tie is definitely not leaking light!

it is fully returned light - but going in the wrong direction.
If you want a 2:1 long oval you must have a bow tie.
Shorter 1:1.25 type stones should not.

 

[poopoojones]

Is the bowtie a shadow or a reflection?

 

[Garry H (Cut Nut)]

Good point!!
A reflection of a shadow - reflection of head obstructing light supply.

 

[poopoojones]

How does the 'paper with the hole' trick work? Since putting paper in front of your face does not allow light to pass through your head. Does the paper act as a reflector for the light that is normally hitting the front of your face and reflect it back from the paper into the diamond (where it can be reflected back towards the paper (and your eye in the hole)?

PS - I think the term 'reflection of a shadow' is an oxymoron since reflection requires light and a shadow requires an absence of light.

 

[Garry H (Cut Nut)]

So a negro looks in a mirror and does not exist

>>

Correct.

Because the light can not possible escape from either pavilion reflection - there is 100% light return, but there is little light to return.
Another trick is to shine a bright light on your face in a dark room - then the bow tie will be bright and the rest of the stone will be dark

You can also put a bright colored bag on your head (the gilbertson trick) and the bow tie will be a pretty colour (as will be the stars you see in a round with Ideal-scope or H&A's viewer