Crumpled Aluminum Foil look in a diamond?

[haflc]

I've seen a few diamonds that look like crumpled aluminum foil, especially in outdoor lighting or very diffuse indoor lighting.
There seems to be a lack of contrast and sparkle.
This is more prominent when viewed from a slight angle.

1. Is there a reason for that, is it light dependent or based on a poorly cut stone?
2. Will all stones exhibit this to a certain extent, and will certain cuts eliminate this?

Thanks again.

 

[WinkHPD]

I've seen a few diamonds that look like crumpled aluminum foil, especially in outdoor lighting or very diffuse indoor lighting.
There seems to be a lack of contrast and sparkle.
This is more prominent when viewed from a slight angle.

1. Is there a reason for that, is it light dependent or based on a poorly cut stone?
2. Will all stones exhibit this to a certain extent, and will certain cuts eliminate this?

Thanks again.

I am not sure what you are referring to, but it sounds a lot like a phenomenon that is also referred to as crushed ice. It is the result of cutting that is creating thousands of very small virtual facets and very few or even no large to very large scintillation events.

Here is a video, http://www.screencast.com/t/TX0rrf4tqG8, I think it is posted somewhere here, but I no longer have the link, so I will take you directly to the video. It will explain much of what you are looking for. (Yssie, this also addresses your comment of the other day, as it will allow you to see the diamond in wire frame as the look changes in one degree increments.)

Around minute ten you will see a diamond tilting from 0 to 45 degrees over and over. Approx 6.5mm

Around minute thirteen you will see a visual explanation of small, medium, and large scintillation events.

Around minute sixteen you can see what happens when you use a smaller diamond of approx 4mm. Immediately after an 8mm. This has HUGE implications as to why many ladies LOVE bigger diamonds.

The video is 27 minutes long, and I give you those "mileposts" so that you can skip ahead if you wish. There are other videos there too feel free to explore, there are three or four of Peter's presentations in there.

Wink

 

[yssie]

Wink - thank you for posting that video!! I'd never seen it - it gives a fantastic overview of so many topics discussed in RT recently. I loved the small/med/lg potential sparkle event videos for different stone sizes at 13:30 and the tilt wireframes at 9:00 - avg VF size in an RB gets smaller as you tilt


A few comments and questions.

Defining "a sparkle" as in the video as the moment a direct light source is incident on a VF, the intro to the lecture lists five objectives: determining how many sparkles in a stone, how big or small, at what point does small sparkle become inconsequential, what size and frequency of sparkle do people like, how does VF shape affect sparkle. Video did a nice job of discussing the first four, I didn't see the fifth topic addressed.

Beyond size (area) and location, I would love to see a discussion on how VF shape can determine A) whether a sparkle occurs, B) whether the sparkle appears white or coloured.. I can imagine that a very long, thin VF has the potential to be normal to a wider range of direct light sources, meaning that it has a larger chance of sparkling, so does that fact change how the sparkle appears and if so, how?


Another interesting point brought up:
"Whether you see a white or coloured sparkle depends on amount of refraction, visual acuity, age, pupil diametre, lighting & specific type of lighting".
All sparkles that aren't glare are the result of a light ray refracting into the stone material and dispersing into colour, which is reflected internally and refracted out through the crown facets, so when following the path of light from any one direct light source nowhere within the stone is there reflection of 'white'. In a real stone many VFs are going to be picking up direct light at the same time, and those dispersions may intersect internally and when refracted out... but, essentially the same thing is happening within the stone in all lighting environments - refraction, dispersion, reflection, refraction - the colour we see depends on us, our angle, age, pupil diametre, visual acuity


... so haflc, I reckon a threestone with a 3ct solasfera centre and 0.5c RB sides would be perfectly matched

 

[WinkHPD]

Wink - thank you for posting that video!! I'd never seen it - it gives a fantastic overview of so many topics discussed in RT recently. I loved the small/med/lg potential sparkle event videos for different stone sizes at 13:30 and the tilt wireframes at 9:00 - avg VF size in an RB gets smaller as you tilt


A few comments and questions.

Defining "a sparkle" as in the video as the moment a direct light source is incident on a VF, the intro to the lecture lists five objectives: determining how many sparkles in a stone, how big or small, at what point does small sparkle become inconsequential, what size and frequency of sparkle do people like, how does VF shape affect sparkle. Video did a nice job of discussing the first four, I didn't see the fifth topic addressed.

Beyond size (area) and location, I would love to see a discussion on how VF shape can determine A) whether a sparkle occurs, B) whether the sparkle appears white or coloured.. I can imagine that a very long, thin VF has the potential to be normal to a wider range of direct light sources, meaning that it has a larger chance of sparkling, so does that fact change how the sparkle appears and if so, how?


Another interesting point brought up:
"Whether you see a white or coloured sparkle depends on amount of refraction, visual acuity, age, pupil diametre, lighting & specific type of lighting".
All sparkles that aren't glare are the result of a light ray refracting into the stone material and dispersing into colour, which is reflected internally and refracted out through the crown facets, so when following the path of light from any one direct light source nowhere within the stone is there reflection of 'white'. In a real stone many VFs are going to be picking up direct light at the same time, and those dispersions may intersect internally and when refracted out... but, essentially the same thing is happening within the stone in all lighting environments - refraction, dispersion, reflection, refraction - the colour we see depends on us, our angle, age, pupil diametre, visual acuity


... so haflc, I reckon a threestone with a 3ct solasfera centre and 0.5c RB sides would be perfectly matched

You are very welcome.

I believe there is another video in there on that question that discusses personal tastes. Peter (and AGSL) is very careful not to even attempt to decide what people should like. I did not look specifically at that video today, but I believe you will find some answers in that video.

Wink

P.S. I apologize for the problems resulting from hand holding the video camera, there were a few times when I was too busy watching Peter to hold the camera still...

 

[haflc]

Thanks that helps a little.

I do understand that in more diffuse lighting, light is coming into the diamond from every angle and the amount that is refracted and reflected back to the viewer is much more diffuse, and that smaller facets may decrease the effect of scintillation.

1. Does this account for the whiteout?

It looks like there is no depth to the stone, like a lot of white and some folds, as though there is a metal backing under the stone and the light is reflecting off of it, like crumpled up aluminum foil.

I've noticed it on occasion when glancing at someones ring. I didn't want to stare or ask to see the ring because it may become awkward.
And I have not had a chance to sample many diamonds outside a store to view it under outside lighting.

Hope I've described it well enough.

2. Does having a fully covered setting vs. an open setting effect this in anyway?


Thanks for your help.

 

[yssie]

Thanks that helps a little.

I do understand that in more diffuse lighting, light is coming into the diamond from every angle and the amount that is refracted and reflected back to the viewer is much more diffuse, and that smaller facets may decrease the effect of scintillation.

1. Does this account for the whiteout?

It looks like there is no depth to the stone, like a lot of white and some folds, as though there is a metal backing under the stone and the light is reflecting off of it, like crumpled up aluminum foil.

I think I can address part of this - in more diffuse lighting the light is coming into the diamond from all angles (there are hundreds and hundreds of 'direct light sources'). Each of the rays from each of those sources individually disperses just as if there was only that one light source, but because there are so many dispersed rays outputted through the crown at any given moment in time, what your pupils see from any one angle is the agglommeration of wavelengths of many dispersions - some R, some O, some Y, some G... which all put together at your eyes make "white", which contrasts with black obstruction patterns

I've noticed it on occasion when glancing at someones ring. I didn't want to stare or ask to see the ring because it may become awkward.
And I have not had a chance to sample many diamonds outside a store to view it under outside lighting.

Hope I've described it well enough.

2. Does having a fully covered setting vs. an open setting effect this in anyway?


Thanks for your help.

 

[Dreamer_D]

Most people wear poorly cut and dirty diamonds, so I would not try to learn too much about optics by looking at stones you see out and about.

 

[Karl_K]

Beyond size (area) and location, I would love to see a discussion on how VF shape can determine A) whether a sparkle occurs, B) whether the sparkle appears white or coloured.. I can imagine that a very long, thin VF has the potential to be normal to a wider range of direct light sources, meaning that it has a larger chance of sparkling, so does that fact change how the sparkle appears and if so, how?

VF shape certainly makes a difference, but it is my secret sauce so other researchers are on their own with it.
Be careful when interpreting the data in the vid.
They are using a uniform lighting environment aka dome which is not found in the real world.
It fails to answer the 3 people test.

 

[yssie]

Haha okay, keep the special sauce secret


Wink - he was very adamant that he wasn't recommending one look over another in the vid

 

[Andelain]

Most people wear poorly cut and dirty diamonds, so I would not try to learn too much about optics by looking at stones you see out and about.

Well Dreamer, we can learn what NOT to look for in a diamond by looking at stones we see on the street.