Discover the Science Behind Why Diamonds Shine - Explained!

[Acuben]

While I was looking at the backlight of the bicycle, (many times it was bright during night time with little light so I thought it was on) a question rose
Say you have a block of an ugly transparent glass and a block of nicely carved diamond sitting infront of the window.

If you took optics physics, you'd say because of index of refraction, total internal reflection, just because it is ;) ,etc

But even with light bending, splitting, internal reflection, the light that diamond shines to your eyes should be the same as the ugly block of glass. (but in reality it's not).
Even if the diamond "traps" the light, the total number of light rays going in and out should be the same as the ugly block of glass.

so why is it that the diamond (or even fake jewelery) look shiny?

or could it be that the number of light rays from diamond is same as the ugly block, but it just "seems" shinier?

 

[flintsmith]

The junky glass sends the light out in all directions equally. A faceted diamond sends the light out in only a few directions. As you turn it, you see a few sparkles and your brain remembers those. It forgets that many times it's actually less bright than a hunk of glass. When the light is directed away, the stone seems dark.

The brightness of the two, averaged over all directions, would be the same, but your eye notices the flashes and your brain remembers those.

 

[Sniperman724]

I am guessing it is just how the piece of glass is cut, depending on the shape, the light can be "trapped" inside of the glass/diamond, which would then make it look like it is shining.

 

[Redbelly98]

Diamond looks shiny because it reflects 4 times as much light as glass.

A diamond surface will reflect about 17% of the light incident upon it, while glass reflects only about 4%. This is due to diamond's higher refractive index, 2.4, vs. 1.5 for glass.

 

[Andy Resnick]

But even with light bending, splitting, internal reflection, the light that diamond shines to your eyes should be the same as the ugly block of glass. (but in reality it's not).
Even if the diamond "traps" the light, the total number of light rays going in and out should be the same as the ugly block of glass.

so why is it that the diamond (or even fake jewelery) look shiny?

The optics of a well-cut diamond are a combination of several factors (which you note), but also include dispersion and the geometry of the faceted diamond.

(from http://www.edwardjayepstein.com/diamond/chap11.htm): Marcel Tolkowsky calculated the formula for the ideal proportions of a cut diamond. Tolkowsky's formula gave the optimum ratio between the angles of facets opposing one another in a diamond. Following this formula, a cutter would achieve the maximum refracted (or "inner") light with the least sacrifice of reflected (or outer) light. This formula led to the popularization of the so-called "brilliant cut" diamond, which had fifty-eight facets polished exactly to the tolerances of the ideal proportions.

His book is available online:

http://folds.net/diamond/index.html

 

[turbo]

The optics of a well-cut diamond are a combination of several factors (which you note), but also include dispersion and the geometry of the faceted diamond.

(from http://www.edwardjayepstein.com/diamond/chap11.htm): Marcel Tolkowsky calculated the formula for the ideal proportions of a cut diamond. Tolkowsky's formula gave the optimum ratio between the angles of facets opposing one another in a diamond. Following this formula, a cutter would achieve the maximum refracted (or "inner") light with the least sacrifice of reflected (or outer) light. This formula led to the popularization of the so-called "brilliant cut" diamond, which had fifty-eight facets polished exactly to the tolerances of the ideal proportions.

His book is available online:

http://folds.net/diamond/index.html

Thanks, Andy. The Brilliant cut has been adapted to gem-stones of lower refractive indices, too. There are some nice "emerald" cuts that take advantage of stones with higher refractive indices. My faceting machine can't cut diamond (at least not effectively), but I have had a lot of fun faceting sapphires from around the world.

 

[Andy Resnick]

My faceting machine can't cut diamond (at least not effectively), but I have had a lot of fun faceting sapphires from around the world.

That's cool! Have you ever played around with anything like iolite, tourmaline, or anything else birefringent?

http://www.nordskip.com/iolite.html
http://www.gemstonebuzz.com/tourmaline

 

[turbo]

That's cool! Have you ever played around with anything like iolite, tourmaline, or anything else birefringent?

http://www.nordskip.com/iolite.html
http://www.gemstonebuzz.com/tourmaline

I have cut LOTS of tourmaline, since that is the Maine state gem (sells well, here) and can be found in a number of locations that are/were open to the public. There was a high-end jewelry store in the state capitol, and when I would show up with a selection of faced stones, the owner never let me leave with any tourmaline. He wanted it all, even though I kept raising the price. He could pass on spinel, sapphire, Tsavorite, etc, but he simply had to buy all my tourmaline.

I have some untreated Tanzanite rough that I'll facet someday. It is trichroic, and ought to have some interesting colors based on the light-path through the cut stones.

 

[Andy Resnick]

I have some untreated Tanzanite rough that I'll facet someday. It is trichroic, and ought to have some interesting colors based on the light-path through the cut stones.

Like this:?

This website seems to indicate heating the stones removes the trichroism (?)... do you know the cause of the phenomenon? What's the crystal structure of Tanzanite?

http://www.moregems.com/pages.php?pageid=30

 

[turbo]

I don't know the physical properties that cause the color-change. My rough stones were bought from a friend who often went to Africa to buy gem rough. Depending on orientation, my Tanzanite can look purple, blue, or reddish-orange. I had bought heat-treated rough from him before, and when he offered non-treated rough at a significant discount, I bought some, figuring I'd play with cut-pattern, orientation, etc and see what comes out. If the stones end up looking crappy, I could always get a knife-making friend with a muffle furnace to treat the stones after the fact.

 

[Acuben]

Diamond looks shiny because it reflects 4 times as much light as glass.

A diamond surface will reflect about 17% of the light incident upon it, while glass reflects only about 4%. This is due to diamond's higher refractive index, 2.4, vs. 1.5 for glass.

so diamond acts more like mirror compared to glass?
very simple and straight answer xD

The junky glass sends the light out in all directions equally. A faceted diamond sends the light out in only a few directions. As you turn it, you see a few sparkles and your brain remembers those. It forgets that many times it's actually less bright than a hunk of glass. When the light is directed away, the stone seems dark.

The brightness of the two, averaged over all directions, would be the same, but your eye notices the flashes and your brain remembers those.

in another words, it's an illusion?

 

[flintsmith]

Yes. An illusion suggesting an internal light source. The incident light = the output light for both rough glass and faceted diamond. The faceting just gathers the incident light and controls the output angles to produce bright spots. Place a diamond in the sun in an otherwise darkened room and look at the spots of light spread on the ceiling. If you put your eye at one of the beams, the stone is bright. Put your eye between the spots and the stone will seem dark(er).

Refractive index doesn't affect that calculation. It changes the amount of light entering or leaving the stone by changing the angles, but the totals are unaffected. As the refractive index drops, cutters make more and more of a point on the back of the stone, trying to keep total internal reflection in the back so light only escapes out the front.

There are rare colored stones that output more visible light than they take in, dropping UV (?) light down to visible, but I have not heard of diamonds doing that. Maybe some of the exotic colored diamonds are fluorescent?

"Mogok rubies possesses a strong red fluorescence and the hue runs toward the magenta end of the color spectrum. Rubies from Mong Hsu tend to have more of a blueish hue. Although Thai rubies tend to have a purer purple-red body color, their lack of red fluorescence makes them appear dull when compared to Burmese (Mogok) rubies."

from http://www.khulsey.com/jewelry/gemstones_ruby_mogok.html

 

[donutz610]

They are made up of crystaline prisms that reflect and refract any lght that they come in contact with, making them shine.