What exactly is the difference between the specular reflection of a mirror, water...

[Shindoh]

Hey, it's me again.

I only recently started to see what Briggsy (a member of this forum, and creator of www.huevaluechroma.com) meant, when he said, that specular reflection is not just determined by the smoothness of a surface.

It's as clear as day to me now, when I think of how different smooth surfaces may have a "clean" (sharp) contoured specular reflection of environment objects in common, which indeed depends on surface smoothness, BUT how the strength of the light reflected is in fact different among them. The amount of light reflected. Although the specular reflection of objects around the surface are all reflected cleanly and clearly, the amount of light, the strength of light is less.

If for example we look at glass, compared to a mirror.
Then I looked at a picture of a sea reflecting the scenery behind it. And it looked as if the reflection was almost as strong as in a mirror in fact. I barely saw any difference between the colors of the actual scenery, and the colors of the scenery reflected on the sea's surface.

Now this confused me. I tried to find what exactly is different between water and glass. And I found that in fact glass has a loose, or more chaotic molecule structure, just like water. Just rigid in place. And that the reason glass for example is transparent, is because the photons of the visible wavelengths of light aren't strong enough (don't contain enough energy) to actually move the neutrons of glass atoms to a higher energy level.
And according to the energy band theory, there are gaps between energy levels of neutrons. Meaning that if the energy of the photons is not sufficient to increase the energy level of the neutrons, to interact with them, they will just pass through.

EDIT: "I also noticed that the specular reflection on a black piano (standing right next to me) almost appears to be mirror like, just that perhaps the mix of the black color of the piano in its' diffuse reflection with the specular reflection decieve my eyes and make the specular reflection appear weaker. As if they share the space of the surface, just one more than the other.
Now when I think about it, Briggsy said, that specular and diffuse reflection are simulataneous processes, of course we know that. But did You mean also on an atomic level? As in, the neutron of an atom absorbs the energy of a single photon (for example) and splits the energy it absorbs and the one it gives back out again? So the energy would be split between what is sent out in specular reflection and what is absorbed and sent out? I feel like I am missing something here."

So what exactly is the difference between water, a mirror (which essentially uses metal coating), and glass?

How is the strength of specular reflection found, or determined?
(not just for these, but in general)

Thanks for Your time. =)

[Conniekat8]

Are you needing to know this in order to draw or paint it, or for some other purpose?

I think most that draw and paint it, do it from observation, without worrying too much (or at all) about the underlying physics of it

[arenhaus]

So what exactly is the difference between water, a mirror (which essentially uses metal coating), and glass?

Strength of Fresnel effect.

[briggsy@ashtons]

Water, glass, your black piano, and most glossy nonmetallic objects are all much the same: they all specularly reflect just a few percent of a light ray that hits the surface perpendicularly, increasing towards 100 percent for a light ray hitting the surface at a very low angle. This is the Fresnel Effect that arenhaus mentioned. The specular reflection on the black piano only appears to be stronger than the others, because it is not swamped by any diffuse reflection or transmitted light.

Metals are different: because of the way they share electrons they specularly reflect close to 100 percent of the light hitting the surface from any angle (though less than 100 percent for some wavelengths in the coloured metals):

"Metals are defined as materials in which the uppermost energy band is only partly filled. This can be imagined to be the logical outcome of shrinking the band gap of a semiconductor to zero. The highest energy attained by electrons in the resulting single band is called the Fermi energy or the Fermi level in a one-dimensionalsituation. More correctly, this is known as the Fermi surface in the three-dimensional crystal.
The key point about a metal is that the higher empty electronic energy levels of a metal are so close to the uppermost filled levels that they form an essentially continuous band of allowed energies. Above the Fermi energy almost all the levels are empty (at absolute zero they are all empty) and so can accept electrons excited from lower energy levels. To a first approximation this means that all incident radiation can be absorbed,irrespective of its wavelength.
Intuitively, this would lead one to expect that a metal should appear black. However, each excited electron can immediately fall back to the state that it came from at once, emitting exactly the same energy, causing a flat piece of metal to appear reflective. Ordinary mirrors are metal films deposited onto glass. In a good mirror the absorption and reflection should be identical over thewhole of the spectrum and all colours accurately reflected. Exactly the same absorption and emission processes lead to finely powdered metals having a black appearance. This is because the re-emitted (i.e. ‘reflected’) photons are reabsorbed again in nearby grains and ultimately do not emerge at the ‘angle of reflection’ and so do not enter the eye".

Tilley, 2011 - Colour and The Optical Properties of Materials (2nd edn), p. 477.

[Shindoh]

Briggsy: Thank You, Your answer is always spot on, exactly what I was looking for. And that book You mentioned definitely looks interesting, I should give it a read.

Arenhaus: Thank You for mentioning that, I haven't heard of that before.

Conniekat8: In order to draw something, especially from imagination, I need to understand it, to know how it works. So I will then be able set up own situations or estimate outcomes. And if You want to simplify something, consider this: You can only simplify something that You know more of. If I am just painting what I see, then I am just painting what I see. I am just copying without understanding. This doesn't give me as much freedom and control. I might know how to draw some things and effects, but in the end all I can do is draw the things I drew before, and combine them in different ways for something new. But why not learn the rules of the world we live in? Learn the rules, so You can bend the rules for Your paintings. Think what would happen if You learned math just by memorizing the the outcome of an equation, but not how to get there. As in, 4 + 5 = 9, but what is 5 + 5? You can only solve new equations, because You know to use +, You know how it works.

You can feel the beauty of understanding and applying Your knowledge in art, when You learn about perspective and anatomy with all it's proportions and ratios for the first time. You will feel like a whole new world has opened in front of You, many new possibilites of visual expression. And armed with new knowledge, You can be more and more inventive, while still making something believable. In the end You have more control over what You are doing. You don't just get a beautiful effect by accident, but because You intended to do so. You know why You apply a certain color at a certain area, what effect it will have, what it will look like.

You don't have to do it. But it makes me feel limited, if I come to a point where I want to draw or paint something, and suddenly I don't know how to achieve the visual image I have in my mind. I am generally curious about the things around me, it makes me feel better understanding them. It makes my world more colorful and changes the way I see things. It allows me to see more of the world. I might look at the sky and see it is blue. Then I wonder, why is the sky actually blue? After finding the answer, not only do I see a blue sky, but I know what is happening there every time I look at the sky. Or I see a specular reflection on the floor, maybe it's in the night, and I see the lights of cars creating interesting beams of light on the street. I could just accept it and say I see those beautiful lights, or I wonder how they work. Why for example, they seem to follow me around on the floor, as I move around the car? Why is the beam not all over the street in front of the car, where the light theoretically hits? And why for that matter is the beam not endless, but seems to fade and basically look like a light pillar, decieving my eyes seemingly going into the floor. Things like this enrichen my life.

EDIT: Consider this, even when You are painting and drawing from observation, the more You understand how the things around You work, the easier it will be to paint what You see. You might be sitting in a bus, drawing a person You see. Your existing knowledge will recognize some information that is relevant to getting the drawing nailed. You see the main angle of the person's body in relation to Yours, the angle and tilt of the head compared to body, the angles the arms are in compared to the body. You know the general mass and volume of the body parts and their ratio to each other, which You alter according to the person You see.
You recognize the general flow of the wrinkles in the clothes, aided by the knowledge why they are that way. You see where the light is coming from, where the main light source is located. Combined with Your knowledge about how light works and what influences the values of the shadows (for example why one area in a shadow at a similar angle has a more bright value than another), the correct behaviour of light combined with Your knowledge about the volumes of the body parts help You to finish off Your drawing or painting. Basically by recognizing all this information, You might just have to take a few looks at the person, and then be able to finish Your drawing or painting on Your own, because You memorized all the necessary information of the situation and can fill in the rest with Your knowledge of the relevant subjects, processes going on.

In order to recreate something, we first need to know how it was created in the first place.

In the end it's about visualizing something, that You have on Your mind. Something that You can't yet see, but want to make visible. Something, that perhaps You want others to see. To show them Your vision.

[Conniekat8]

Yea, that's why I asked you why you want to know... sometimes it's useful, sometimes people go way overboard with in depth theory, and over complicate things.

Being an engineer ion my first career, I'm quite prone and capable of over complicating things and analyzing them ad-infinitum. Some of what you were saying made wonder if you were not heading in that direction.

Learning things in depth can be very helpful and very interesting at the right time and place, as long as it doesn't come at he heavy expense of actually putting it in practice, if being a working artist is your goal. Just something to be aware of, so you can try and check yourself if you go too far into one direction

In order to recreate something, we first need to know how it was created in the first place.

Perhaps. Learning details of light behavior in engineering school hasn't made me pick up working with color for the first time any faster then students who are barely past basic algebra.

Similar with swimming which I do as somewhat competitive recreation, learning gobs of information about fluid mechanics and dynamics has only made a very limited impact on my swimming.

On both counts it has put me in a position where I know so much more theory then I can put into practice that it can be maddening at times.
Just be sure to find a good balance between theory and practice.

[briggsy@ashtons]

You're very welcome Shindoh. The real problem with the simplistic approach to colour (the "classic" colour wheel and so on) is that it makes students imagine that they "know" colour theory. So when that theory turns out not to tell them what they need need to know, they assume that all they need is practise, when really they could also use some better theory.

[truro]

I love reading about this kind of stuff and applying it to my work - thanks Shindoh and Briggsy. Can anyone recommend an excellent book about lighting and materials that's written on more of an artist's level - in particular one that's never taken physics and never got past Calc 2?

[dpaint]

James Gurney Color and Light

[dose]

Perhaps. Learning details of light behavior in engineering school hasn't made me pick up working with color for the first time any faster then students who are barely past basic algebra.

What you are probably missing is details about paint behavior, which is it's own little world that you probably would not have touched on as an engineer. In fact, a lot of painters don't really understand this either, which is a cause of much frustration.

Agree with your point about balance. There is definitely a trap of acquiring knowledge in a vacuum and never moving on to execution. A mistake would be to recommend avoiding knowledge in reaction to this problem. You don't seem to be recommending this, but I have seen others who do.

Personally, I am a big proponent of "awareness", which is subtly different than "knowledge".

[briggsy@ashtons]

I love reading about this kind of stuff and applying it to my work - thanks Shindoh and Briggsy. Can anyone recommend an excellent book about lighting and materials that's written on more of an artist's level - in particular one that's never taken physics and never got past Calc 2?

This might be what you are after:

http://www.webexhibits.org/causesofcolor/

[Conniekat8]

What you are probably missing is details about paint behavior, which is it's own little world that you probably would not have touched on as an engineer. In fact, a lot of painters don't really understand this either, which is a cause of much frustration.

You absolutely hit the nail on the head there!!! I don't know about a lot of painters, but for my beginning painting level, that's a painfully obvious issue at the moment. But... i just started climbing up the learning curve, so that shall pass eventually.

Agree with your point about balance. There is definitely a trap of acquiring knowledge in a vacuum and never moving on to execution. A mistake would be to recommend avoiding knowledge in reaction to this problem. You don't seem to be recommending this, but I have seen others who do.

Agreed

Personally, I am a big proponent of "awareness", which is subtly different than "knowledge".

It is interesting that you bring this up... my current painting teacher has a saying that's almost a mantra: "What is the FIRST thing I want you guys to do when you come to class?" "BE AWARE"

[Jason Ross]

I started using V-ray for sketchup and just about ALL of my questions were answered. If you have the access, you should experiment with some 3d rendering application. It will help.