This is something that I've been wondering about for a few days.  If one was going for realism, does everything that reflect light refract light as well and vice versa?

Well, I don't think you'd wanna put refraction on a metal. Light doesn't pass thru metal ;). I think refraction pertains most to light passing thru something and the bending that happens when it does. I ain't a scientist tho ;).

Laurie

I thought about that, and then I asked myself does mearly hitting the metal do something to refract light (at least enough to warrent attention).  In order to reflect the light has to touch the metal.  So does that touch count as a transition?

EDIT: Also I've been google searching and if you do something like aluminum refection or steel refraction, you'll get some sites giving you numbers.  That's really when my curiosity peaked on this question in general.

Laurie, what about transparent Aluminium, as used for transporting Humpback whales? Sorry, been watching too much Star Trek! Still a classic moment when Mr Scott trys to use the mouse (an early Mac?) as an oral interface.

Seriously, here's a list for common materials put together by Robin Wood

http://www.robinwood.com/Catalog/Technical/Gen3DTuts/Gen3DPages/RefractionIndexList.html

The phenomenon of refraction occurs even in metals. However, the metal is a metal because it has free electrons that can move easily. A passing electromagnetic wave (light) will cause these electrons to move. Movement of electrons (a current) creates electromagnetic waves that just so happen to exactly oppose the light that caused the electron movement. The light is extinguished as soon as it passes a few dozen metal atoms.

wonders what a sheet that is made up of a single layer of silver or gold atoms would look like

Okay thanks bill.  So it exists but it isn't something to worry about.   Now I'm left to wonder why places list the IoR of metals.

...and before you know it, you're throwing around terms like albedo, refractive indexes, and it's nothing but equations...;)

Quote - Okay thanks bill.  So it exists but it isn't something to worry about.   Now I'm left to wonder why places list the IoR of metals.

Because we use IoR in the Fresnel equation that determines how much a surface reflects. The Index of Refraction is a measure that tells us two things - the angle of refraction, and the amount of refraction. The amount of reflection is whatever doesn't refract. So knowing how much light is trying to refract also lets us know how much light is trying to reflect. Just because the refracted light gets extinguished doesn't mean we can ignore the calculation of the correct refracted amount, because that gives us the correct reflected amount, and we need that for metals as much as any other material.

Ah ok.  So if 10% of the light refracts and "goes away" it still needs to be accounted for because only 90% of the light should reflect off that surface. 

Pakled, don't forget anisotropic materials and the ones that have 3 behaviors.  ;)

When light hits an object a part of light is reflected and a part enter the object. The part that is reflect is reflected and with the part that enter the object can happen two things: Or it goes nowhere and is absorbed by the object or it pass through the object, in this case we have a transparent object. When light pass through a transparent it change its direction bending in one direction, bending in oposite direction bending nothing depending on the properties of the media, this is called refraction.

Refraction only has meaning for transparent objects. With opaque objects what happens with the light then enter the object can happen two things again: or is absorbed or it bounces several times with the atoms or molecules and goes back to outside as diffuse light.

How much light is reflected and how much light eneter the object is determined by the properties of the media ouside the object and the object itself and also depend on the angle of incidence of the incoming light.

The properties of the media are defined by three parameters: dielectric constant, magnetic permeability and conductivity. For dielectric materials (not conductors) the conductivity is zero so this parameter has no effect. For most non magnetic materials the magnetic permeability is very near to one and so we can ignore this parameter and only remains the dielectric constant and then we have a number called refraction index and so we can use Snell's law for refraction and Fresnel equation to determine how much is reflect and how much is refracted in case of transparent objects or only how much is reflected.

Part II

With metals and conductors the subject complicates. Conductors have a not zero conductivity and a perfect conductor has an infinite conductivity. An object with infinite conductivity or perfect conductor doesn't allow light to enter the object, so 100% of the light is reflected.

With metals the conductivity is very high, but not infinite, unless it is a superconductor, so light is allowed a little to enter the object and what is relected is less of 100%. The light that enters the conductor is very quickly absorbed.

The refraction index now has no sense because there is no refraction, but we can still use Frsnel equations to know how much light is reflected, but in this case the refraction index turns into a complex number because it depend on the dielectric constant and conductivity too.

I our case of making images to make thing easy we can use a fake refraction index, as metal almost reflect all incoming light we can use a big number for refraction index. The value of this number we can find empirically the one that produce the images which we want.

Until now we have ignored the magnetic permeability, that is very near one in many cases. But we with magnetic materials we cannot ignore it and so, we must forget Snell's law, refraction index and Fresnel equations and use instead the characteristic impendance of the medium and its related equations.

For transparent metals things are even more complicated. Conductors don't allow light to penetrate, but if the layer of metal is thin enough the shielding effect of the conductor decrease and some light is allowed to pass throgh. More thiner the layer more light pass and we have a transparent conductor.

The conductivity also depend on the wavelenght, the other two parameters also do. A very thin layer on our microwave window allows us to see inside the microwave owen, but this same thin metallic layer is opaque to microwave wavelenght reflecting all the microwaves and don't allowing to reach us.

Quote - wonders what a sheet that is made up of a single layer of silver or gold atoms would look like

The visor of an astronaut's helmet has a very thin gold layer.