why arent metals clear

In your posting on why metals are not clear it seems that you didnt get to the meat of the matter. Objects translucency depends on thier thickness and more importantly the size of the energy gap between the conductive and valence band. Metals obviously have very small gaps if not overlapping bands. Because of this even low frequency wavelengths (large wavelength) electromagnetic waves can can electron hole pairs to be generated effectively obsorbing the energy. Insulators charachteristically have large band gaps and therefore allow light electromagnetic waves of higher intensity to pass through until the threshold is met to knock an electron into the conductive band. Of course the question was posed at the visible spectrum from about 700 to 400 nanometers but insulators would become opaque at shorter wavelengths. Shifting our electromagnetic sensitivity to a much larger wavelength could give us superman vision allowing us to see through more objects kind of like x-ray vision but working on a very opposing principle

Link to the article: Why are there no clear metals?

Welcome to the SDMB, gte135q.

Isnt chrome a transparent metal? or isn’t it a metal. The silver colour is from the nickel plating underneath it.

While not disputing anything posted so far (IANAChemist), I can think of one instance where adding metal to a substance makes it “clearer”: adding lead oxide to glass in order to make it clearer and sparklier, as well as easier to cut and etch for artistic purposes. A variety of other metals (cobalt, copper, gold, uranium, etc.) may be added to glass to impart various colors – reducing light transmissibility while remaining transparent – without rendering the glass opaque per se.


You are laboring under a misapprehension.

“Chromium is a steel gray, lustrous, hard metal that takes a hard polish” (CRC Handbook of Chemistry and Physics, p. B-11) They use the chromium (“chrome”) for plating – if you plate with chromium you don’t need nickel.

As I’ve pointed out on the SDMB before, the alkali metals are transparent – in the ultraviolet. But “ultraviolet” can be a prettyy elastic term. Cesium becomes transparent below 4400Angstroms, and the visible regime is usually held to go down to 4000 A. See Born and Wolf’s Principles of Optics, section 13.3, esp. Table XXVIII.

Okay, I have another bone to pick with SDSAB Karen:

I bed to differ, but in the definitive Perseid movie of our time, Clash of the Titans, it is quite apparent that metal does reflect Medusa gaze, as Perseus uses his polished shield to turn her gaze back upon her.
Sheesh! Don’t you people pay attention?

Surely this is one of the few failings of that fine documentary film, that it did not go into the composition of the shield. Apparently, most metals are absorptive in the lithoinductive-ray portions of the electromagical spectrum, but Athena must have supplied Perseus with a shield containing a lithoinductive-ray-reflective material*. Clearly more research is needed.

*Unless you’re talking about a 1920’s-style stone-ray. Then all bets are off.

Actually, I have a bone to pick with movie. If her reflection would turn her to stone, why didn’t it turn Perseus to stone when he viewed her using the same shield? Or am I misrembering this classic of American cinema?

Well, I think that Perseus looked at her obliquely in the shield, and Medusa looked directly at her reflection - so perhaps the oblique viewing angle caused less Medusa-Rays to hit him, thereby negating or diminishing the effect…

Ahhh, and thus the threshold level of lithoinductive-rays was not reached and the stonification process was not initiated. Man, was Perseus canny or what?

Boy, you start by writing about the optics of metals and you cross over to Perseus’ shield. I have a bit of justification for writing about this one, too – I wrote a book about it.

As usual, don’t rely on movies for your info on mythology any more than you rely on them for police procedure, science, or history. Clash of the Titans may be the most accurate portrayal on film of the story (possibly excepting Jim Henson’s The Storyteller), with a screenplay by versed-in-the-classics Beverly Cross, but they still messed with the story a lot, and incorporated a huge amount of later stuff not in the oldest versions. (One big change – Athena was Perseus’ divine protector, along with Hermes. The film changes it to Zeus.)

In the oldest versions Perseus has no shield. You can see lots of examples of this in old Greek art. Perseus isn’t looking at her (in some versions of the story, Athena guides his hand), but he isn’t using the shield to try and see her. It’s only in later versions that Perseus acquires a shield and uses it as a “magic mirror” in which to view Medusa without lithification, so he can cut off her head.

I suspect that there was some feeling in the ancient world that the images in mirrors weren’t really the same as direct viewing, which sort of justified Medusa’s image not turning Perseus to stone. But I think that there’s really another reason for his using the shield as a mirror. A shield, after all, isn’t really a very good mirror, unless undented and well-polished (something I’ll bet most shields weren’t).

Greek shields were emblazoned with decorations – “devices”. One of the most common was Medusa’s head. Athena’s shield had Medusa’s head on it. According to some versions, Perseus gave the head to Athena, and she put it on her shield. But other shields had a gorgon’s head on them, too. In the *Iliad, agamemnon’s does. Curiously, in ancient Greek art, it’s Achilles’ shield that has it (and you can use its presence to identify Achilles, in fact). Ares is often shown with it on his shield, too. (Even on paintings of the Birth of Athena. But if she’s just being born, she couldn’t help Perseus cut of Medusa’s head, so that’s chronologically impossible, isn’t it? Hey, we’re Gods! We don’t need no steenking causality!)

It seems clear to me that part of the Medusa myth is intended to explain how the gorgon’s head ended up on the shield. One way is the straightforward way cited above – Perseus cuts off the head, then gives it to Athena, who puts it on her shield. But I’d like to propose another that some other teller of the story may have had in mind. Perseus gets the reflection of Medusa’s head on his shield. Then he cuts off her head, and the reflection of the head and the real head become as one, captured on the shield, and it stays there. Kinda like Wendy capturing Peter Pan’s shadow. It doesn’t make much physical sense, but it makes a sort of emotional sense.

Silver-glass mirrors, as we know them, were developed in the 15th century. A well-polished shield would be about as good a mirror as an ancient Greek could imagine (sans magic).

I hasten to point out that transparent aluminum, arenak, and inoson are all clear metals.

I think we are all forgetting that it is Medusa’s gaze and not her mere visage that petrifies victims who meet her gaze.

So therefore, if Perseus is looking at Medusa’s reflection, but Medusa is looking directly at Perseus, then he is not meeting her gaze, and therefore remains nice and warm and fleshy.

But if Medusa looks her own reflection in the eye, then she becomes a victim of her own gaze attack. Clearly, she failed her save vs. petrifaction/polymorph, too.

As for metallic/insulator transparency:

A sufficient gap between conduction and valence bands may be necessary for transparency in a given electromagnetic domain (say, the visible portion of the spectrum), but it is not sufficient. One can easily think of many insulators that are not transparent due to molecular or even macroscopic structural details that scatter or reflect incident rays. For instance: vinyl, natural rubber, wood, stone, etc.

You are also forgetting the proprietary substance from which General Products Hulls are made.

But then, it has not been established that this is a metal.

The truth is that Medusa’s reflection wasn’t off the shield, but off Harry Hamlin’s pretty-boy gleaming white teeth.