In most places where gold is used it's because it doesn't react with most things including air, as well as being opaque so you don't need to keep reapplying the surface. To fully answer your question we need to know the environment where it will be used. Iron rusts, sodium absorbs water from the air, so their opacity may be irrelevant to the application you have in mind. DT
________________________________ From: Ryan Simpkins <astro@ryansimpkins.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Friday, June 27, 2014 12:42 AM Subject: Re: [Utah-astronomy] Opaque vs Transparent
On Thu, June 26, 2014 21:04, BWFlowers wrote:
Well, might as well ask this also- what element is the most transparent? I'll assume it is hydrogen unless corrected, but is it fair to compare a gas to a solid? So I will amend the question to what SOLID element at room temperature (70 degree F.) is the most transparent?
For information about how transparency of solid materials is determined, this may be a good starting place: http://en.wikipedia.org/wiki/Transparency_and_translucency#Light_scattering_...
It may also lead you to an answer about non-transparent surfaces. (From the article:)
"When light falls onto a block of metal, it encounters atoms that are tightly packed in a regular lattice and a "sea of electrons" moving randomly between the atoms.[11] In metals, most of these are non-bonding electrons (or free electrons) as opposed to the bonding electrons typically found in covalently bonded or ionically bonded non-metallic (insulating) solids. In a metallic bond, any potential bonding electrons can easily be lost by the atoms in a crystalline structure. The effect of this delocalization is simply to exaggerate the effect of the "sea of electrons". As a result of these electrons, most of the incoming light in metals is reflected back, which is why we see a shiny metal surface."
That article links to more articles on the subject, and those more still. A few of them look like you'll need a fairly advanced understanding of physics and math to really understand.
I guess all of this is a long way to say, "I don't know either, but it sure is interesting." :)
-Ryan
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