Opacity In Gold Coated Welding Lenses it seems that reflectivity is what is important; Colored lenses absorb incoming light but do not absorb all frequencies equally, and can distort colors. Gold lenses reflect rather than absorb light. They restrict light from passing through the lens and give you a truer color palette. Both types will prevent damaging levels of UV light from reaching your eyes, so usage generally amounts to a matter a personal preference. (1) Opacity or mass absorption coefficient, if I understand the math, appears to be a function of frequency of the light and the molecular density of the material as to how far the light travels through the material. (2) If that is the case there are 6 other elements that a have a higher STP (Standard Temperature and Pressure) density and Liquid Density than gold and Tungsten having a higher Liquid density but a slightly lower STP Density. Atomic Number Symbol Name STP Density kg/m³ Liquid Density kg/m³ 75 Re Rhenium 21020 18900 76 Os Osmium 22610 20000 77 Ir Iridium 22650 19000 78 Pt Platinum 21090 19770 93 Np Neptunium 20450 94 Pu Plutonium 19816 79 Au Gold 19300 17310 74 W Tungsten 19250 17600 STP - Standard Temperature and Pressure (3) I suspect that gold is used most often, for ease of use, chemical properties, reactivity, non-radioactivity, available and cost of the material. As for transparency, Hydrogen at 0.0899 kg/m³ is the least dense element with Helium (0.1785) and Neon (0.9) next in density. (3) There is a lot of material and studies out there about using gold in various applications that sound exciting. Including Gold nanoparticles: interesting optical properties and recent applications in cancer diagnostics and therapy. (4) Thank you for asking this question it made me do research and use my brain. I invite anyone to please feel free to correct errors in my math and research. Hope this helps answer some of your questions, Jamie Bradley References 1 - GOLD-COATED THE GOLD STANDARD OF WELDING LENSES - Written on October 7, 2013 by Ryan Phillips (http://blog.phillips-safety.com/gold-coated-the-gold-standard-of-welding-le nses) 2 - Opacity (optics) (http://en.wikipedia.org/wiki/Opacity_(optics)) 3 - Dynamic Periodic Table. Dayah, Michael. (http://www.ptable.com) 4 - Gold nanoparticles: interesting optical properties and recent applications in cancer diagnostics and therapy. - Xiaohua Huang, Prashant K Jain, Ivan H El-Sayed, Mostafa A El-Sayed - Georgia Institute of Technology, Laser Dynamics Laboratory, School of Chemistry and Biochemistry, Atlanta, GA 30332, USA. (http://www.researchgate.net/publication/5870560_Gold_nanoparticles_interest ing_optical_properties_and_recent_applications_in_cancer_diagnostics_and_the rapy) -----Original Message----- From: Utah-Astronomy [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of BWFlowers Sent: Thursday, June 26, 2014 9:05 PM To: 'Utah Astronomy' Subject: [Utah-astronomy] Opaque vs Transparent Just as a pure curiosity question, that I have not been able to google successfully, and for clarity I will word the same question a couple of different ways- What ELEMENT is the most opaque? Meaning- How thin can the most opaque element be before it will allow light to penetrate it at any level? When I was in grade school, early 1960's our science teacher said that it was GOLD and I have wondered about it all these years. Personally I'd be willing to bet that gold is NOT CORRECT, or is it? The reason I think gold is not correct is that gold is used in a lot of higher end welding lenses to darken the lens against the electrical arc and is offered in various "tints" to suit the individual. On the other hand, he may in fact have been correct and that is exactly why gold is used. Thin can defined in terms of layers of molecules (100 molecules thick, etc) or an actual thickness like 1/10th of a hair thick or .00003" Expressing it in some (off-the-wall) scientific term wouldn't do a lot of good if I have no frame of reference (yeah, I'm not the smartest brick in the wall). Also I assume that the power of the light source would enter into it, so to keep the playing field level on that, let's say direct sunlight as the source. Hmmm... brings up another question- How many candlepower is the sun? To narrow the parameters a bit more, the brightness of the sunlight at sea level or here in SLC at approx 4,000 ft ASL. 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? Thanks! -Barrett <http://www.FallenStarHunters.com> www.FallenStarHunters.com <http://www.BarrettsCustomLeather.com> www.BarrettsCustomLeather.com _______________________________________________ Utah-Astronomy mailing list <http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy> http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Send messages to the list to <mailto:Utah-Astronomy@mailman.xmission.com> Utah-Astronomy@mailman.xmission.com The Utah-Astronomy mailing list is not affiliated with any astronomy club. 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