From: rlombardo3@gmail.com   
      
   Perhaps I am misunderstanding your writing, but you begin by stating the   
   difference between specular and diffuse reflection -- this already precludes   
   absorption.  Reflecting materials whether specular or diffuse do just   
   that -- reflect.  Absorbing materials absorb the energy and re-radiate/emit.   
   They do not reflect -- either diffusely or specularly.   
      
   With 30 years of experience in infrared, I believe the definitions of   
   reflection and absorption are pretty clear to me.   
      
      
   "Salmon Egg"  wrote in message   
   news:SalmonEgg-64CA7E.22583129122011@news60.forteinc.com...   
   > In article ,   
   > "rll_sb"  wrote:   
   >   
   >> I think the poster meant to say that strongly absorbing materials are   
   >> also   
   >> strong emitters, not reflectors.  By definition, strong absorbers can't   
   >> be   
   >> strong reflectors.   
   >>   
   >>  - Russ in SB   
   >>   
   >>   
   >> "Salmon Egg"  wrote in message   
   >> news:SalmonEgg-203907.09213626122011@news60.forteinc.com...   
   >     
   >> > It is very difficult to get a flat black paint. In WWII airplanes with   
   >> > flat black paint were found to be much more visible in searchlight   
   >> > beams   
   >> > compared to planes painted with glossy paint. You first need a   
   >> > specification that including the allowable thickness of the paint.   
   >> >   
   >> > The fundamental problem is that strongly absorbing materials are also   
   >> > strongly reflecting. To get non-reflection, you need a thick weakly   
   >> > absorbing material of low refractive index. Something like an absorbing   
   >> > aerogel of low absorptivity that is thick enough would work optically.   
   >   
   > I stand by my original wording. The misunderstanding , if any, arises   
   > from the distinction between specular and diffuse reflection.   
   >   
   > If you observe letter press printing of some black inks on glossy paper   
   > specularly, the black printing can appear much brighter than the paper.   
   > Under some conditions, the developed colloidal silver negative image in   
   > gelatin emulsion, you can see positive images. Green and red inks often   
   > appears in complementary color, red and green respectively, when   
   > observed specularly.   
   >   
   > The fundamental physics is the optical mismatch at a boundary. You get   
   > big reflectivity whether the mismatch arises from lossless transparent   
   > media with a bi jump in refractive index or from lossy media with a   
   > large imaginary component in the refractive index. Metals, for example,   
   > will have strong reflectivity.   
   >   
   > Semiconductors are interesting. They have large refractive index that   
   > give fairly high dielectric reflectivity. But they are not extremely   
   > absorbing. Silicon, for example will let even red visible light   
   > penetrate many wavelengths before producing electron-hole pairs. That is   
   > why silicon was considered to be a metal at one time, but just not quite   
   > have a metallic luster.   
   >   
   > --   
   >   
   > Sam   
   >   
   > Conservatives are against Darwinism but for natural selection.   
   > Liberals are for Darwinism but totally against any selection.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)