[Radiance-general] Determining Specularity Values - Spandrel Panels: Marble vs Fritted Glass

[R Fritz]

Nastassja,
> Marble – Originally white, but panels have become grey with dirt  
> over time, not polished, dull finish
> Type:                Plastic
> Colour:             (0.91, 0.91, 0.83)
> Specularity:       ?????? (I think this may be low because it is not  
> polished marble)
> Roughness:      0.05 (???)

Probably much darker than that, perhaps as low as 0.5.  You can  
estimate its reflectance with a camera with a telephoto lens (or a  
spot meter) and an 18% grey card; procedure at <http://www.kodak.com/global/en/consumer/products/techInfo/am105/am105kic.shtml 
 >. Use a tripod and stand far enough off so that your shadow doesn't  
affect the measurement.

I don't have any good ideas for frit glass--perhaps the manufacturer  
has some information?

Randolph
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