Re: Trying to locate black glass with n = 1.567
From: Danny Rich (DannyRich_at_softhome.net)
Date: 09/23/04
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Date: Thu, 23 Sep 2004 22:16:23 GMT
As Steve Westin pointed out there is no "black glass" with exactly this
refractive index. This number is a theoretical abstraction for the purpose
of defining a physical scale of reflectance. Actuall working standards of
specular gloss are made from glass with a refractive index closer to 1.52,
again as pointed out by Steve.
The point is that if you know that a standard of refractive index 1.567
reflects (4.8788%) at 0° then you can use Fresnel's equation to predict how
much it light will be reflected at 60° for a glass of refractive index
1.520. Then the gloss reading is just the ratio of the specular
reflectances. Standard reference materials are used to test conformance of
geometric conditions and you should not need an ongoing supply of those.
Danny Rich
"Steve Sands" <hybridyne2000@yahoo.com> wrote in message
news:4c9fff45.0409230935.64fe1ce1@posting.google.com...
> I have been trying for days, to locate a good source for black glass
> with a refractive index of 1.567 the primary standard for specular
> gloss. I will need an ongoing supply.
>
> Can anyone recommend an alternate glass or filter that would suffice?
>
> I was thinking of Schott BG1.
>
> Thank You
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