> clipka <ano### [at] anonymousorg> wrote:
>> Am 09.07.2017 um 18:24 schrieb Norbert Kern:
>>
>>> Fresnel lets the iridescence disappear
>>
>> What?
>> It shouldn't do that.
> 
> 
> 
> Then - try this replacement of the terminal part of code in message 1.
> You will recieve pure dark grey (rgb 0.05).
> 
> Norbert
> 
> 
> 
> 
> #declare RotBox =
> object {
>   RoundBox () scale 1.2
>   rotate <45,0,35>
> }
> 
> merge {
>   object {RotBox scale 0.9}
>   object {RotBox translate <1,0,0>}
>   object {RotBox translate <-1,0,0>}
>   object {RotBox translate <0,1,0>}
>   object {RotBox translate <0,-1,0>}
>   object {RotBox translate <0,0,2.5>}
>   object {RotBox translate <0,0,-2.5>}
>   hollow
>   pigment {color rgb 0.001}
>   finish {
>    reflection {1 fresnel on}
>    irid {0.05 thickness 0.315}
>   }
>   rotate 90*x
> }
> 
> 
> 

If there is no ior, or an ior of 1, fresnel reflection result in NO 
reflection at all. Fresnel reflection depend on a change of ior at the 
surface.
So, in this example, you NEED the iors.

No fresnel and no thansparency = ior have no effect.
Fresnel reflection ABSOLUTELY NEED an ior <> 1, normally larger than 1.
And, obviously, ior is essential if you want any refraction.

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