Wasn't it Brent G who wrote:
>Here's my code:
>difference {
>         box {
>                 <-2, -1, 0.1>, <2, 1, 1>
>                 texture { T_Stone10
>                           color filter clock }
>         }
>         text {
>                 ttf "timrom.ttf" "Text" 0.15, 0
>                 pigment { BrightGold
>                           color filter clock }
>                 finish { reflection .25 specular 1 }
>                 translate -1.05*x
>         }
>}
>
>Which is What I want to do, but isnt' valid.  What I'm trying to do is 
>change the transparency of the objects for an animation so they fade in 
>over the course of the animation. clock goes from 0 to 1.

1. For a plain colour like BrightGold, a valid syntax is like this:

         text {
                 ttf "timrom.ttf" "Text" 0.15, 0
                 #declare CFC = color filter clock;
                 pigment { BrightGold  + CFC }
                 finish { reflection .25 specular 1 }
                 translate -1.05*x
         }

2. For a complicated texture like T_Stone10 you can't apply filter to 
   the whole thing. What you'd have to do is take a copy of the 
   T_Grnt3a, T_Grnt17a and T_Stone10 declarations from stones1.inc and 
   change all the rgbt colours into rgbft, inserting "clock," as the 
   fourth component, like this:

   #declare T_Grnt3a =
   texture {
   pigment
    {granite
     turbulence 0.6
     color_map
      {[0.000, 0.153   color rgbft <0.831, 0.631, 0.569, clock, 0.447>
                       color rgbft <0.925, 0.831, 0.714, clock, 0.678>]
       [0.153, 0.297   color rgbft <0.925, 0.831, 0.714, clock, 0.678>
                       color rgbft <0.871, 0.702, 0.659, clock, 0.475>]
       [0.297, 0.441   color rgbft <0.871, 0.702, 0.659, clock, 0.475>
                       color rgbft <0.831, 0.631, 0.569, clock, 0.918>]
       [0.441, 0.763   color rgbft <0.831, 0.631, 0.569, clock, 0.918>
                       color rgbft <0.937, 0.882, 0.820, clock, 0.655>]
       [0.763, 1.001   color rgbft <0.937, 0.882, 0.820, clock, 0.655>
                       color rgbft <0.831, 0.631, 0.569, clock, 0.447>]
      }
    }
  }

3. However, this doesn't cause the object to fade in during the course 
   of the animation. That's not what "filter" does, you are probably 
   thinking of "transmit". This is particularly noticeable in the case 
   of the Black layer of T_Stone10. When the layer is "Black + filter 0" 
   it is opaque and black. When the layer is "Black + filter 1" then 
   light is considered to pass through the object, but on the way 
   through the colour of the light is changed to being completely black.

You can easily do the plain colour with transmit, but the layers of that
stone texture already contain some transmit. So you'd have to modify
them so that the transmit varies from the initial value when clock=0 to
1 when clock=1, something like this:

#declare T_Grnt3a =
texture {
pigment
 {granite
  turbulence 0.6
  color_map
   {[0.000, 0.153   color rgbt <0.831, 0.631, 0.569, 0.447+0.553*clock>
                    color rgbt <0.925, 0.831, 0.714, 0.678+0.322*clock>]
    [0.153, 0.297   color rgbt <0.925, 0.831, 0.714, 0.678+0.322*clock>
                    color rgbt <0.871, 0.702, 0.659, 0.475+0.535*clock>]
    [0.297, 0.441   color rgbt <0.871, 0.702, 0.659, 0.475+0.535*clock>
                    color rgbt <0.831, 0.631, 0.569, 0.918+0.082*clock>]
    [0.441, 0.763   color rgbt <0.831, 0.631, 0.569, 0.918+0.082*clock>
                    color rgbt <0.937, 0.882, 0.820, 0.655+0.545*clock>]
    [0.763, 1.001   color rgbt <0.937, 0.882, 0.820, 0.655+0.545*clock>
                    color rgbt <0.831, 0.631, 0.569, 0.447+0.553*clock>]
   }
 }
 }




-- 
Mike Williams
Gentleman of Leisure

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