Entre otras cosas, Qleemish tuvo a bien escribir:

> thx jellby, btw, nice sig. ure right, they are solid... unless u turn on
> filter, in which case only the part affected by the difference is solid
> (see below). still a problem, but it does let us overlay text etc then. so
> now only one question left, how do u change the thickness of the walls, so
> that u could, for example, cut a hole in one side of a cup and have it
> appear [thickness] at the top (and therefore from <0,10,0>. any ideas
> other than john's? (his still doesnt get rid of the 'solidness' (notice
> quotes warp) ie, we couldnt do cutaways very well. i still think it would
> be great if 3.6 had a thickness modifier built in.

Objects in povray have no thickness, you have to "create" it by subtracting 
a smaller copy of the object from the original one, like this:

------------
#include "colors.inc"

camera { angle 10 location <1, 4, -30> look_at <0, 1, 0> }

light_source { <20, 20, -40> color White }

difference{
  lathe {
    cubic_spline
    8,
    <0,-.5>, <0,-.5>, <1,-.5>, <.4,-.25>, <.2,0>, <1,1>, <1,2>, <.7,2.3>
    pigment {Blue}
  }
  lathe {
    cubic_spline
    8,
    <0,-.5>, <0,-.5>, <.9,-.5>, <.3,-.25>, <.1,0>, <.9,1>, <.9,2>, <.6,2.3>
    pigment {Yellow}
  }
  box{ <0,0,0>, <4,1,-4> pigment {Green} }
}

plane { <0,1,0>, -.5 pigment {Red} }
------------

This is not specific to lathe objects, this happens to any object, they're 
just an infinitely thin surface that divides the world in an "inside" and 
an "outside", no thickness.

-- 
light_source{9+9*x,1}camera{orthographic look_at(1-y)/4angle 30location
9/4-z*4}light_source{-9*z,1}union{box{.9-z.1+x clipped_by{plane{2+y-4*x
0}}}box{z-y-.1.1+z}box{-.1.1+x}box{.1z-.1}pigment{rgb<.8.2,1>}}//Jellby

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