Here's the source for an isolated area of clouds, which I used for that scene...
difference {
sphere {
0, 1
scale <1500,110,1000>
translate <0,250,2750>
}
plane {
y, 250
}
pigment {rgbf 1}
hollow
interior {
media {
scattering {2,.02 }//extinction .6}
/*intervals 30 // uncomment for very good qu****y
samples 1,4
confidence .95
variance 1/255*/
/*intervals 20 // uncomment for good qu****y
samples 1,2 confidence .9 variance 1/255*/
density {
spherical
scale <1450,100,950>
translate <0,250,2750>
}
density {
granite
color_map {
[0 rgb 0]
[.52 rgb 0]
[.54 rgb .2]
[.56 rgb .6]
[.58 rgb .9]
[1 rgb 1]
}
scale 3
warp {turbulence .2 octaves 3 lambda 3}
scale 2.33
scale <250,250,250>
translate 400*x // not necessary
}
}
}
}