HowTo:Fix unexpected invisibility

Objects

One thing to check is whether your object is declared AND instanciated in the scene. So in the case of pre declared objects you could often find something like this :

// -- The bare necessities are here : Camera & light --
camera {
  location  <0.0, 0.5, -4.0>
  direction 1.5*z
  right     x*image_width/image_height
  look_at   <0.0, 0.0,  0.0>
}

light_source {
  <0, 0, 0>            // light's position (translated below)
  color rgb <1, 1, 1>  // light's color
  translate <-30, 30, -30>
}

// ----------------------------------------

// The object to be shown is declared here:
#declare MySphere = 
sphere {
  0, 0.5 
  pigment {color rgb <0.9,0.5,0.3>}
}
  
// ----------------------------------------
// But if one ommited the line below or commented it out :
object { MySphere } //Name could typcally followed by some transforms
//Then the object would only be declared but never instanciated

Media

Any emissive media IS totaly transparent by design. It adds to whatever is behind, wighout filtering anything out. So if your media just disappears over the background, what you can do is :

• To add some absorbing media with absorbtion<0,1,1> ...Removes the blue and green, leaving the red.

• Add some scattering media and a light_source.

• Change the pigment to rgbt<1,1,1,0.9> or rgbf<1,1,1,0.9>