Black Bottomless Pits?

[THMG]

I'm working in GZDoom builder with UDMF format, and I'm wondering how I could go about making a black bottomless pit (e.g.the textures slowly fade to black to emphasize that the pit is particularly deadly and deep) ... a black glow doesn't seem to work, so is there any known method for making black bottomless pits?

[Kappes Buur]

Some time ago I started a map utilizing this effect, but never finished it.

 

This is easy with 3D control sectors. Depending on the depth of the pit make these sectors' ceilings/floors accordingly. Use as many 3D control sectors as you seem fit. For example this 2000 mu deep pit, where I used 26 of them:

 

Spoiler

 

The 3D control sectors are non-solid. Apply a gradient for brightness, floor/ceiling height.

 

pit_gradient.7z

Edited December 16, 2017 by Kappes Buur : added example pwad

[Quantum Dranger]

18 minutes ago, THMG said:

I'm working in GZDoom builder with UDMF format, and I'm wondering how I could go about making a black bottomless pit (e.g.the textures slowly fade to black to emphasize that the pit is particularly deadly and deep) ... a black glow doesn't seem to work, so is there any known method for making black bottomless pits?

Use 1-pixel thick sectors lining the inside of the pit and apply descending brightness to them until 0.