How do I give a completely black object a glow effect?

Question

I am trying to give an all-black object a glow effect. Is this achievable? I have seen how to create glow effects using emission and world bloom, however, this obviously has no effect on a black object.

I am using Blender 2.82 and am rendering with Eevee in case that info helps. Thank you in advance for any assistance you can provide and please note that I am day 1 into Blender.

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Here is an example of the effect I am trying to achieve:

Answer 1

It looks like you want Eevee for easy bloom?

You can repurpose an edge lining technique for it. Give your object two materials and a solidify modifier with a material offset. Make one material black, and for the other, give it emission for backfaces, but transparency for front faces:

Note that you'll need to enable some sort of blending (alpha clip is fine) and make sure you're not culling bakfaces, in material settings as shown.

There are a number of additional ways you could achieve this, constraint-placed shadowing meshes, render layers, and probably others. But this is previewable, simple enough, and should get you what you're after.

Answer 2

I know one way if you want a still image. It's kinda hard. Render your scene with the black object as a red emmision shader with bloom. Then select only the that object and delete everything else and set the emmision shaders's color to black and also set the film to transperent in render settings and render again.

Then in the composite node editor, alpha overlay the 2nd render over the first one.

If it doesn't work try flipping the order of the 1st render and the 2nd render in the alpha over node.

Answer 3

I try to achieve it in compositing.

1. Enable the Bloom Pass in View Layer Properties.
2. The color of bloom can be change with ColorRamp. Change the Alpha to 0 for the black end.
3. Subtract the original bloom.
4. Alpha Over the colored bloom.