I am impressively noobish when it comes to nodes. Maybe this is hard… Maybe it isn’t. I need a material that kind of glows from behind. I have a sword that emits dark energy. I want it to be black, but I also want it to glow… Like this square…
https://images.app.goo.gl/jzwsDiKstXTr4JBP8
Or this apple…
https://images.app.goo.gl/mG3LWkakm55xMJyc9
Probably not exactly what you’re after and I’m sure there’s a way more elegant solution, but I’m still in pre-morning-coffee mode, so here’s one take 
-
Glorious! Its not exActly what I envisioned, but I’m satisfied with the results. Question, tho. Can I make it glow more than one color?
Sure thing, just get any input really and plug it into your emissive color. You could control it with a ramp, de/recompose rbg, go crazy
Oh my.
That’s amazing.
Last question, sensei. Do you know how to make the object completely black (practically absorbing light) but have it still emit light (colored light)
fullon pitch black? you can use negative emmission values, mix it with positive ones, use light path as factor.
I guess you could do all sorts of things on top of that, add some funky musgraves or voronois to spice it up a bit.
That one didn’t work, for some reason. Is there something I am supposed to have selected in render settings? It just leaves my mesh completely black with no emission.
I don’t think so, except cranking up the samples I’m just using everything default here.
Got some crap in my nodegraph, disregard that, was just playing with stuff.
swordGlow.blend (904.8 KB)
Ah. I see. Yiure in cycles. Many thanks. You’ve been a great help
I think you mean that. It’s a post-pro. Works only with cycles. A cube has an emission material. A slightly smaller cube towards the camera with a material without emissions. If the mix is Facktor 1, the front cube is completely black. You can also simply render the sword on transparent (.png) and apply the (glow) effect in krita or your favorite “Gimp” program. Then it’s like your example.
If you’d want to do eevee it’d be a different approach I think, since there are some limitations with shaders nodes.
Maybe you can try putting lights or a small piece of emissive geo behind the object and put a shrinkwrap constraint onto them, pointing to the sword. That’d sortof keep them stuck to the back of the object. If your using area light you’d also need to put a track to constraint pointing away from the camera. You’d have limited success whit this though, but worth a try maybe.
As Mario said, doing it in post is another way to go.
Or make the sword emit particles, make a strong forcefield constrained to the camera, blowing them away from the cameras view, short life span, emissive material… 
Didn’t try this one but with a small particle size it might just work.
It will depend on if this is a static image or anim, but an easy way would be to add an emitter, something that will be the glow, and placed through the object, face to the camera…Here is a quick one in Eevee…using a Gradient texture, a Transparency and an Emissive shader, the color ramp controls how large and how strong the emissive ( as well as just scaling the emitter up or down ). Transparent controls the edge fade.
with a little work and some trial, this might work for you.
Thanks the combination of your answer am doin another’s gave me the perfect result.
