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I've followed an old Blender Guru tutorial on creating muzzle flash, using it in Cycles instead of Blender Render as he did. The mesh is shaped like a rounded double-ended cone, then has Subsurf and Displace modifiers applied to it to create the flared effect. The material uses a 50/50 mix of Emission and Volume Scatter shaders plugged into the Volume output.

When rendering the scene, bright lines appear on the edges of the displaced mesh, highlighting them. I've been learning 3D modelling/rendering for the past several months so am still relatively new and unsure as to what is causing this, it's as if the light rays are trapped in the sharp edges.

This issue doesn't pertain to this particular model or scene either, as I tried modelling it from scratch again in a different scene and had the same issue. Could anyone please advise me as to how I could stop the bright edges appearing? Ideally the orange colour should just fade out.

Muzzle flash rendered, with modifiers and without modifiers

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enter image description here

Your mesh apears to be non-manifold. Specifically, it looks like you have split faces, or 'holes'. Volumetric shaders require manifold geometry to work correctly. Remove doubles, ensure that the geometry is clean, and do another test render.

Edit: Apply Scale Ctrl A > S should also be done for this object. Note that your object has a scale of 0.006 which can have consequences and cause artifacts. Try to keep a scale of 1 on your object, unless there is a specific reason not to. See Campbell's explaination on why/how non 1:1:1 scaling and rotations can cause issues within Blender (This is true for other 3D apps as well).

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  • $\begingroup$ Thank you for the quick response! I've removed doubles and checked that the mesh is otherwise good. Doing so removed the stark white segments at the front, which I'm really appreciative of, however unfortunately the edges are still lit up: tinyimg.io/i/ybbKRe8.jpg $\endgroup$ – user32212 Nov 4 '16 at 18:03
  • $\begingroup$ Oops, I missed the other obvious factor. Apply scale on the muzzle flare object (Ctrl A > S). Your Displacement modifier is going to go bonkers, so turn it down to something like 0.1 You'll likely have to adjust your displacement texture as well, since it's not using UVs. $\endgroup$ – Derek Watts Nov 4 '16 at 19:06
  • $\begingroup$ Thanks again for getting back to me, I really appreciate it. I've applied the scale and the rotation too, then reduced the strength of the Displace modifier and the size of the Clouds texture it uses. Unfortunately the issue still persists! tinyimg.io/i/P9Pj2I9.jpg Here is the .blend file containing just the muzzle flash, if you or anyone else could take a look at it I'd be very grateful: dropbox.com/s/hxih2tmr0m8mae9/MuzzleFlash.blend?dl=0 $\endgroup$ – user32212 Nov 4 '16 at 20:16
  • $\begingroup$ Yeah, the geometry is getting too extreme at those out edges. It appears that there is clipping perhaps due to floating point / precision errors. After fiddling with it, I've found that decreasing the overall strength of the displacement modifier helps the most, followed by triangulation and a bevel. Take a look at my comparison .blend $\endgroup$ – Derek Watts Nov 5 '16 at 5:54
  • $\begingroup$ You are a godsend, thank you so much! That is perfect and I learned something new too, I'm very grateful for you taking the time to stick through and fix it. Have a great day! $\endgroup$ – user32212 Nov 5 '16 at 12:04

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