I'm trying to make a fluid with something dissolved into it. It's almost opaque but there are some spots of lower density solute. This is why I can't just use nodes on surface alone--I need to be able to have the opacity partly dependent on thickness.

I figured I could use a Principled Volume node and then put a low roughness, max transmission Principled BSDF node on the surface to give it the reflection and physical surface.

node setup

It didn't work. I was expecting the cube to look a bit like white watercolor paint or milk mixed with water. Instead, I got a black cube.

enter image description here

What is this and how can I fix it?

  • $\begingroup$ maybe lower your Principled Volume Density value? $\endgroup$
    – moonboots
    Commented May 28, 2019 at 6:36
  • $\begingroup$ @moonboots I need it fairly high so that it is mostly opaque-ish. $\endgroup$
    – Bobby G.
    Commented May 28, 2019 at 7:17
  • $\begingroup$ maybe show a picture of what the result should be, if you want something milky perhaps use the Subsurface value? $\endgroup$
    – moonboots
    Commented May 28, 2019 at 7:28

1 Answer 1


I had the same question, and I believe that this value under Scene Properties>Render>Light Paths>Max Bounces>Volume. When there's a surface material on the volume, it always takes at least one bounce to get into the volume. I believe this defaults to 0.

Screenshot of Blender 2.81 UI, scene render settings, with volume light path max bounces value highlighted


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