Why does combining a surface and volume node result in a black material? 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.



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.



What is this and how can I fix it?
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.