Strange liquid appearance inside glass I am trying to make a simple scene where there is a glass bottle with some liquid inside of it. To make the liquid, I just sliced a sphere in half, gave it a volume and glass shader, and put it inside the bottle.

When I rendered it (Blender Cycles 2.83 Beta), I noticed some very strange things appearing in the liquid. (Look below)

Here is the .blend- before discovering this issue, I wanted to replace the liquid with fluid simulation. The objects that you won't need to investigate should be hidden from view.





Here is a closer view with the problems labeled:



As you can see, the borders of the liquid inside the glass have a strange "pixelated" look that does not match the resolution of the image, nor does it look realistic.

For lighting, I am using a completely black environment. I added a red and blue light next to each other to use as the main lighting.

I can also guarantee that there are no intersecting surfaces. I have no idea why this is happening. I also couldn't find any other people who have experienced a similar issue.
How it looks depends on what liquid that is. The 'pixelation' is because of the mesh of the glass shaded flat. You need smooth shading for it. However there are many more problems here. There is only one interface for light traveling from glass to liquid here so there should be only one surface, not two with a gap between them and you need to take IOR into consideration which is different when light goes from glass to liquid than the 'regular' IOR that everyone is used to that is usually between the material and air. You will have to look into physics to make it look right. See: Liquid / glass interface IOR and normals in Cycles