Step by Step render realistic liquid

01 MODEL the GLASS

Here we have a basic two-part model of a glass and a liquid inside. We have to break it down into three shells in order to assign correct materials. My shaky-hand outlines point out the areas we need to create: a glass, water touching the glass, and water-air surface. It is important that even though we will end up with three separate tools, there must be no gap between them.

02 SEPARATE parts

For this process, I used Live Boolean to make sure my water part fits perfectly in the glass. Notice that the inside of the glass does not have any faces where the water will be. Double surface is not cost-effective and would not render well. I used poly groups created with boolean to delete unwanted surfaces. The same process can be used to separate the water-air surface.

03 index Of refraction

Import the model in Keyshot, and drop the Solid Glass material onto the glass model. Assign the Liquid Water material to the water/glass part, and up transparency to 5. Open the Advanced section and set the Refractive Index Outside to 1.5. Apply the same material to the water-air surface, but leave the RI Outside at 1.

04 lighting Settings

This quick render has an HDRI environment set for reflections only. In the Lighting tab, set the Shadow Quality to 3 and turn Self Shadows on. Up the Ray Bounces to somewhere between 10-20, turn on Ground Illumination and activate Caustics (optional). Play with the settings to see what works in your scene.