Yar, what be this in me rum?
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Nice work in general, but something feels very wrong about the edge of the glass and the edge where the liquid touches glass and about how the liquid surface moves… Some refraction jumps at the edge at some point at the part that should not be visible at all. Did you use real reference? Are the IOR values and amount of surfaces correct? There should be air-glass, glass-liquid, liquid-air interfaces with correct IOR values, for example glass-water interface should have IOR of around 0.86 - 0.89 depending on the type of glass and there should be only one surface where light goes from glass to water…
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Hello! Thanks for the reply.
For this, I attempted to create something of a fisheye look with the glass bottle but couldn’t get it to look right, so I ended up going with something less realistic and more cartoony. I’m afraid I didn’t use reference for this and eyeballed the look. I used two materials for the water and bottle respectively.
Do you have any resources on using the proper IOR values and creating a realistic bottle look?
I am in a bit of a weird situation right now - there is no electricity in my home due to some construction works 
so I cannot use my PC at the moment. its a disaster. But it should be back on in a couple of hours hopefully and I’ll try to answer in more detail.
Most people make liquid in a glass wrong.
Surface in surface modelling represents a light interface and if it is transmissive, then that is the interface between 2 materials. So in case of a glass container and a liquid there is only one interface between the glass and the liquid and there should be only one surface there. The interface is then where the light goes from glass to liquid and it must have the correct IOR. IOR values are given between air and a material and air is considered to have IOR of aprximately 1(vacuum to air in that case) The top part of the liquid is likely air to liquid. So the glass should have IOR of around 1.42-1.9. The bottle is likely to be made of lower quality glass and has an IOR of around 1.45 or something like that, that’s fine for the outside material of the glass. The inside surface between glass and liquid is likely to have normal pointed towards inside of the container, so the interface is actually liquid to glass. It’s easy to remember that IOR values are provided for materials that are denser then air and it’s pretty much always greater than one so when light goes from less dense material to more dense material the IOR is grater than 1. So it goes from liquid to glass. Liquid if it’s alkochol has IOR of around 1.35 so liquid to glass should be 1.45/1.35=~1.074 that’s great, because it should be greater than one. If the normals were pointing the other way it would be glass to liquid so denser to less dense material and it would be 1.35/1.45=~0.931. The top part is air to liquid so it should just have an IOR of the liquid - 1.35 if the normals are pointed towards air.
See this correct answer below 2 incorrect ones:
Why does this matter?
It does, because of the way the edge looks. Even if I have very thick glass, the edge looks as if the liquid is touching it completely and there is no gap:
If you study reference photos you will quickly see one other very common mistake - most glass we encounter in our daily lives doesn’t look like what you get when rendering with IOR of 1.5 that you get when you google “Glass IOR”. That’s because it isn’t. It’s usually much lower. You usually cannot match reference with 1.5. Because there are all kinds of glass and the most common types have lower IOR. That’s also one thing most people do wrong.
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Thanks for the write-up and links! I’ll have to dive back into this later and experiment with more drinks.
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I featured you on BlenderNation, have a great weekend!