I find this a difficult subject. Materials like water and glass.
I want to create a jar filled with eyeballs. And decided to focus on glass and water material.
They are the same, but I want to tweak IOR, color, transparency etc. That’s why I added a straw, just to see ray trace physics in action.
Comments, feedback or ideas always welcome.
Happy render times
I’m only at the early stages of the course yet. I really hope I can make stuff this cool when I get further in. Nice work
You always do high quality stuff dude, even when experimenting!
Pretty neat dude. That is kind of weird looking though, the water and glass being pretty much the same lol
Had to try too !
At first tried to make something simple, a glass recipient with a sphere inside, then came the idea “Let’s make this a drink!” lol
The refraction is indeed disturbing look the stick.
glass 1,45 IOR
liquid inside 1,33 IOR
Yes, I looked up IOR on wiki refractive indices.
I thought it will help, but not much. So what is causing this glass cylinder in glass cylinder effect in my scene. Maybe too much glossy inside the jar?
Problem I have, is that my CPU / GPU is very basic. When I activate preview render mode, to tweak properties to see changes immediately. My machine gets so slow that I can not work with the interface easy.
Must have to do with the refraction and maybe it’s physically correct? I don’t know really
Maybe the glass thickness contributes?.. Try to make the gap thinner to see if changes anything
Also Make the liquid some more distinguishable color so we can see where it is sitting in all this.
Edit: Dude! Look at this!
This is just a “liquid object floating” no second layer of glass whatsoever IOR 1.33
Now… IOR 0.73 and we get close something close to what you have there!
Thank you for your thoughts. As Michael says, reference, reference … 
This is my quick and dirty reference
Strange thing is also that the water surface is showing part of the floor grid and strange reflections of the pencil. To be honest the glass wall gets thicker at the bottom. That’s why pencil is enlarged. And the foot of the glass is also thick.
I’m using and displaying only a solid glass block (with straw).
The problem is that the glass is too reflective. As can be seen on the top face.
You can not see through, while it should reflect (mirror) part of the straw and tile grid.
So, how to reduce this … maybe doing something with the backfaces …
Which backfaces?
Try only the “Is Shadow Ray” like I do in my material.
Idea: Make walls of another checker color like red, to see where the Red enters the reflection of the “surface”
Also what’s this Water node?
With water I mean of course glass material, but it acts as water.
I saw people using backface to solve this reflection problem, see Reduce reflections on inside of a glass object
I experimented with something else, just learning by doing. Left and right side are still strange (dark).
But I only tweaked the water part, not the drinking glass material (glass).
The red cube is just to see how much side reflection is coming through, on the drinking glass and content.
Looks like you’re back to the start point though…
Have you tried Principled BSDf with Transmission 1?
Also are you using 2.8? At the very least it renders faster helping your machine…
If you want, post the file so I can help you uncover the mystery
I changed the way I look at things. Instead of two glass objects. Where one acts as glass cup and the other as water. Creating a lot of glass reflection problems and node tweaks, as can be see here.
I created ONE mesh object, which act as glass and water. The difference is huge!
We have a nice, natural light index switch between glass material and the straw. nice light reflection interaction on the water (glass) top face.
I am very content with this result!. But now I’ve got the problem how to color the water, and not the glass.
Ah! Thats more accurate indeed!
But now you have the same material applies to the whole thing?
Like one “liquid object” that has the shape of the jar?
If so…well… i have an idea but dont know if will work good…
You will have to apply 2 materials.
1 - the part that is not filled the glass material you have now
2 - You’ll make a single of this and then you will copy inside again change the color and mix with Fresnel as factor.
EDIT: Made a test it sort of works, as gives you the illusion that there is something there holding the liquid. You need to have different IOR to really see the difference between the water and the glass.
Yes! indeed. It acts like a thick foot base of the glass jar. Only one mesh object, with one texture.
And I love your solution! Adding a glass ring on top of it. Maybe the best approach 
In the sample below I added a seconds mesh object, just acting as water color, using transparency only.
But now it’s interfering with the glass material. It gets blurry. And the glass breaking index is changing.
And the glass distortion is gone (see post earlier).
Glass is tough stuff 
But I learn a lot!
My last try is to render two scenes and merged them in post composition.
The issue I was having with my solution was the I wasn’t getting ANY shadow from the glass or it’s contents so I changed the material a little bit:
About your solution will be really good if you use some DOF in the render this way no one will notice the water is blurry ahahah!
Must have some solution for this too…
But it’s really bad that the Transparent messes up with the refraction…
Edit!
Hold on… for me it doesn’t… maybe 2.8 has it fixed?
Did like this so you can really see where the transparent object begins.
So I created two scenes and merged them together in post-production. But then I forgot that merging glass cup with a straw and water color, also influences the color of the straw in parts outside water.
And then I discovered a mistake. I had given the water object two materials, a transparent one AND still a glass material. Bummer 
I dropped the glass material for the blue object. Tataaaa ! 
Thank you @capa14 for your support and work. I think we’ve both learned something today!
Everyday dude, everyday!
Congrats solving the issue 
Looking forward to see the “Jar filled with eyes” Scene
True! 
Good job!
Project file for download glass_jar-public.blend
Enjoy.
