How to make liquid's color intensity less, where the geometry is thinner? I created this ICE TEA. Now I'm after even more realism. I figured that the intensity of the liquid should be less, where the ice cubes are close to the glass, where the liquid is 'thinner'. How to achieve this effect? 

Currently The liquid is Glass BSDF with IOR 1.33. I tried to subtract (boolean) the ice cubes from the liquid, to actually create the liquid thinner or thicker in certain parts. Only it gives a terrible geometry on the top surface of the liquid where the ice cubes stick out. I will probably have to model this surface manually, to get good geometry. But I figured I must do it, since I need thinner and thicker parts of the liquid. But even then, will it work?

I will be pleased also if you can advise me on other ideas how to make this ice tea more realistic. I'm thinking for instance bubbles along the top edge where liquid meets the glass. Anything else?

Edit: Ok, I used the Volume Absorption node. It works to some degree - the liquid seems brighter where the ice is. But now I want to put a gradient on the liquid, so that it goes from bottom of the glass to the top. At the moment I have a gradient going left to right. See my node setup. I suspect I have to feed the coordinates into the Vector plug on the Gradient node, I tried Vector Mapping node with various settings, but no success. How to change the coordinates of the gradient, so that it goes bottom to top?
Surface Color and Volume Absorption

I see you still have a rather strong surface color. In reality, liquids are not really colored by light loss on the surface, but ligh loss within the material. You should leave the color of the surface shader white and use the color for the absorption. The gradient may or may not be needed based on your initial intent with it. Experiment with the density of the absorption.

Refraction and Transparent

I am not sure why you mixed these two shaders. You should get a better result with simply a glass shader.

For Full Realism

You should note that only one surface should be between the glass and the tea and that should be a third material, with an IOR of IOR-tea / IOR-glass. This applies also for the ice cubes. This also means that the meshes will not be manifold, but this is how the render will be most realistic.

These are useful to read:


fluid in a glass
Liquid / glass interface IOR and normals in Cycles
http://adaptivesamples.com/2013/10/19/fluid-in-a-glass/


Alternative Solution

You can use the ray length to calculate the correct absorption, but this was useful only before cycles volume shaders was implemented:


http://blenderdiplom.com/en/tutorials/419-tutorial-absorption-in-cycles.html