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Modeling the glass and liquid bodies with coinciding faces produces precision errors in the coinciding walls
Preview image by Xpert Mihai of www.maxwellzone.com
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This method has the disadvantage that makes the model setups very complex, less flexible and not suitable for animations.
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The "infinitesimal gap" method was the only way to ensure every ray enters and exits the mediums in the correct order
Nested dielectrics
The best way to overcome this situation is by using the nested dielectics approach. Using this approach, two dielectric bodies can overlap and the render engine can automatically "boolean" them in render time and remove the surplus volume leaving just one single polygon wall, and assign the proper material for that single wall depending on the direction of the incident ray.
This method works by putting the two dielectric materials in contact by priority order that you can define, indicating that when those dielectric bodies overlap, the renderer will automatically fill the overlapping volume only with the material of your choice.
The Nested Priority value is defined in the material basis and is set in the Global Properties level. The lower this value, the higher its priority, meaning that where a body with priority 0 and a body with priority 1 overlaps, the overlapping volume will be filled only with the priority 0 material.
The nested priority value is only taken into account when one material intersects another; when this happens, the position in the queue of priorities determines which material prevails over the other. So Maxwell will understand that in the intersecting volume, only the material with higher priority exists, generating the right index of refraction in the contact wall and disregarding the lower priority material in that volume. You can think that this works a bit like boolean operations where the material with lower priority (higher number) is removed in the intersecting volume.
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Setting the Nested Priority parameter of a dielectric material on the Global Properties level
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