There are certain settings in the Refraction and the General sections of the Corona Physical Material which should be used for setting up glass in different scenarios:
Thin Shell
- "Thin shell (no inside)" checkbox enabled - such material does not refract light and does not generate refractive caustics, which makes it render very fast. This mode should be used for very thin objects such as glass panes in windows, soap bubbles, light bulbs.
- "Thin shell (no inside)" checkbox disabled - such material generates refraction and should be used for solid objects such as vases, glass furniture, glass objects with absorption color, liquids.
You can find the "Thin shell (no inside)" checkbox in the General properties of the Corona Physical Material.
Caustics
When the "Thin shell (no inside)" checkbox is disabled, you can toggle refractive caustics. Note that enabling caustics will usually make rendering slower.
You can find the "Caustics (slow)" checkbox in the Refraction properties of the Corona Physical Material.
Examples
Windowpanes:
Left - "Thin shell" off; Right - "Thin shell" on. There is almost no visual difference when rendering simple objects like windowpanes, especially from a distance. It's best to enable the "Thin shell" option in this case, since it renders faster.
Soap bubbles:
Soap bubbles are very thin and that's why the "Thin shell" option should be enabled.
Solid objects:
Solid objects, such as vases, require the "Thin shell" option to be disabled so that they refract light.
Optionally, caustics can be enabled in the material settings and in Render Setup > Performance. This increases realism at the cost of render speed.
The same scene rendered with "Thin shell" option enabled. In case of solid objects this option must be turned off, otherwise the result is unrealistic since refractions are missing.