I want to create some glass test tubes with semi transparent fluid content of some different colors. I'd like to see through test tubes on ones behind. There should be no scene background (transparent) and glass should be semi-transparent. Output is RGBA PNG

I know I have to set Transparent checkbox in Render -> Film.
I found this for glass: how to render semi-transparent objects with transparent background as a png with cycles

I don't know how to make fluid content to be as realistic as possible.

It should be in cycles.

Is there any solution for light not only as world surface to have effect on objects?

  • 1
    $\begingroup$ Yeah, I think I see your predicament. The Holdout fix alone will not suffice in your case because it's not only the glass, but also the liquid that transparency rays must pass through. If Holdout is on the glass it knocks out the liquid too. I think there may be some trickery you can do with the Light Paths node to get around this - either that or use Holdout in conjunction with compositing, isolating both the glass and liquid, then recombining them. One of those things that seems like it should be easy but in practice is not so. $\endgroup$
    – Mentalist
    Jul 29, 2015 at 16:09
  • $\begingroup$ related: blender.stackexchange.com/questions/26286/… $\endgroup$
    – user1853
    Jul 29, 2015 at 17:22

2 Answers 2


I've tried to composite three layers: compositing

Glass material: glass material

Fluid material: fluid material

Not ideal, but the best output I achieved for now: enter image description here

I don't know how to make glass material brighter.

  • $\begingroup$ Very useful tip, no matter how old this thread. Thanks. $\endgroup$ Nov 4, 2019 at 11:27

It depends, if its only for still image, an easy way :

What i usually did, in mesh edit select the inner mesh of the glass. Shift D, copy it, P seperate them as 2 objects. Make the new object solid (close top).

Then assign two different glass shaders (tube and liquid object) You could use boolean substraction if you want it to be half full.


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