Rendering two plastic materials and one liquid on top of each other

[taiman]

Hello everyone,
compliments for your awesome forum, it really helped me a lot.
I am experiencing problems with my rendering and I hope that you will be able to help me.
I am trying to render a fountain pen made of transparent plastic and I am having two problems:
-1.- when the pen is closed with the lid, the plastic of the pen and that of the lid don't render well and the whole top becomes black, even though both of the plastics (pen and lid) have transparent qualities applied.
-2.- the plastic from the body of the pen, the plastic of the cartridge, and the liquid inside the cartridge present the same problem (the whole thing becomes black) when I overlap them.

separately they don't cause any problem, but when I overlap them they just don't render at all. please help me, I tried everything without success.

[taiman]

I am sure it's something really easy for masters like you. Thank you 

[Robb63]

Under the "Settings" tab, open up the "Advanced" options (if they aren't already).

Make sure "Global Illumination" is checked, and turn up the "Ray Bounces" until you get the results you are looking for.
Probably 10-12 should work, don't make ray bounces any higher than it need to be to get the look you want, as that will slow your renderings down a lot.

[taiman]

thank you it really helped! now it looks way better
I have another problem...(i hope it's the last one!  )

the problem with the lid is solved, but now the three layers (liquid inside the cartridge + plastic of the cartridge + plastic of the body) still don't render well, as you can see from the images attached (the first image is the total of the three layers, the second image is a detail of the first two layers)

thank you for your help, you're amazing!!

[PhilippeV8]

Also make sure 2 planes never touch in your CAD model.  Even if you separate them by 0.01mm, is ok !

[Arnaud]

Philippe is right.
You can either scale the components in your CAD, either use KS position tools to scale one of the component. A scale factor of 0.995 (internal) or 1.005 (external) should works.

[taiman]

ok the scaling works, everything is much better now, thank you.
i am now trying different settings to refine the rendering. i'll probably post here the final result.
thank you very much!

[PhilippeV8]

Please do !  (post final result) .. you got us curious now