View Full Version : Dielectric question

09-02-2009, 08:22 PM
I am struggling (still) with making good looking glass. An obstacle right now that I don't understand is that when using the dielectric node for the surface of a bottle, anything inside the bottle comes out black as if light was not transmitting through the surface. What am I missing?

As a simple example I have a scene with a bottle (poly inside and out) set to double sided and the default dielectric node with a small amount of absorption.

The rest of the scene is the default with a distant light only. I do turn on shadows, transparency, refraction, reflection.

If I place an object half inside the bottle and half outside the bottle (for comparison) the half outside the bottle looks normal but the half inside the bottle is almost solid black.

Also any really good glass tutorials out there that use the dielectric node?


09-02-2009, 08:36 PM
Don't use Double Sided with Dielectric.

09-03-2009, 02:28 AM
Dielectric works with "thick" geometry, just a poly with "double sided" does not work.
Also you have to use "spot info" and "switch" nodes for polygon side and a "standard" material node replacing the formerly needed "air" polygons (and you have to turn on "double sided" btw). For the "black" problem: check your refraction settings, what is going to be seen by refraction rays and the absorption value.
(I'll post a setup screenshot shortly)

09-03-2009, 02:58 AM
ok, that would be a basic setup for glass-like surfaces using dielectric:
Geometry has to be "thick", "double sided" is on, "standard-air" is diff, spec, refl = 0, just refraction index has to be 1, "dielectric" uses your "glass" settings with your wanted refraction index.

09-03-2009, 10:31 AM
But I thought with the dielectric node you did not have to do all that air/glass poly thing anymore ?

09-03-2009, 10:34 AM
But I thought with the dielectric node you did not have to do all that air/glass poly thing anymore ?

v9.3 and up you don't.

09-03-2009, 02:03 PM
You don't need doubled geometry anymore, you do the refraction index switch with nodes.
To achieve physical correctness, you still need to tell LW when to bend and when to unbend light rays passing through glass-like materials (or just materials with different refraction indices).
"Double sided" allows LW to "see" the backside of a polygon, the switch node setup tells LW how to bend/unbend the light.

And sorry, I forgot to mention that Transparency amount for the "Standard-Air" Material is of course 100%.

(@ sublimationman:
For your "black" problem: If you use the standard scene, the environment is black so I would assume that, if dielectric refraction settings are the default "raytrace and backdrop", it's the black backdrop that gives black refraction.

and OT:
just in case, you didn't read it already elsewhere: Snow Leopard ships with an older version of Flash Player which is vulnerable, so Snow Leopard users should upgrade
http://blogs.adobe.com/psirt/2009/09/flash_player_update_and_snow_l.html )

09-03-2009, 03:59 PM
No.. you don't...

As of LW 9.3 (ish) they introduced a feature known as volume stacking, which detects the back-sides of polygons and re-sets the IOR to 1.. without having to use the double sided/air polygon/air node tricks etc.. Just make a regular thick object (with a facing away back face, or it will go black) and add a standard dialectric node.. simple!

09-04-2009, 04:46 AM
you really got me! :agree:


09-04-2009, 05:52 AM
Yeah I think a lot of people have been confused by the new feature because they have been using the various hacky tricks of the past, not realising that all you do now is... nothing! :)

09-04-2009, 03:11 PM
It's always hard to abandon a vice ;)