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Render Issue: Material: Glass vs Clear Plastic

Question asked by Mitchel Palme on Jul 12, 2011
Latest reply on Sep 12, 2014 by Chris Daniel

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i am testing clear materials.

i have just noted that a "glass" material on an object took 57secs to render (800x600px) vs 37minutes for the same part in "clear plastic".

i would have imagined that the "clear plastic" has no or limited refractions and would have rendered even faster than the glass.

anyone else find this? any explanation?

i am also using keyshot. it has a material called "window" which uses limited refractions similar to a clear plastic.

as a side note, Keyshot to render the same scene, was about the same render time for the "glass" material in Photoview, maybe a little quicker but not much.

Mitch

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Ron Bates Jul 12, 2011 6:16 PM

Hi Mitch,

A number of things affect performance of rendering clear materials. Index of Refraction actually has a very minimal impact on render performance. The clear plastics we provide fall into 2 categories which result in them being slower. They either use some amount of fixed Subsurface Scattering. SSS has a dramatic impact on performance in any rendering system. Or they use a blend of real diffuse amount, and less than fully transparent which slows down ray traced calcuations. Glass, by default, will render as 0% diffuse and 100% transparent which is very quick.

If you truly want a clear plastic with no tricks, start with a high gloss plastic, set transparency to 100%, IOR to 1.0. and diffuse to 0. Save that as a custom appearance to re-use.

HTH,

Ron

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J. Becker @ Ron Bates on Feb 1, 2013 3:07 PM

I know this is an old post but for those who come upon it looking to speed up render time, this helped.

I ran with Ron's appearance, "High Gloss Plastic" tweaked, but didn't like the overall reflective qualities in the final render. With Preview set at better, the preview looks good but renders very different for me.

I performed a quasi-scientific test — a tooth-like object with engraving, re-rendered with the same resolutions, angles and lighting and image qualities. I tested out 20+ shifts of this appearance and compared them all to render times of all the clear plastics and clear glass. While the plastics and glass were over 15 mins for a best render, most of the "high gloss plastics" were under 2 minutes!

Here's what I ended up with:

High Gloss Plastic

Diffuse: 0 Specular: 0.9 Spread: 0.2 Reflective: 0.15 Transparency: 0.9 IOR 1.3

Clearer, more glass like: same but Specular 1.0 Spread 0.1 IOR 1.52 (duh). This render time is WAY less than 'clear glass'.

Hopefully this helps anyone out who searches the forum.

Jeff

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Chris Daniel @ J. Becker on Sep 12, 2014 1:59 PM

Hi Jeff

This may be an old post but I found it. Thanks for the info re clear plastics. I got a better result in a fraction of the rendering time. Thanks again for taking the time to share it.

Chris

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Ron Bates Jul 12, 2011 6:16 PM
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Hi Mitch,

A number of things affect performance of rendering clear materials. Index of Refraction actually has a very minimal impact on render performance. The clear plastics we provide fall into 2 categories which result in them being slower. They either use some amount of fixed Subsurface Scattering. SSS has a dramatic impact on performance in any rendering system. Or they use a blend of real diffuse amount, and less than fully transparent which slows down ray traced calcuations. Glass, by default, will render as 0% diffuse and 100% transparent which is very quick.

If you truly want a clear plastic with no tricks, start with a high gloss plastic, set transparency to 100%, IOR to 1.0. and diffuse to 0. Save that as a custom appearance to re-use.

HTH,
Ron
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- J. Becker @ Ron Bates on Feb 1, 2013 3:07 PM
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  I know this is an old post but for those who come upon it looking to speed up render time, this helped.
  I ran with Ron's appearance, "High Gloss Plastic" tweaked, but didn't like the overall reflective qualities in the final render. With Preview set at better, the preview looks good but renders very different for me.
  I performed a quasi-scientific test — a tooth-like object with engraving, re-rendered with the same resolutions, angles and lighting and image qualities. I tested out 20+ shifts of this appearance and compared them all to render times of all the clear plastics and clear glass. While the plastics and glass were over 15 mins for a best render, most of the "high gloss plastics" were under 2 minutes!
  
  Here's what I ended up with:
  High Gloss Plastic
  Diffuse: 0 Specular: 0.9 Spread: 0.2 Reflective: 0.15 Transparency: 0.9 IOR 1.3
  
  Clearer, more glass like: same but Specular 1.0 Spread 0.1 IOR 1.52 (duh). This render time is WAY less than 'clear glass'.
  
  Hopefully this helps anyone out who searches the forum.
  
  Jeff
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  - Chris Daniel @ J. Becker on Sep 12, 2014 1:59 PM
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    Hi Jeff
    This may be an old post but I found it. Thanks for the info re clear plastics. I got a better result in a fraction of the rendering time. Thanks again for taking the time to share it.
    
    Chris
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Render Issue: Material: Glass vs Clear Plastic

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