thick glass edges are dark

i have thick glass on a counter top At the corners where they meet, they show up as black per below. any suggestions? the leftmost blackline is at the corner. The second one is just at the edge of a piece of glass at an opening on the side counter. When viewed in sketchup, all these edges are clear. Appreciate any quick guidance

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Permalink Reply by Larry Goldberg on April 2, 2015 at 7:05am

thought the following 2 images might clarify. did a close-up render from a better angle. been playing around trying to make sure the safe finish was on all faces, no luck. here are two images - one in sketchup showing the clear transparent glass as modified by nxt and the sketchup model.

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Permalink Reply by Larry Goldberg on April 7, 2015 at 7:58am

Al....any chance of getting any guidance or insight?

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Permalink Reply by Rich Hart on April 8, 2015 at 8:02am

Try increasing the number of Refractive Bounces.

if that doesn't help, could you post a sample model for me to try here?

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Permalink Reply by Rich Hart on April 8, 2015 at 3:56pm

We played around with this and it looks like using the "thick" property of glass does not work well on glass where you can see the edges. The results are unpredictable, as you reported. Setting the Index of Refraction very low helped with the dark edges in some cases that we tried.

It seems to work OK using the Path Tracer Rendering engine, but does not work well with the Packet Mode rendering engine.

I would suggest either not marking glass as "Thick" where you have glass where you will see the edges of the glass panel. Or, if you truly want to get the Refraction through the panel, make sure that the edges of the glass panels are a different transparent material which is not marked as thick.

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Permalink Reply by Larry Goldberg on April 9, 2015 at 6:51am

Thanks Rich, alternate thin material helps a lot. Hopefully you can address edges of thick glass in the future.

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Permalink Reply by Render Plus on April 11, 2015 at 5:34pm

Thick glass can become quite interesting. Try lowering the Index of Refraction to get less distortion.

For example, we believe this is a photo of some thick glass and the edges are dark:

And we believe this rendering may be correct:

(This is from the nXt documentation)

And here is another photo example:

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Permalink Reply by Render Plus on April 11, 2015 at 5:40pm

You might try making the side faces "thick" to get some distortion when looking through the glass, but makaing the top and edge faces this, so they don't refract as much.

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Permalink Reply by Russell D. Houlden on April 11, 2015 at 7:42pm

This is an interesting discussion. I think that the top of the glass is light because of reflected light, not refracted light. If there was even a subtle light source ( even reflected light ) hitting the vertical edges of the glass, that would lighten those edges as well. I think that the edges are otherwise dark because the longer or taller a piece of glass, the darker the edges. Not all of the light that hits one side of glass makes it through, so even less along the length of a sheet of glass.

It's a nice rendering and when I saw it I thought it looked pretty realistic, except that the vertical edges would more naturally be reflecting some light, even if only reflected from other sources, so probably wouldn't be black. One of the things that I might try would be to increase the reflective property of the glass edges.