Now as I said, when using refraction on a solid object, the MINIMUM useful raytrace bounce limit is 2. Without at least 2 bounces, your object appears black.

However, some important bounces happen from internal surface reflections. So you have a ray enter the glass (refract), bounce off an internal surface (reflect), and then exit the glass (refract). To make this work you must allow at least 3 bounces.

Compare this to the first and you'll see the difference.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)