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So I am making my first interior scene and I have made a coffee table but am struggling to make it less reflective. It looks as though it's a mirror and I just want to know how can I make it more transparent.enter image description here

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  • $\begingroup$ Try turning down the IOR by a small amount (1.150 seems right) $\endgroup$ – three is enough dimensions Feb 6 '18 at 21:25
  • $\begingroup$ What exactly does the IOR stand for and what does it control? $\endgroup$ – Akados Feb 6 '18 at 23:02
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    $\begingroup$ @Akados It stands for Index Of Refraction and it is a measure of how a transparent material behaves and interacts with light in the physical world. See en.m.wikipedia.org/wiki/Refractive_index $\endgroup$ – Rich Sedman Feb 6 '18 at 23:28
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I believe you've most likely got your Normals flipped the wrong way. This makes the surface behave like the inside of the glass and results in an effect called Total Internal Reflection when hit by light at a shallow angle - ie, it effectively acts as a glossy surface.

The solution is to edit the glass mesh (select it and press Tab to go into Edit mode), select all (A until the whole mesh is selected), then go to Mesh/Normals/Flip Normals - or press Space and type 'Flip Normals'. Once done, press Tab to come out of Edit mode. Your glass should now behave as it should.

To demonstrate this, here's an example scene consisting of a cube sitting above a plane with a Glass shader material, with a further plane below and a large doughnut above. With the correct normal this produces the following result :

normal glass

Note the subtle reflection in the glass as you would expect.

Flipping the normal (so it now points down) produces the following result :

bad normal glass

ie, it acts as a mirror. This is a result of the Total Internal Reflection due to the rays acting as if they are hitting a surface on the inside of a block of glass.


Note that a similar effect to swapping the normals can be achieved by using an IOR of less than 1.0. ie, changing the IOR to 1/1.45 = 0.69 would produce the 'correct' result, without flipping the normals as the glass would then behave as its inverse; instead of being a 'block' of glass surrounded by air it would behave as a cavity of air within a block of glass (ie, as if its normals were pointed the ‘wrong’ way).

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    $\begingroup$ Thank you for your amazing answer Rich! Really helped :) $\endgroup$ – zyroz Feb 8 '18 at 20:36

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