# How to cancel normal maps effect through the glass?

Hi, this question might be tricky.
I’m trying to make a set of painting tools but with these jars I’m facing a problem.

You can see clearly on the green one that some paint inside is “rough”. This is because, inside, the paint has bumps, since I was meaning these jars as available to be also opened (I’m aiming to sell it).
But here I get of course the effect of the internal normal map also when seen from outside.
I’d like to be able to find out a workaround to make it visible only when seen from inside, but I’ve no idea about the how. I also get double reflections in the glass as you can see, there are 2 rectangles of light while the source light is 1.
The IOR of the glass is 1.450… and the Glass shader is just mixed with the Principled shader (again with 1.450 IOR). Simple material…

The last solution is to erase away the normal map effect inside but I’d like to keep it if possible…
Thanks

I’ve found a solution and I write it here in case someone else needs it…
I’ve just attached a Geometry node to the Normal map node, connecting “Backfacing” with the “Strength”. Because the backfacing gives the value 1 or 0 depending if the faces are pointing inward or outward, so this decides if the strenght of the normal is 1 or 0!. Throuhg the glass, I see the “back” of the faces, so yeah.
But I needed the opposite values because it gives 1 with inward and 0 with outward. So to invert the output of the Backfacing socket, after Backfacing I placed a Math node with Subtract “1”, and then a Math node with Absolute “0”.
It works!

2 Likes