Applying material to backfaces

Hi. I am trying to make an interactive sectioning mechanism. Until now it works great, but I want to be able to paint the backfaces of the object in a way that they can be perceived as a cross section. something similar to this:
[link text][1]

To perform the cross section, I use a material that is transparent or opaque depending on the position of the pixel on either side of the section plane. That works Ok.

It seems that UE4 completely discards the backfaces so no material can be applied on them whatsoever. Of course, I can set the material to be two-sided, but then UE4 flips the normal of the backfaces so I can not discriminate if the pixel belongs to a front or back face using the classical dot product of the normal at the pixel and the view direction.

As you can see in the image, I can get (1) or (2) depending on the two-sided setting of the material, but I am looking for (3), assigning a constant color to pixel that belong to backfaces.

any idea?

Solved… I discovered the TwoSidedTexturing material node. That makes the trick

Hi . can you share the method with one you achieve result 3?

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