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EDIT NOTE: This thread had two question in it. One was answered, the the other was not. I split the question into to separate questions and the other one can be found here.


I want to animate cutting open a machine with a mesh with a boolean modifier (or something that does the same). And I want to colour the cut face.

What I want to create is something like this:

machine red cutface machine orange and silver cutface

In the animation I want to create, eg. the walls should be red, and other parts of it should have different colours.

This is actually what I want to get. An animation, then some kind of boolean modifier cutting away the mesh and the cutface has a different colour.

This video is a part the How It's Made show ( https://www.youtube.com/watch?v=6qnuQw3DFj0 )

I maybe think about this in the wrong way, but what I would like to have it that so I can specify that obejct X has has the matrial Y and if cut, the new face should be colour Z.

I can imagine how it could work: You could create a very thin layer over a mesh that is made up of a different material. So the coloured part is not really the colour of the cut face but the actual original mesh colour. The colour you saw before the cut is just the thin coat that serves no function.

As you can see in this prove of concept video ( https://streamable.com/5s6dv ), it would work up to some point. These are two cubes inside each other. The white one is a tiny bit larger as the red one (solidify modifier with a thickness of 0.01). The white cube is hollowed out using the red cube and a boolean modifier. However, as you can see in the end there seem to be some problems. Moreover, I think it's more like flub work, since you need an extra mesh that actually does nothing.

My Question:

If not clear, my questionis: How do I do this?

How can I add a colour to a cutface that is created with something like the boolean tool and can be used in an animation.

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    $\begingroup$ Why ask this again? Correct me if I'm wrong but isn't this the same question as the one you asked a few hours ago? Why not just edit that one with all the detail you put in here? $\endgroup$ – David Feb 21 '18 at 16:01
  • $\begingroup$ I use an image of the same scene, but if you would read it, you will notice very fast that it's not the same content. THIS request is about the cut face of a mesh. About how to apply a texture or a different colour to it. THE OTHER request is how to cut open a mesh in a very specific way. Yes, both origin from the same project, but both can be used without the other request. $\endgroup$ – Delta Feb 21 '18 at 16:27
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    $\begingroup$ Ok one is how to cut it the other is how to color the edges. $\endgroup$ – David Feb 21 '18 at 16:42
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This works out of the box with the boolean modifer:

  1. add your boolean modifier, don't apply it (this way you can use it in animations)
  2. add a second material, the one to be assigned to the cut-off parts
  3. change the order of the material so that the one created in 2. becomes the first material in the list.

This way, it will be assigned only to the cut-off faces created dynamically by the boolean modifier:

enter image description here enter image description here enter image description here

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  • $\begingroup$ fyi in this case the cutter object is a cube and has no material assigned to it. $\endgroup$ – Bruno Feb 21 '18 at 19:03
  • $\begingroup$ So Blender realises that there's no material assigned to the new faces and defaults back to the first material in the slots. I wonder if this brilliant solution was an intended feature or simply happened. I really like it. $\endgroup$ – Haunt_House Feb 23 '18 at 10:32
  • $\begingroup$ Indeed it seems like an unintended side effect ;) $\endgroup$ – Bruno Feb 23 '18 at 11:35
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Once you apply your Boolean modifier, you can go to the materials tab, add a new material with the plus icon on the right (do this for as many different materials you want to assign to the same object). Select the faces you want to apply a different color to, and with the desired material selected, click "assign."

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  • $\begingroup$ I want to use it in an animation so I can't apply the modifier. But by looking at the selected answer it's not far off $\endgroup$ – Delta Feb 23 '18 at 10:09
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I think a boolean modifier will apply the other object's materials to any parts it cuts from the modified object. So make sure that each cutter object has the right material applied, and it should transfer to the cutout. If you're wondering about UV mapping: that's not going to be easy here, but you can make a procedural material to do it instead or just use global coordinates for your texture.

I just tested the above: you do need to ensure that the cutter object's material is also present in the cutaway object's material list, but it works fine. No need to apply the modifier.

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