Multimaterial Workflow

Tips

Introduction

The MultiMaterial Workflow helps you assigning different materials to different parts of an object without the need to explode it first. This is mostly useful for Rhino that does not allow applying materials to selected surfaces.

Apart from that, this workflow is also essential for transparent objects which make this method useful for any other modeler too. An exploded object in Thea will always render with no refraction since it will not be considered as a closed volume, like in the following image.

In the following image, we used this approach to create different variations. All four models are exactly the same and the only thing that changes is the type of the material we create for each layer. The second object from the left combines a Glossy Layer with Transmittance and high Roughness and a second Glossy Layer set up as Gold.

We will be using Thea for Rhino since Rhino also supports Multi UVs that will come in handy later on for adding extra details to the final rendering.

What will we be doing?

  • Unwrap the object
  • Arrange surfaces in 2 different groups in the UV Map.
  • Transfer the UV Map to an image editor.
  • Create a mask by painting with Black & White over the two groups.
  • Create materials using the Mask texture.

1. Preparing the model…

We will be using a basic model of a bottle. In order to apply different materials to different parts of it, we need to unwrap it first using the Unwrap command. (Image 1) The UV Map does not have to be perfect as long as it clearly separates the surfaces that will be having different materials.

Now that we have our model unwrapped, we can use the UVeditor command to display the UV Map in the Viewport (Image 2).

2. Creating the mask texture…

As you can see in image 2, we have divided UV Islands into two different groups. The UV Map needs to be transferred in an image editor and the easiest way is to just use Print Screen since accuracy is not what we need for this mask right now.

After cropping the image, we will use black color for the whole image and paint with white, one of the group of surfaces (image 3).

3. Creating the materials…

For this one, we will need to create two layers, one on top of the other (stacked). The two layers will be applied to different surfaces of our objects based on the unwrapping and the mask image we just created. Optionally, we can add a 3rd Layer acting as dirt over the two. (image 4)

Image 4
Material without mask in the Layer Weight

TIP: As you can see in Image 4, both Scattering & Structure are active at the same time. You can do this by holding CTRL and Left-Click on the icons.

1st Layer (Clear Glass)

Let’s create a Glossy Layer and adjust it. For this one, I used the following settings (image 4):

  • Reflectance, Transmittance: 255,255,255
  • Absorption: 30,245,245
  • Absorption Value: 150
  • Roughness: 1%
  • Bump Texture: Used a noise texture.
  • Bump Value: 6%

2nd Layer (Frosted)

Now for the second layer. Duplicate the Glossy Layer we just created and move it above the 1st one. (image 4) Keep everything as is except for Roughness which will be increased to 35%.

If we now render our scene, you will notice that the bottle is using the 2nd layer (Frosted) and this is because we haven’t changed anything in the Layer Weight panel, that is now at 100% and is not using the mask texture we created earlier. (image 5)

Let’s go back to our material, select the 2nd layer (top) and click on the Layer Weight panel. In the Weight (%) parameter click on the texture button and load the mask texture that we created earlier.

Now that there is a layer mask in the weight panel, Thea will use the Black and White values to determine if the Layer below or the current layer will be visible. (image 6)

Black color means that only the current layer will be visible and vice versa. So, in our case, we used white color to the parts that we wanted to have more roughness, 2nd Layer Frosted.

3rd Layer (Dirt)

As an optional step, we will add a Basic Layer on top of the others but before we do that we need to add a second UV Channel with a different UV projection so that the dirt map can be tiled nicely onto our surface. (image 7)

With the object selected and the Texturing Tab active, we enable the “Use multiple mapping channels” option. For the bottle, a Cylindrical Projection was used.

Now, the tricky part!
There is a small difference between UV Channels in Thea and Rhino.

UV Channel 0 in Thea equals to UV Channel 1 in Rhino and so on. You can find more details in this Knowledge Base article.

So, let’s go and create the Dirt Layer.

We will add white (220,220,200) in the Diffuse Color and assign an image with dirt (fingerprints & smudges) in the Layer Weight Channel. We need to change the UV Channel from 0 to 1 and lower the Layer Weight percentage to 20%.

In Image 4 you can see how the Dirt Layer has been setup.

I hope this article helps you understand the power of the Material Lab but also the advantage of mixing layers to create different materials with the least effort.

Thank you for reading!