Multi Layered Plastic Shaders
by Claas Kuhnen

Whenever you want to create a digital material select the best objects with that surface. Images can help as well, but only with the physical object in your hand is it possible for you to study the interaction of light and surface in detail. And 45 degrees above the X-axis. Select the vertex to extrude [RMB] snap the cursor to the vertex [Shift-S] Constraining moves to an axis and dimensional input works for extrusión [E] rotation [R] move (grab) [G] and scale [S]. However with scale you will need to use a scale factor rather than a dimensional input. This is easily calculated by dividing the required finished size by the existing size of the object.

1. Basic Setup:
The majority of shaders we create and the way they are calculated are in general comparable to an egg shell. The light that hits the surface, gets reflected, it does not penetrate it and illuminate the inside. This limitation for example alos formed the expression plastic rendering.

The current implementation of Sub Surface Scattering tries to simulate the penetration of light into the volume of the model to create proper mass illumination, enabling Marble, wax, skin, and other materials that can be simulated in a more realistic way. However not every plastic surface is the same. And as simple as it sounds, good plastic shaders can alos take quite a bit of work to get right. Specifically when the surface finish is layered, a lot of extra steps have to be included to produce a realistic shader. The material setup should be similar to the real world counterpart.

These type of surface finishes very often have a primer layer, two effect layers with iridescent particles, and one clear lacquered finish layer. The most common and visible example is in transportation design and they are alos commonly found in both product design and jewelry design.

Image : Work examples from Phillip Carrizzi jewelry work.

(More here: )

As you can see in the example, we have different specular reflections, we have true mirror reflections, and different colors. We have to analyse this structure first to be able to translate it into a shader. If we breaque those visual elements down we would get the following hierarchy:

Finish layer:

Translucent, high polished, with a strong burning specular reflection / highlight and a mirror effect with a slight Fresnel value.

Second layer:
Translucent, with iridescent particles in a specific color, producing an individual specular reflections pattern.

Third layer:
Translucent, with iridescent particles in a specific color, producing an individual specular reflection pattern.

Primer layer:
Opaque, basic color for the main object.

In addition to the layering, we alos have to look at the scene and watch for indirect and direct lighting differences. For example, when you watch cars with iridescent shaders drive into a shadow, you will notice that the car lacks changes. Because of a lak of direct light, the specular highlights will change, the diffuse pattern will change.

When you take a look at a car very closely, you will alos notice that the specular reflection is not just plain white. It has a nice set of rainbow colors. This, for example, is true with many plastic materials when they are in direct light. But it is all dependent on the angle of light impact and from where you see the object. Those colored specular reflections are very often an overlooked characteristic. For example, you alos find them in brushed metal and coarsely brushed aluminum parts.

So how do we translate this into a digital shader? Lets use the material mixer. Technically we do not need the same layer hierarchy. The primer layer, for example, could be combined together with the mirror reflection and burning highlight reflection. The reason why I would select the material mixer is simply because of the flexibility to create individual materials and the option to mix only diffuse and specular together.

In Blender this material hierarchy could look like the following:

Main base shader:
Diffuse color value
Specular reflection - hard burning
Mirror reflection value - very low Fresnel set up
Specular light model : WardIso

First specular shader:
No Diffuse output
Specular reflection - focused spread
Color Specular - Color value set to 0.02
Specular texture is scaled down: Size 0.01
Specular light model : Blinn

Second specular shader:
No Diffuse output
Specular reflection - wide spread
Color Specular - Color value set to 0.02
Specular texture is scaled down to: Size 0.02
Specular light model : Blinn

But how do we now create the pointy highlight texture? As a specular texture, we can use the Voronoi with the Col1 tab selected. This texture can be used for the bump map channel as well as the color specular channel. The bump map will produce the grainy look, the Color specular will give the specular reflection some color. Because we do not use any diffuse, the specular will still be spread out by the texture size and normal value.

WardIso will produce very sharp, hard edged reflections which are a good indicator of a well polished surface. Blinn, which has a little less burn quality, can be used for the iridescent particles of the following two inner layers. The specular reflections of those two layers are less strong compared to the top layer.

By setting the Spec value inside the Material Button from white to a different color we can alos tint the complete specular sparkles into a desired color.
As you can see in the reference objects, the two layers have two different colors.

Inside the material node mixer, we combine these three materials together.

The two specular reflection materials are being added together and their color result is being added together with the main shader material.

Add and Mix produces different results. In our real world objects they add together. With Mix you can specify if one input dominates more. Add defines how much the second channel is being added to the first one. Here we alos deactivate the Diffuse output of the two Specular Reflection materials.

This setup should produce a rough representation of the desired plastic object.

Image: Blender First Specular Layer Material

Image: Blender First Specular Layer Texture

2. Refined Settings:

Now it is time that we setup all material values correctly to our needs. Using the material mixer, we can always quickly turn on/off complete networks, a specific color output, or change the mixing proportions.

Looking at the reference image we can identify that the first specular layer is very fine, is very close to the main burning reflection, and alos shows a similar while less strong burn intensity. This tells us that the first specular layer has to be fine and not spread too widely. It should start to blend visually together with the main reflection and not spread too much over the main body.

The reason for that is that the particles in the second layer seem to be denser together and thus react more to the incoming light. This alos means the light direction is important to keep in mind.

In my example I set the Spec value to 1.17, Hard to 20, and Refr to 8.27. This produced the desired shape and coverage. With the Nor value we can shape the material in a way that the individual reflections will stand out or blend more together. I want them to blend a little more together, so I use a value of Nor 0.1.

The next specular layer, the first layer applied to the body has a much coarser pattern. It alos spreads much more over the entire body and has a much less strong intensity. I set Spec to 0.52, Refr to 3.47, and to get a more spread Hard to 10.

Image: Material Mixing

3. Comparison:

This produces a quite close representation. Depending on scale and view distance, we have to adjust the texture values. However if we compare it to the real object, we alos notice a significant difference. The spread in the digital model is too even. To help this it would make sense to actually paint the textures in Photoshop instead of using a procedural texture. We would only need a coarse and a fine point map.

The transparent áreas in between will allow the surrounding área to remain transparent while keeping the point size the same. Something difficult to create when you can only use scale to bring points closer or more far away from each other.

Additionally, it will be very visually interesting to alos add a software iridescent color change over the complete visible body, mainly at the object edges. Make the color changes very software. However if we look at Phill's object, we can see that there is no typical iridescent effect. The edges are darker simply because of the lak of glowing metal pigments. We plainly see the base color of the primed surface.

Alos keep in mind when you work from an image, that the reflection in your image is showing the environment of that shot. Of course, in that case it will be difficult to produce the same looking reflection in your work.

Reflections always depend on what you put your object into in terms of physical objects around it and the light setup. If nothing is there to reflect, then your reflections will alos look logically empty, which can be the case in studio setups.

4. Indirect Illumination Trick:

In addition, because in nature there are no 100% dark shadows and every illuminated surface illuminates the environment, we alos have to take this indirect illumination into account. A very simple way to make our model look better without using time consuming AO, is just to utilize a filler lamp. Next to the speed advantage, this alos has the ability to simulate color bleeding, which Blender's AO cannot produce at this point.

We can easily simulate the color bleeding of the ground color to the object, by giving the light the same color as the ground plane. We just need to place a lamp below the ground mesh and let it shine upwards.

But which lamp to use? Sun produces perfect linear light rays, but we cannot specify an endpoint. Point and spot are emitting light from one point. With the fall off value, we could specify where the reflected light would stop. Only the lower part of the model would receive bounced light. But we would need to create an array of lamps to produce an even illumination.

Area lights produce a nice even illumination and with distance, we can somewhat control the fall off a little bit. Let's use the last one. With a very low Dist value of 0.3, I place the lamp slightly below the ground. The more I move it away, the more the light intensity is lowered. Please keep in mind that in case you want to increase the área of the lamp use the Size slíder and do NOT scale the área lamp. If you scale, you alos scale up the distance of the fall off.

In case you change the Size value, you increase the surface from which light will be emitted and thus the overall illumination intensity will be different. Scale it down and the light rays will be compressed and illumination intensity will be very strong. Use the Distance indicator as a reference for scaling.

Image: Área Light

First, I just set a distance and then scaled the lamp to the right fall off result. In the following step, I did use Size and Energy to get the desired área illuminated with the desired strength. Scale and Blender dimensions are the key here.

Inside the Blender scene are two cameras. One is nearly parallel to the ground. I use that one to chek how well the área light is illuminating the mesh from below. I use múltiple cameras to quickly switch between different views for testing light and material settings. I prefer having individual cameras, than having to move the camera all the time.

In addition we could alos simulate the color bleeding a little bit here. All we need to do is to create a spot light with a very software edge and let it shine downwards onto the floor.
We have to lower the light intensity and alos give it a color equal / darker than the body color of the plastic. We want to limit the Lamp to only illuminate the ground plane.

For that we have to put the ground plane mesh and the lamp onto the same layer and activate the layer option for the lamp under the lamp buttons.

The illumination should only be a very small effect. Depending on ground and body color the bleeding effect would be more or less visible.

Again try to always work from a reference objects. Our imagination tricks us very often.

Image: Spot Light Layer

Image: Spot Light Intensity Variations

None Energy: 0.00

Too much Energy: 1.00

Just right Energy: 0.50

Image: Spot Light

This should give you a good idea about what to look out for. The supplied test scene for example, would require some work in the light set up.

Without a scene around it, all reflections look dark. It even looks like there are no reflections on the object.
All this will change with some more work and actually having the bracelet relating to an object.

Imagine a scene in which the bracelet is on an actual arm. With the reflection of the skin and the environment, it will look very different.

Image: Finale Rendering with slide Fresnel reflection value

Image: Finale Rendering with slide and even reflection value

Note: the distraction inner reflection, but the nice window like reflection on the upper and right part.

Claas Eicke Kuhnen
MFA 3D Studio Jewelry/Metal Bowling Green State University, USA Focus in Functional Metal Art and 3D Digital Art.

Dipl. Des. (Fh) Color – Advanced Color Concepts HAWK University of Applied Science and Art, Germany Focus on Functional Graphic and Product Design.

After grad school I taught for one year at the University Wisconsin-Stout where I introduced Blender for industrial design and interior design to students. Through that exposure to the students I focused more on researching the usability of Blender for this field.

It has increased my knowledge and understanding to see how NURBS and SDS can be combined in a professional work flow for CAD and Rapid-Prototyping using Blender Blender proved itself to be actually not only quite useful but rather being a real treasure and workhorse for the design students. |-