Overview
In this tutorial I will examine a few different strategies for achieving a realistic skin shader in Cinema 4D. Skin has a particular quality that sets it apart from ordinary surfaces: it is luminously translucent. That means that in addition to the light that reflects off the skin's surface, light bounces around the layers of flesh below the skin, illuminating it from the inside. This effect is widely called "Subsurface Scattering", or SSS for short, and is a property of a number of translucent materials; wax, plastic, milk, and marble, to name a few. I will demonstrate how to quickly fake this effect using some basic shaders built into Cinema 4D. I'll examine Cinema 4D's native SSS solution, and finally, I willl show you a powerful third party shader that overcomes a lot of the limitations of C4D's solution.

Skin also has a number of imperfections such as freckles, moles, and veins. We can add these to our base color with the use of a Layer shader, and a couple of noise shaders.

In the color channel, click the triangle next to the Texture parameter, and select Layer from the list. Set the Mix Mode to Multiply, and then click the black preview square to enter the Layer shader properties.

In the Layer shader, click the Shader... button, and select Noise from the drop down menu. Click the small preview square next to the Noise shader, and set it up like the illustration you see here. We are using the Poxo noise shader, which looks like small disconnected patches of color. We will use this to create freckles. Take note of the color setup and the Low Clip setting in this example. You can make the freckles bigger or smaller using the Global Scale attribute of the noise shader. You can make the freckles more or less numerous by adjusting the Low Clip value of the noise shader. You can make the freckles more or less visible by adjusting the brightness of Color 2.

For the sheen, we are going to use a Fusion shader, combining Lumas with Fresnel to create a sheen at the edges where light is shining on the object. In the Luminance channel of our materials setup, add a Layer shader. We are doing this because, aside from the sheen, we are going to be using the luminance channel to add the subsurface scattering effect later. In the Layers shader, click the Shader... button and choose Fusion from the drop down menu. Click on the black preview square to enter the Fusion shader. In the Base Channel, add a Lumas shader and click the preview square to enter the Lumas properties. Turn off all three of the specular hightlights in the Lumas shader, and change its color to white. Set the parameters up like the illustration at the right.

Press the Up Arrow to return to the Fusion shader controls. In the Blend Channel, select Fresnel and change the mode to Multiply. Click the preview square under Fresnel and change the gradient to resemble the illustration at the right. As you can see, the Fresnel shader adds an edge sheen to the material. The Lumas shader controls this edge sheen so it only appears on areas that are illuminated by direct light. This will prevent our skin material from glowing in the dark.

The first of the SSS techniques is a fake, using standard surface techniques to simulate some of the effects of SSS without doing any of the scattering calculations. It's the fastest technique, but not the worst in terms of output.

In the Luminance Layers shader that we set up when we added the sheen, click the Shader... button and select Colorizer. Set the gradient similar to what you see here. In the Colorizer shader, select Effects/Lumas. In the Lumas shader, turn off all of the specular highlights, and set the color and surface paramters to what you see here.

When you render the result, what you should see is a nice pink skin color. The Lumas shader set to Oryen/Nayer with a high roughness value works at a much lower contrast than the standard surface color shader does, so the effect is that the lighting on the skin tends to "bleed" past the illuminated areas. Colorizer takes this low constrast shading and changes its color so that it is redder in dimmer areas. This simulates, to a limited degree, subsurface scattering.

Skin Color Variation
There are two different types of melanin that contribute to the spectrum of human skin colors. Pheomelanin is yellow-red, and is the type of skin pigment seen in Northern Peoples. Cumelanin is brown-black and is the type of skin pigment seen in African people. All other skin colors are based on various levels of these two pigments. I have prepared a Cinema 4D file (v 9.x) which has setups for a variety of these skin types. The color control I set up in the file is based off this theory of skin color—you can directly vary the relative percentages of pheomelanin and cumelanin, and their individual color intensity. I should also note that the darker the base skin color is, the less effect subsurface scattering should have on the final skin color—I have modulated the value of the SSS effect for each skin type.

Northern people, and North American aboriginal people have no genes for the production of cumelanin. Their skin color is derived solely from the reddish type of pheomelanin and its relative density in the skin. Asian people have very little cumelanin, and their skin color is determined by the yellowish type of pheomelanin. African and Middle Eastern people are colored predominantly by cumelanin, and so on. I used this information to arrive at the color settings in this file. Please feel free to experiment further.

This file does not need the VReel Skin shader—I used the fake Lumas technique instead so people without the plugin would be able to use it. I do encourage you to check out the VReel Shader though - it is worth every penny.

Click on the image below to download the setup file.