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There are many references related to the physically-based rendering of several natural features of the numan body, such as skin, hair, eyes.
However, I could not find specific information about the simulation of visually realistic nails. For example, I did not find specificities of the characteristics of the reaction of human nails to light.

Image from the Wikipedia article

A few ideas I had:

  • According to the Wikipedia article, nails are "made of a tough protective protein called keratin. (...) It is made up of dead skin cells".
    Hair is also composed of keratin, so nail rendering might have a few similarities with hair rendering? However I think the main feature of hair rendering is the coloring of specular highlights due to internal reflections inside the hair fiber. Is that phenomenon significant or does it even happen for nails?

  • Examination indicates that nails are transparent and that they host sub-surface scattering effects. Are there models combining these phenomenons?

  • The proximity to skin also seems to suggest that the skin under nails has singular appearance properties. Should this layer require some specific techniques to be simulated too?

What kind of technology would be involved to simulate accurately the rendering of human nails?
What kind of tricks digital artists use to simulate the appearance of human nails?

wip
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2 Answers2

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I'm not aware of any rendering technology designed specially for fingernails. Just eyeballing it, I would suggest that a combination of subsurface scattering with a relatively smooth glossy specular surface would get you most of the way there. In other words, you could use the same shader as you do for skin, but with different textures and different specular parameters.

I wouldn't guess that a hair shader would be too useful. Nails are not in the shape of fibers, nor do they have the kind of complex occlusion and shadowing that hair does.

That being said, if the scattering properties of the nails are different enough from that of skin, it might make sense to use a different shader (for instance, doing some sort of volumetric scattering instead of a dipole approximation). I don't know of any references on skin scattering that have investigated nails specifically, though.

Nathan Reed
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I don't know of any specific technology for rendering fingernails, but I agree that using subsurface scattering with some specular would be a good starting point.

A couple of things I'd take into account are that most natural nails without any coatings or nail polish aren't that shiny and have some ridges, so there should be some anisotropy to the highlights. I think a hair shader might be overkill for that though.

A few things I think would be interesting to look at would be things like inclusions from injury/disease/etc., discoloration, and varying thickness; there's probably some work to be done on how light scatters between the soft tissue of the nailbed and the nail itself. Another interesting thing to look at would be nails with nail polish on them; I bet you could do some cool stuff with car paint effects and long distance scattering (like with a backlit manicured nail).

Icetigris
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  • What Icetigris said, with the correction that although nails aren't always reflective, they have a high Fresnel constribution, especially on the tops of the lengthwise ridges. These ridges tend to be polished through normal wear, even if the valleys of the ridges are more diffuse. – Hanoixan Apr 20 '16 at 17:58