Hello. I’m trying to understand how to use the shader but I’m a bit confused on a few things.

First, what is the average scatter radius of the epi and subdermal on humans? If my model is in correct scale, should the default 8mm and 25mm be used?

Second, the default epidermal color is quite yellow or orange (see attachment). I don’t think it looks much like bloodless skin and I’ve seen alot of grey/blueish epidermal textures such as this.

Does it depend on things like the light whether I should go for a orangeish or grey/blueish color on my epidermal textures or is one more correct than the other?

I’m using 3dsm 2012 if that matters.
Thanks.

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I’m not sure there is a one size fits all solution for skin setups, but there are some rules of thumb to work by, then tweak in a “if it looks good it is good” kind of way. Sometimes a setup will look great in one lighting setup, then look bad if the same model and material is in another.
The basic rules of thumb are outlined in this document.
Regarding the Scatter Radii, I do tend to leave them at default and focus my tweaks to the colouring of the maps at the various levels, then possibly tweak the Weights of the levels to get the balance right. For me this is not an exact science, but more trial and error to get the right look. It is very easy to over-do SSS and end up with a waxwork/latex look.
Rather than rely on just the colours of the skin levels, I like to map them. for the Unscattered Diffuse I will use a very desaturated map, in the Epidermal layer a not so desaturated or sometimes ordinary map. For the subdermal layer I compensate for the lack of colour with a very highly saturated map. I believe it is important to map the subdermal because that is where most of the colour comes from and the amount of colour varies across parts of the skin with density of veins and capiliaries, a flat colour won’t give you that. Although it may be more correct to do this by mapping the Weight of the subdermal.

In the example shown I’m not using the default SSS Skin Shader, but Zap’s Pluss version (it handles reflections better). Bear in mind this example is a Work In Progress, so it’s by no means the be all and end all of skin shading. There is much more to do on the actual model, the texturing and maps and settings for the skin shader, eyes, hair, etc… but it’s a fair start. It’s one of those things that you initially think looks good and fairly lifelike, then you compare it to your photo reference pictures, and it looks dead and fake. Recreating a convincing CGI human is very hard.
BTW, this is a continuation of this project which I started again with all new photos for a new model.

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Thank you for your reply, Samab, it cleared up quite a few things.

I see you’re not exactly using bloodless looking epidermal and it looks great. I had read in a few places that the epidermal map should look like the blood had been drained out of it. I think your example is rather impressive and much, much better than anything I’ve done. Thanks for those links and the pdf.

I’ve been wondering about another thing. On This picture, the red glowing line around the shadows below the nose is that possible with the sss fast skin?
This is not the best example I’ve seen, but it was the only one I found with quick googling which shows the effect I’m talking about. I have not been able to properly do something similar yet.

Thanks.

I see you’re not exactly using bloodless looking epidermal and it looks great. I had read in a few places that the epidermal map should look like the blood had been drained out of it.

Looking at it now I see I made a mistake, I have the original full colour map plugged into the epidermal layer, it was supposed to be the second partly desaturated colour correction of the map which I have in the reflectivity slot. I thought the render was a little too red, I was in te process of changing things at the time.
So yes, the top layers should not have much colour at all, the colour should come from below the surface. If you ever peeled off a blister or shed skin from sunburn, you know skin is colourless and translucent. The colour comes from the flesh and blood beneath the surface showing through the translucent skin. That is what should give that effect you asked about, you get a hard shadow on the surface, but light that goes through the surface is scattered and diffused in that red matter creating that softer more saturated edge. Though this effect may only be very noticable or obvious in certain lighting contitions.
But this is the sort of basic setup I would begin with, then tweak to refine, adjusting the weights and the colours of the layers until it looks right. I find the colour correction good for this because it’s more interactive than going into Photoshop and saving different versions for each layer for every little tweak. You see I’m only using a single source map at this point, in the end I will create separate maps for things like bump and reflectivity, and finish off the texture to get rid of that seam on the top of the head and a few patchy bits.