Keeping this simple: In Adobe Lightroom, the sliders for noise reduction give the smooth plasticy look. The luminance noise slider creates the effect far more than does the slider for damping chromatic noise. Warning: the smoothing effect can easily be overdone, so be judicious with it. It's most creepy when overdone on people; you can get away with a bit more on nonhuman natural subjects, and more still on manufactured things.
There are fancier techniques that create layers in Photoshop, which separate luminance variation, from chromatic variation. You then blur the chroma layer(s) sufficient to achieve the smooth skin tone you want, while retaining all of the skin's the textural clarity in the luma layer. There are how-to's out there (Google them). I don't use them enough to write a good walk through, but others have made great how-to's. Unlike the noise sliders in Lightroom, this effect creates some extremely high-end images, used in ads to sell make-up and anything in the fashion world. They can give the subject the skin tone of a 10-year-old, while retaining all the texture that makes the photo look real. In comparison, the plasticy look from luma noise smoothing always looks unnatural.
Canon EF 100mm f/2.8L Macro IS USM
- it is one nice lens. I cannot claim to have made equally looking shots with it, but it tends to deliver that sort of crisp, saturated look IMHO. \$\endgroup\$