This does the trick, but in the wrong way, i.e. it creates a material and assigns it, but I want to pull a material from an existing library and assign it.
theMat = CoronaMtl ()
theMat.colorDiffuse = color 117 117 117
theMat.levelReflect = 1.0
theMat.reflectGlossiness = 0.1
theMat.name = "middle_gray_(18%)"
$.material = theMat