If anyone is interested, I just stumbled onto this blog entry by Calvin Tan, who paints the Alpine models figures : http://zyclyon.blogspot.com/search/label/Alpine%20Miniatures%20-%20SS-Unterscharf%C3%BChrer%20SSPzAbt%20101%201944
"The leather suit lends itself an aura of stylish class in contrast to most conventional combat uniforms. Its rendering too was not a complex issue as I soon got hold of how. The secret lies essentially in manipulating with both the satin and matt finishes.
A satin finish when compared to a matt one will have a deeper appearance. This attribute greatly enhances the illusion of depth when strategically applied within the deepest shadows. The satin finish was also extended to the mid-tones, creating the sheen of leather. This could be achieved by glazes of both oil paints and acrylic inks.
With the mid tones and shadows addressed, the highlights were rendered with glazes of matt acrylic black. Though most of my acrylic paints are tainted with Tamiya Flat Base I choose to incorporate with a little more than my usual dose into the black, producing a black chalky mixture. As a result, I do not lose any of the colour's properties and still get a tone light enough to contrast against the shadows.
Adding more dimension to the leather suit, effects of chafe and wear were applied along the edges of the suit. This lends itself more contrast to the suit, enhancing the crisp details of the sculpt."
He apparently got a painting guide published. Should be helpful!