Skinning technique tips needed

[Panther_Gunn]

So, here's the thing.  I've got a rectangular object that's supposed to represent a tube down the middle, with curved flanges around it (more like bits of thick wire than solid sheets), so you can see the tube in the middle through the gaps.  I've represented silver material with just some basic silver lines on a black field, and an open tube-end surrounded by lines at the one end of the rectangle.  It's not great, it's not elegant, but it gets the idea across.  My problem is, now I need to represent the tube & wires as black -- obviously it won't work against a black background.  What would be the best way to represent the empty space between everything, or achieve the effect in a better way?  Images can be provided if I've not provided enough detail for a visual.

[Valandar]

Simple - make the lines in the refl map. Since lighter is more reflective, the darker shade on the "cracks" will give the illusion that they're deeper and thus reflecting nothing but themselves.