Well, I think I've got a test piece that is showing some promise. I won't know for sure until 'the ink is dry' so to speak and if it turns out I'll certainly post my results and recipe.

By glaze I mean using a 'glazing' medium (similar to the matte medium) which is designed to be added to acrylic paint to make the layer of paint translucent allowing the underlying color to still somewhat show through. The glaze is similar to a wash, but is generally a little thicker and thus more sticks to the top rather than seeking the crevices like the wash does. In truth, I'm fairly new to all of these mediums and am still learning the 'real world' use of them. So far I'm liking the results though and hopefully the new test roof piece will work out.