Hi Bill,

I have used this technique on a few cars and I like the effect.  I don't have any photos available right now, unfortunately. 

I tried it on six roofs at once and I was satisfied with two of the six attempts.  I tried a few with table salt (small granules) and a few with sea salt (larger granules); the table salt provided a much better effect.  The best color combination for the undercoat turned out to be a mixture of light gray with ~20% Testors aluminum mixed in.  Once the salt was removed I painted the seam caps with the original roof color and then weathered the whole roof assembly again with a little black powder to represent soot and dirt.  The addition of a weathered running board really adds to the contrast and overall effect.

Yes, it's my understanding (because Ed has told me this a thousand times) that the seam caps were not galvanized so they would hold paint better.  IMO the artist's objective here is subtle color contrast--contrast between the original roof color, the exposed galvanized surface, the weathered running boards, and the soot/grime overlay--all gently blended together.  

John Golden

Albersbach, DE