UPDATE: July 20th, 2012
Friday! Woo hoo!
This update covers a couple of stages. First: gray misting.
I used my Winsor & Newton liquid mask to outline the areas that received the
gray misting. Then I used tape and plastic wrap to mask the entire helmet, leaving
only those small areas exposed.
The idea is to apply the gray while allowing some silver to show through in places.
Here's the dent area.
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This is that large damage area on the back of the dome, as well as some of the smaller
chips, too.
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Once that was done, I went back with a size 000 brush and picked out the silver chips
that were within those misted areas.
The dent again.
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The back of the dome.
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Finally, a smaller area above the killstripes.
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Next will be to add the really small chips and scratches with a sharp compass point.
After that, it's on to the mandibles! 
