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I guess that answers my question then.

My post is just an explanation as to why you cannot use that 'overlaying' technique.....with an example of how you can 'see for yourself' how PS handles transparency, hopefully reinforcing your understanding of why you have these problem 'grey' areas.

I didn't offer an alternative, you seem quite capable of doing that yourself.

Maybe this helps...

[ATTACH]53543[/ATTACH]

(There are duplicate versions for display on the forum only, to allow for the forum themes.)

Download the above image and open it in PS.

With the MOVE tool selected hover over the mid-point of the upper and lower layer masks...it should be 50% Opacity. (Use the 'INFO' panel to monitor Opacity)

You'd expect then that the mid-point of the 'result' of adding those two layers together would be 100% (50% + 50% = 100%) but its not....its only 75%.

This is why you see 'grey' areas....the mask is NOT 100% Opaque.

Regards.

MrTom.