The Collaborative International Dictionary of English v.0.48:

Unmantle \Un*man"tle\, v. t. [1st pref. un- + mantle.]
   To divest of a mantle; to uncover.
   [1913 Webster]

         Nay, she said, but I will unmantle you.  --Sir W.
                                                  Scott.
   [1913 Webster]