The Collaborative International Dictionary of English v.0.48:

Unscale \Un*scale"\, v. t. [1st pref. un- + scale.]
   To divest of scales; to remove scales from.
   [1913 Webster]

         [An eagle] purging and unscaling her long-abused sight
         at the fountain itself of heavenly radiance. --Milton.
   [1913 Webster]