re-silver       
verb [ T ] (also resilver) uk/ˌriːˈsɪl.vər/
 给(镜子)重新镀上银色物质
to repair a mirror by covering the back of the glass with a new layer of silver-coloured material
  Experts say that you should never re-silver an antique mirror because doing so will devalue it. 专家说绝不要给古董镜重新镀银,因为这样做会使它贬值。 
 Don't try to re-silver a mirror yourself; get a professional to do it. 不要试图自己重新给镜子镀银,要找专业人士来做。 
  - More examples
 - We specialize in repairing mirrors of any size, including silvering and resilvering.
 - You need to weigh up the cost of replacing the mirror versus re-silvering it.
 - They can re-silver the mirror or, if it's broken, they can try to replace it with an old mirror plate from the same time period.