Indelible

a.
  1. That can not be removed, washed away, blotted out, or effaced; incapable of being canceled, lost, or forgotten; as, indelible characters; an indelible stain; an indelible impression on the memory.
  2. That can not be annulled; indestructible.
    3. Indelible colors ,
    fast colors which do not fade or tarnish by exposure.
    Indelible ink ,
    an ink not obliterated by washing; esp., a solution of silver nitrate.