denigrate

To criticize so as to besmirch; traduce, disparage or defame.

Although in public Soviet officials tend to denigrate the French electric locomotives imported recently, there is little doubt that lessons learnt from these engines will be incorporated in new Russian designs.

To treat as worthless; belittle, degrade or disparage.

You have no right to denigrate people and things that you have no personal experience with.

To blacken.

Blackened.