blacken

To cause to be or become black.

Iron and coal were the magnets that drew railways to this land of lovely valleys and silent mountains—for such it was a century-and-a-half ago, before man blackened the valleys with the smoke of his forges, scarred the green hills with his shafts and waste-heaps, and drove the salmon from the quiet Rhondda and the murmuring Taff.

To become black.

The sky blackened as the storm clouds rolled in.

To make dirty.

To defame or sully.

To cook (meat or fish) by coating with pepper, etc., and quickly searing in a hot pan.