Darker because of soot or dirt.
This word makes people think of things that are dirty or not clean.
Examples:
The fireplace is sootier than the rest of the room.
The cat came home sootier than when it left.
The sootier the chimney, the more dangerous it is.
My hands are sootier than yours!
After playing outside, my clothes were sootier than ever.
The more I touched the wall, the sootier it got.