Related Clues:

• Schmutz on Santa
• Flue substance
• Pipe-bowl residue
• Stainer of Santa's coat
• Component of Japanese sumi ink
• Burnt-coal residue
• Target of a sweep
• It's black in a stack
• Chimney stuff
• Toner ingredient
• It should cover Santa
• Some particulates
• Pollution on some bricks
• Grate film
• Grate stuff?