Related Clues:
- Flue problem
- Diesel discharge
- Platform ... or something that appears four times in this puzzle?
- Pipe buildup
- Coke product?
- Smudge on 49-Across's suit
- Dirty coat?
- First of log cuts combined with coal dust
- Residue from burning
- Carbon from burning
- Coal-dust originally choking German industrial city
- Deposited carbon
- Form of carbon
- Black powder
- Deposit in chimney