Historical clue formulations

• Covers in a black powder — 2024-08-31
• Covers with chimney grime — 2021-08-20
• Blackens with chimney grime — 2012-08-15
• Blackens, in a way — 2006-09-05
• Covers with coal dust — 2005-02-27
• Covers with fine black particles — 1999-03-14