Historical clue formulations

• Dirty coat — 2025-08-02
• Layer of filth — 2025-06-10
• Filth — 2024-06-21
• Dirty buildup — 2023-10-09
• Filth — 2023-04-18
• Dirt — 2021-03-21
• Dirt, dust, soot, etc. — 2017-06-19
• Dirty coating — 2016-06-27
• Soot — 2014-03-09
• Old machinery coating — 2012-03-25
• Smutch — 2007-08-05
• Dirt — 2006-09-12
• Sandblaster's target — 2006-06-30
• Scrub brush target — 2005-07-08
• Dirt — 2002-11-27
• Detergent target — 1999-12-28
• Tough laundry problem — 1994-12-11