Historical clue formulations

• Lead-bearing ore — 2018-10-23
• Main ore of lead — 2017-09-19
• Lead provider — 2009-01-18
• Lead provider — 2005-04-01
• Ore used for old radio crystals — 2001-01-27
• Ore of lead — 2000-11-19
• Lead ore — 1998-01-20
• PbS — 1996-12-07
• Lead ore — 1995-06-09
• Lead ore — 1993-12-23