OXIDES
| Date | Clue |
|---|---|
| 2020-10-11 | Lime and rust |
| 2020-09-06 | Rust and quartz |
| 2018-03-03 | Lime and others |
| 2017-05-17 | Laughing gas and rust, for two |
| 2012-06-04 | Rust and lime |
| 2011-12-29 | Rust and quartz |
| 2008-04-20 | Laughing gas and water, chemically |
| 2003-11-12 | Rust and lime, for two |
| 1997-09-24 | Some binary compounds |
| 1997-05-14 | Waste gases, e.g. |
| 1997-03-16 | Lime and others |
| 1995-05-05 | Rust and others |