| Treatment 1 | control (without treatment) | --- |
| Treatment 2 | Leaching with cold water | 36 h |
| Treatment 3 | Scarifying with sand paper 120 mm | --- |
| Treatment 4 | Immersion in 80˚C water, gradual cooling imbibition | 24 h |
| Treatment 5 | Immersion in sulphuric acid 98% | 5 min. |
| Treatment 6 | Immersion in sulphuric acid 98% | 15 min. |