| Factors | Levels | ||
| Low −1 |
0 | High 1 | |
| A: Concentration of KOH [M] | 8 | 10 | 12 |
| B: Temperature [˚C] | 40 | 50 | 60 |
| C: Relative humidity [%] | 85 | 90 | 95 |
| D: Time [days] | 7 | 14 | 28 |