Concentration of boric acid (%) | Pencil hardness (HB) | ||
PH PVA | FH PVA | M PVA | |
0 | 1H | 3H | 2H |
0.5 | 3H | 3H | 3H |
1 | 4H | 4H | 4H |
1.5 | 5H | 4H | 5H |