0. 50 liters. The magic pen is specially used to practice hard-pen calligraphy. The handwriting will disappear within half an hour and can be used endlessly. There are totally four scales on a pen, one scale is 0.25 liters, and the magic pen scale 2 is 0.50 liters. The magic magic pen is green, healthy, non-toxic and harmless. It adopts a lightweight design and invisible ink can be reused and added to it.