i) In case air does not enter smoothly

• If air does not enter smoothly from the back of the refill, ink will not come out from the pen tip. This is the same as a phenomenon in which water does not fall when holding on the straw containing water, because air cannot push the ink toward the pen tip.
• As shown in the photo above, push the sponge behind the refill toward the pen tip, and when the ink comes in contact with the ink attached to the sponge, the air going to the pen tip will not be transmitted.

The sponge behind the refill prevents ink from flowing out after the refill when air enters from the pen tip.

• If you put the pen into the washing machine accidentally, the ink of the refill may be cut off and become unable to write like the photo above. It is thought that the strong central force that moves the ink in the refill over several times from the pen’s tip to the opposite end of the refill during the operation of the washing machine. In such a state, the interrupted ink will lid and the air to the pen tip will not be transmitted.

The above picture is an example of experiment with oil ballpoint pen. When a strong force like washing machine works on refilling, sponge behind refilling will not prevent the outflow of ink and ink may leak out with sponge.