先介绍几个名词：
圆珠笔 = ball pen
自来水笔 = fountain pen
中性笔 = gel pen
书写介质 = writing medium
A ball pen that uses a writing medium with a viscosity between (that of) water and oil is called a gel pen. The gel pen, originated in Japan, has now become a new writing tool that enjoys international popularity. A gel pen combines the advantages of both the fountain pen and the ball pen. Writing becomes so easy and smooth with a gel pen due to the low viscosity of the gel and addition of lubricating agents to further improve its fluidity. It is a new generation of writing tool and replacement of your ball pen.
