Modern writinginks usually contain ferrous sulfate with a small amount of an acid; on paper they darken and bond becoming permanent.
现代写字用的墨水通常包括了硫酸亚铁和少量的酸；写在纸上，颜色会越来越深，且能保持永不褪色。
2
Printing ink, writing or drawing ink and other inks, whether or not concentrated or solid.
印刷油墨、书写或绘图墨水及其他墨类，不论是否固体或浓缩。
3
According to the principle of dialysis, writing time of different kinds of fountain pen inks on different types of papers were measured using newly researched and developed dialyzates.