The ink pigment, water resistance, light resistance, does not fade. For example, books, important documents signed will be asked to write clear, not easily fade. Now, many companies have launched the "exam-specific", in fact, it belongs to the "file private gel pen" in this category, you must use pigment inks. However, higher costs due to pigment inks, most of the manufacturers will be replaced by dye-type! So, when you purchase this special gel ink pen, be sure to choose big brand products and focus on their products is "pigment ink" professional identity.