Among fountain pen collectors, inks are as important as the pens themselves. In the past, bad ink has caused problems for fountain pen users, but today, most inks should work just fine. Fountain pen inks should be chemically stable, meaning not too acidic or alkaline, because this can cause corrosion and ruin the mechanisms of the pen. Most inks are made of color dyes, a chemically neutral thickening agent to control the flow of the ink, detergent or surfactant so the ink doesn’t clog, and a small amount of fungicide. Although today’s market includes pretty much any color ink one would desire, the traditional colors for fountain pen inks are black and blue-black, royal blue, red, turquoise, green, and brown. However, lighter color inks can tend to appear lighter when wet than dry. Be wary of the pigmentation of an ink, especially if you have pens with clear barrels. Inks with high pigmentation might permanently stain the plastic.
Although manufacturers suggest throwing out ink more than two years old, there is no chemical reason to do so. Vintage inks more than fifty years old are used today in new pens with no problems. Things to look out for in older inks are the evaporation of water and contamination. Fountain pen inks do vary in their flow characteristics. The amount of thickening agent used in the ink ensures the viscosity of the ink and can differ from brand to brand and from color to color.
An interesting tradition in inks is ink blotting paper. A blotter card is just some absorbent paper used to soak up any extra ink at the tip of a fountain pen. Most people like to get these for free and distribute them as business gifts. Hard-core enthusiasts also like to collect vintage blotter cards and go to extremes to ensure they stay in their original, un-blotted conditions.
Permanent inks are made to withstand light exposure better than washable inks. Although inks do tend to stain hands and clothes, they can usually be easily removed. Normal hand washing after two days should remove ink from skin, and a drycleaner can help with fabric stains.