Re: Why does the clear ink in a UniBall Fusion pen turn black when it is used?

Mary Helen,

Sanford's Uniball Pen actually has a ballpoint pen ink inside just like 
all other pens, except they have separated the ink into two parts:  
colorant and vehicle (water solution).  A typical ink for a ballpoint pen 
consists of color (usually pigments, but can be dyes as well), and 
a "vehicle" that carries the color (mainly water or sometimes alcohol).  
The vehicle may also have other ingredients in it to help preserve the 
ink, or make the ink slippery, etc.  What Uniball has done with the fusion 
pen is remove (separate) the color from the rest of the ink.  The rest of 
the ink is thus clear (not colored) and is what you see in the back of the 
pen.  What is not easily seen is the small "reservoir" of color that 
resides between the point and the vehicle.  As you write with the pen the 
vehicle flows down through the reservoir and mixes with the color just 
before it comes out the tip...