A Pentel Brush Pen hack.
Poor Pentel brush pen. It didn’t do anything wrong. I just wanted to see if I could use fountain pen ink in it.
I took off the white ring as instructed. Then I removed the stopper from the ink cartridge. (The cartridge is also the body.) The stopper isn’t meant to be removed; it’s there to regulate the flow of ink from the body to the brush.
It took some time to pump and rinse out the ink from the cartridge. I wasn’t that successful – while I squeezed the cartridge under water 23,954 times, black-tinted water still came out. (Squeezing out the ink isn’t a straightforward operation. The flow is very controlled, and there seems to be a second layer of material inside the cartridge.) I squeezed it one last time, plunged it into a bottle of Pilot Iroshizuku tsutsuji ink, and wondered what the result would be.
(Yes, the tsutsuji stained the paper label on the brush pen. It looks like rivers of fuchsia lava underneath black rock.)
Tsutsuji (fuchsia) + excess water + remnants of black ink = a serious, don’t-mess-with-me purple. As the excess water evaporates from the brush tip, I expect the lines to be not as watercolor-y, but more solid. I’m happy with this hack, and hope for non-bamboo doodles to come.
March 19th, 2010 at 11:58 pm
If you’re interested, there’s a Platinum brush pen that uses Platinum cartridges which you syringe ink into; a lot easier than this, methinks.
March 20th, 2010 at 12:20 am
Yes, there are! But this was fun to do.
March 20th, 2010 at 3:31 am
That’s so painterly! Wonder how it would work on rice paper…
March 20th, 2010 at 4:00 am
Very cool & inspiring experiment!
March 20th, 2010 at 4:59 am
Pretty. I hope to try this with mine once the ink is over
The (new) ink colour reminds me of Poussiere de Lune. 
I have syringe filled my Pentel Pocket Brush pen with that ink and it worked well.
March 20th, 2010 at 8:08 am
Nice description. I feel like I was there while you did this hack. Love the purple the way it is in the illustration. Very nice shading. Cool!
March 21st, 2010 at 1:53 pm
Nice post and pretty successful hack. Yet, I think I would probably go with the syringe approach first if I ever decide to recycle a brush pen ink cartridge.