HP 7475A Plotter: Zombie Pens

Following madbodger’s recommendation, but finding no local sources, a bottle of Koh-I-Noor Rapido-EZE Pen Cleaner solvent arrived. It’s billed as a solvent & cleaner for drafting ink, not plotter ink, which seems like an unnatural restriction.

I’d previously tried refilling some fossilized pens, only to find that the ink simply won’t flow through a nib filled with dried ink. So the pens you’ll see here have refilled reservoirs atop nibs that don’t write.

Dismantling the Koh-I-Noor black pen produced this unsightly mess:

HP 7475A - Koh-i-Noor black pen parts

HP 7475A – Koh-i-Noor black pen parts

I pushed the nib out of the shell using a pin punch, pretty thoroughly crushing the tip in the process. The ink reservoir looks like some sort of fluff inside a plastic sleeve, with a hole left by the butt end of the nib and a crust left by the evaporating ink. I scraped off the crust, put the nib in a cylinder filled with solvent, and let it sit for a few days, after which most of the black ink had vanished.

I reassembled the pen with the blunted end of the nib inside the body and the reservoir flipped end-for-end, in the hope that would work better.

Trying a different tactic with a Staedtler green pen, I removed the reservoir, filled the body with solvent, and dunked the tip in a solvent bath:

HP 7475A - Staedtler pen - nib soaking

HP 7475A – Staedtler pen – nib soaking

After a few days, the body was still mostly full of solvent, so it’s not flowing freely through the nib. Perhaps leaving the nib in air would encourage the fluid to move outward, at the risk of drying the nib even more.

Refilling them with inkjet printer ink produced this:

HP 7475A - Koh-I-Noor 2 - Staedtler 3 - zombie pens

HP 7475A – Koh-I-Noor 2 – Staedtler 3 – zombie pens

Pen 2, the gray K-I-N trace, seems a bit pallid, likely due to using cheap black inkjet ink. Apart from that, it’s continuous and presentable.

Pen 3, the green Staedtler, remains in the land of the undead; its ink flows better than before, but not enough to be worthwhile. The demo routine writes the annotation first and those characters came out well enouigh.

The other two pens also carry refilled ink: Pen 1 = ceramic tip, Pen 4 = Staedtler fiber (which, judging from the cap color, started out as gray and has become much darker after the inkjet ink refill).

All in all, a modest success and I’ll try again later. Better, however, to refill each pen before it dries out, as with the two “good” pens.


  1. #1 by hexley ball on 2015-09-06 - 20:33

    I wonder if an invigorating scrub in an ultrasonic cleaner would help dislodge the dried ink? If you don’t already have such an animal, it sounds like just the sort of thing you would whip up for a CC column or two :-)

    • #2 by Ed on 2015-09-06 - 20:55

      I’d like to say it couldn’t hurt, but we use the ultrasonic cleaner for our glasses and I can see a pain point lurking somewhere in there… [grin]

  2. #3 by Simon davies on 2015-09-08 - 03:20

    One other thought for the green pen – how about applying a gentle vacumn on the nib side to draw the solvent through. I have a hand vacumn pump intended for bleeding air from brakes but which is used for all sorts of additional tasks such as this one.
    Hopefully this would draw the solvent through the dried area of the nib. Or maybe just increase the flow through the already clear areas!

    • #4 by Ed on 2015-09-08 - 07:49

      Now that sounds just crazy enough to work…

      Bonus: I’ve been meaning to build a vacuum table for quite some time, so I’d have another excuse for gutting dead dehumidifiers.

      I tried the Koh-I-Noor solvent on random ink spatters, of which I have many, and it seems to have not much more action than ordinary detergent. Which is to say, not much, particularly on the black inks. So I’m not convinced it’s actually doing anything down inside those nibs, beyond what you’d expect from a plain-water-and-detergent soak.

      The bag of defunct pens continues to grow as I work through the collection, so at some point I’ll do more tinkering; they won’t get much worse between now and then. [grin]

  1. HP 7475A Plotter: Refilled Pen Performance | The Smell of Molten Projects in the Morning