About our Clear Piston Demonstrator Pens

Our Clear Piston Demonstrator pens are see-through pens that you fill and empty using a piston device. This lets you see how much ink is left in the pen, what color you are using, and how the ink flows from the reservoir to the nib. They were originally made as a sales tool to demonstrate the internal operation of fountain pens, but they have gained a life of their own as an attractive pen.

Our Clear Piston Demonstrator Fountain pen measures 5.25" (13.5 cm) uncapped and 5.5" (14 cm) capped. You can't post this pen (put the cap on the back) because of the piston turn knob.


  • Beautiful pen - crystal clear. Check your remaining capacity and color ink at a glance.
  • Piston filling device - quickest and cleanest way to fill a pen to its maximum capacity
  • Gain access to the reservoir through the back of the pen so you can clean out dried ink.
  • Just two pieces - the pen and the cap.

Removing the piston filling device

There are two sets of threads for the piston, and they turn in opposite directions. Do not force anything. You are dealing with thin plastic in small parts. Instead, follow these three steps:

      1. Remove the piston
      2. Clean the pen.
      3. Reinsert the piston

The Benefits of Piston Demos

      • Use any ink — even India — or paint
      • Large-capacity ink reservoir
      • Keep your eye on the remaining volume
      • Draw all day and don't run out
      • Easy to clean
      • Replace the nib easily
      • Designed to hold the most popular large drawing nibs

Other Nibs You Can Use

      • Brause Rose nibs, including Bandzug and Ornamental
      • Crowquills
      • Gillott 303 — using our adapters
      • Hunt Drawing nibs, including the 22B, 56, and 101
      • Manga G nibs, including Nikko, Tachikawa, and Zebra
      • Principal
      • Sketch

Piston fillers are handy pens - no need to change cartridges when you run out or fill a converter, which can be awkward. Stick the nib into the medium and suck it up by twisting the piston knob.

The only problem is that ink (or paint) can collect inside the reservoir, plugging up the pen or wearing down the piston seals. But that's not a problem with an Ackerman pen. Disassemble the back of the pen to remove the piston and clean the reservoir.

Since the Demonstrator is a clear pen, you can usually see what's wrong from the outside. You can disassemble the pen to clean the insides of the pen and replace the piston seals. In most cases, the seals should last the life of your pen. The seals can wear down when ink dries in the reservoir and you continually drive the piston over the rough spot.

Solution: Leave your Demonstrator pen filled with ink, or empty the pen and flush it clean. This prevents ink and paint from drying out inside the pen.

Removing the Piston

To remove the piston, start by turning the knob at the back of the pen in a counter-clockwise direction to unscrew it from the back of the pen. There will be a bit of clicking towards the end. Don't worry and don't rush. Just click your way through until the knob is free.

Pull out the tube. You might have to spin it off the piston stem.

Remove the plastic piece secured in the back of the pen, which should now be exposed. Take the little wrench and pass the fork around the base of the plastic piece. Jiggle the wrench until it seats correctly.

There are flat sides (detents) on either side of the plastic piece that are designed to be gripped by the fork. Turn the wrench in a clockwise direction. Be careful! The plastic is soft. If you strip the detents, you can use pliers if you're careful. You can also use hand pressure if you get a good grip. It's best to start with the wrench.

      1. Spin out the plastic piece.
      2. Slide out the piston.
      3. Arrange the pen parts so you can reassemble the pen easily.

You can now clean the inside of the reservoir and replace the seals on the piston.

To remove the piston seals, work each seal off the piston. You can roll the seal out of the notch. You can also use a pick to lift the edge of the seal to get it started. A toothpick is good. Try to keep the seal intact and for future use.

These are DASH size # seals, made from silicone, are usually available at most well-stocked hardware stores. You can order softer seals online at McMaster-Carr or a similar industrial supply business. Or, you can use harder seals if you want to.

To apply the new seals, roll one onto the piston and work it to be back notch. Then, roll on the second one for the front notch.

Cleaning Your Pen

To clean your pen, first remove the nib and feeds from the front. Then, remove the piston from the rear. Run warm water through the body. Use a diluted solution of soap to remove any stains or ink stuck to the sides of the reservoir. Don’t use a brush unless you want to risk scratching the inside walls of the reservoir. You can use a Q tip dipped in soapy water to try and remove dried ink.

Reinserting the Piston

To reassemble, reverse the steps for removing the piston. Begin by sliding the piston into the pen body. Then, screw in the plastic piece. Make sure the stem of the piston slides into the slot in the piece.

Use the tool to seat the plastic piece. Just give it a short quick movement over 10 to 15 degrees, and you should feel the plastic piece seat. Give it another short movement, and that's it!

If you don't seat the plastic piece correctly, it will start to spin out when you spin the knob back on. If this happens, reseat the plastic piece using the wrench and keep tightening it until you're sure it won't tighten any more without damage to the pen.

If the wrench slips and no longer grips the plastic piece, gently use pliers.

Slide the tube onto the piston shaft. You might have to guide the tip through a slot in the plastic thing. Spin the tube to grab the piston shaft. Make sure you can slide the piston back and forth. Push the piston all the way into the pen.

Screw the knob back onto the plastic piece using a clockwise direction. Keep spinning until the knob starts to bind. It should pull the piston back towards the rear of the pen. Keep turning the knob until it is flush with the back of the pen. You should feel several clicks.