Special pens with a novel filling system
Models 2 and 20 are ‘flat-top’ pen that will please anyone who prefers a large ink capacity and an interesting filling system. They are also beautiful and comfortable pens that will satisfy you even if you don’t need those things!
The combination of Schmidt nibs and ebonite feeds give a very smooth and wet writing experience, and you can keep an eye on the ink level both through an ink window in the section or by inspecting the ink reservoir directly.
The system
The filling system of Model 20 consists of a spiral-formed flexible bladder and a captive twist and push knob. To fill the pen you unscrew the blind cap which acts as the knob and when it is fully extended the further twisting will engage a second set of threads that allow the plunger to twist and compress the bladder. The twist motion is only half a turn and is very quick and the system will feel entirely natural the very first time you use it.
Each compression of the bladder expels air via a breather tube and the relaxation of the subsequent untwisting of the bladder takes in ink. One twist and release will take in about 0.5ml, and multiple twists can fill the pen with a generous fill of up to 1.9ml.
The bladder is 3D-printed from a very flexible TPE plastic that is robust and will last for many, many years. It is not at all like the latex bladders of old.
Size and heft
The Model 20 is about the same size as Model 10, but is heavier at 30g compared to 20g (18g and 16g uncapped, respectively).
The grip of Model 20 is, like the other Platypus pens, generously long. The Model 20 grip goes from 10mm at the narrowest up to 12.6mm just below the capping threads. The grip is both micro-textured from the 3D printed layer lines and subtly macro-textured with shallow helical grooves.
The filling mechanism of the Model 20 is probably more complicated to describe than it is to use. It is a reimagining, modernisation and combination of two filling system components from the last century: the twisty-fill bladder of pens by several manufacturers and the captive blind cap of the Stephens ‘button fillers’. I have previously written about the old latex bladder twist fill pens in my blog here, and you can expect a blog post about the Stephens pen and its system once I have finished researching it.
Instructions for filling the Platypus Model 20 fountain pen
To operate the Platypus twist-fill system you simply rotate the blind cap in a clockwise direction (it has a left-hand thread) to extend it into the working position and insert the nib fully into your ink bottle in the normal way. Twist the blind cap by a further half turn to twist and compress the bladder, and you will be rewarded with bubbles in the ink. Release or untwist the knob and the pen will suck up ink. Repeat the process until air bubbles stop coming out and your pen is full. The first twist is usually good for nearly half a millilitre of ink, and a full fill is a very generous 1.8 millilitres. When the pen has as much ink as you like, wind the blind cap back down the thread and dock it with the end of the pen body. Wipe the nib and feed in the usual way and you are ready to write.
The photo shows a pen with the blind cap in the extended position. Notice the left-hand threads on the plunger rod (dark grey) and at the end of the blind cap liner (light grey). The plunger rod is removable and replaceable, but tests have shown that it is very wear-resistant. There is a 3mm stainless steel bolt inside the rod, so it is plenty strong.
To empty the pen you can either write it dry, or simply do almost the same as for filling the pen. Because of the breather tube there will be a mix of air and ink expelled each time you operate the system. Slower twists will increase the amount of ink being expelled each time relative to the air (because of the resistances of the air and ink paths and the relative viscosities of air and ink: ask me if you want a long explanation!). Make sure that you have the pen arranged so that the nib faces downwards because the ink channel is along the top of the feed.
The twist-fill mechanism makes it easy to rinse the pen with water or pen-flush solution and you can unscrew the body from the section to expose the bladder and see how well you have done. Occasionally a drop of ink will remain caught at the top of the bladder, waiting quietly to contaminate the next colour of ink you load. You will be able to see that ink if you have taken the body off the pen. Any mischievous ink can be readily removed by simply inverting the pen once or twice during the as you rinse it out.
The Model 20 bladder is driven by a crown-shaped piston that has teeth around its upper margin which engage with dimples on the top of the bladder to allow the twisting and compression forces to be transmitted. There is a clearance between the top of the bladder and the piston crown so that you can unscrew the body from the pen without squirting out any ink. That means that you can fully expose the bladder and ink reservoir at any time, and you can even operate the bladder with your fingers instead of using the blind cap. That can sometimes be useful while rinsing the pen, and for filling if you really, really must maximise the fill volume.