This started because I like fineliners, I had a dim memory of experimenting with technical pens way back, and I like the many of the colours in Rohrer & Klingner's Antiktusche line. So, a few weeks ago, I got really interested in the possibility of using acrylic inks, which is what they are, in technical pens. (I like self contained pens instead of dip pens. Personal taste.)
By the way, technical pens or dip pens or whatever, go and have a look at those Antiktusche colours. I higly recommend not only Rohrer & Klingner's website, but the swabs at http://www.kalligrap...ntiktusche.html. If you live in Europe, you might then want to buy your ink there as well, to support them for putting up these helpful swabs.
First, I searched this forum for useful information. Unfortunately, you mostly get people who do not really read the question and then give you advice they have heard somewhere. In other words: You ask, can acrylic inks be used in technical pens, and people will give you categorical advice like, only fountain pen ink should bne used in fountain pens! Ah. Quite. The technical pen is not a fountain pen. Also: As I have since learned, even fountain pens can take acrylic inks, provided you are prepared for extra work and care. If you use old and / or expensive pens, it makes sense to take no rists. If you are open to trying some weirder things, mess around!
Second, I mailed both Rotring and Rohrer & Klingner. Rotring, unsurprisingly, will tell you that only inks made by Rotring are safe for their pens. If you used anything else, you void the warranty. Rohrer & Klingner will tell you that, in principle, their Inks are fine for the Isograph, the Rapidograph, even the Rotring Art Pen. The important bit is the "in principle". Those pens are designed with highly pigmented ink in mind, so that is not going to be your problem. The acrylic bit is going to make things risky. If acrylic ink dries, it stops being water solluble. So, if you let a pen dry out, you could end up with a solid mass which cannot be cleaned from your pen.
Third, I have begun buying technical pens from various manufacturers, and not all of them have arived, yet. I have also begun experimenting with a few of those Antiktusche inks. What I have not yet done is let a pen dry out completely and see what can be done with the cleaner fluids from either Rotring or Rohrer & Klingner.
Once all the pens I ordered have arrived, I will write something about how they compare. And sooner or later, of course one will dry up. So I will then post about the experience of cleaning it.
Bottom line so far: You can get some techical pens for under € 10. There is no reason not to play around with acrylic ink in a technical pen, even if you fear it will kill the pen eventually. You can do a lot worse with € 10, I am sure. Also: Acrylic ink, unlike fountain pen ink, turns out to be amazing for writing postcards, which these days are often very bad at handling fountain pen ink. I kave some cards which turn into an absolute nightmare at the first drop of even my best behaved inks. Acrylic ink works like a charm!
Thanks to Rohrer & Klingner, as well as RoyalBlueNotebooks and fiberdrunk for help / advice.