Can You Print With Highlighter Ink?

With huge swathes of people either out of work or working from home, many are now attempting all manner of exciting or silly projects in their downtime. [Emily Velasco] is no exception. She decided to explore the feasability of printing with highlighter ink.

It’s a messy business. Wear gloves.

The hack starts with a rather ancient inkjet printer, so old that it works with tractor feed paper. [Emily] set about gutting several highlighter pens and squeezed out the ink reservoirs into a ladle. The printer’s ink cartridge was then filled with the fluid, and a test print was fired off. Upon initial extraction, it appears blank. However, with the aid of a UV light, the printed pattern is revealed. It appears that the inkjet is printing a very faint image, such that the system almost works as an “invisible ink”.

It’s a fun little hack with an old printer, made easier as it lacks the DRM of newer models. It’d probably be quite achievable with a dot-matrix, too. If you’re similarly tinkering in the innards of your peripherals, be sure to let us know. Video after the break.

30 thoughts on “Can You Print With Highlighter Ink?

    1. That would be a plotter, but an excellent idea for (mostly) kids :0).
      – and It appears Crayola made one back in 1985 (“microcomputing-magazine-1985-04” will take you there).

  1. Aside from the DRM cartridge problem, I think this only would work on those old thermal bubble type inkjets, not sure the piezo ones would like random inks so much.

    1. There was a little discussion about this on Hacker News (where it got shared a couple days ago). A few people were saying that the piezo ones would probably work better than thermal ones, but they didn’t explain why. Maybe I should find a piezo printer and give it a try.

      1. I am going on info from a print article I read over a decade ago I can’t remember where. It may have been a piece to talk up an alternative inkjet tech. Anyway, what I got from that is that thermal style can be conventional water based, but the piezo ones need polymer inks that can be charged so the spray pattern can be tightly controlled. I think the piezo drive rather than the thermal is more a result of wanting to electrostatically control the droplets, resulting in inks that don’t react well or enough to heat. So it’s not that it’s piezo driven, it’s the reason why it was piezo driven is the problem.

        1. Nah, piezo heads use little mechanical piezo-actuated pumps. No charge is needed.

          Are you sure you’re not confusing that with the really old, first-generation inkjets? They used gasoline and carbon black (!!!!) as ink. It would be constantly sprayed in a jet in the direction of the paper, and was given an electric charge. An electrode plate near the ink nozzle could selectively repel the stream of ink, so it would divert toward a gutter and be recycled back, or else it could hit the paper, which was constantly moving back and forth, then up.

          The static charge / diverter method was used just because it was a nice quick way of controlling ink flow, rather than using some big clunky 1960s solenoid valve. I dunno what use they actually got, you wouldn’t see them outside a “shop” with it’s own computer room, and probably only in specialist applications.

          Anyway… that’s the only kind of electrostatic inkjet I know of. Nothing to do with piezos.

          1. interesting, I’ve seen a similar setup for package labeling. ink jet going into a gutter, electrostatically the jet is moved, but it uses ink and mek instead of carbon black and gasoline.

          2. The tech I’m talking about is from the 1960s. When did you see the package labeller working? I’d be amazed to hear it’s still in use. I can imagine it’d be good for bar codes, needing only vertical stripes, printed as the package moves past. For letters etc you’d need to move the package or else the jet accurately in 2 dimensions.

            I suppose one advantage it has is robustness. No microscopic pumps or heaters or plastic parts to fatigue and snap. The only moving parts are the ink and paper.

            I remember reading about it in books on computers as a kid. Back then the commercial office inkjet had only just been invented (late 80s), so books that were a few years older would mention “inkjet” printing as the huge chunky gasoline-spitting thing. Apparently the results were very good though.

            Yeah the carbon black / gasoline I think was just to meet the requirements of holding an electric charge and being black, was presumably the best they could come up with in an engineering lab that wasn’t geared to complicated chemistry, and probably not educated in that field either. What is “mek”? I suppose they’ve had a few years to work on the ink since then.

    2. I would have thought the opposite – bubble-jets rely on the ink being heated past it’s boiling point and not burning or suffering another undesirable chemical change, but piezo’s are just tiny mechanical pumps and should work with any fluid with a low enough viscosity…

      1. Speaking of viscosity, I found that the highlighter ink was a lot more spattery than the black ink, so teeny tiny droplets of it ended up all over the page outside of where it was supposed to be. I’m going to try and mix a little gum arabic into the ink to see if being a little more viscous helps with that

    3. Piezo will print almost everything as long as it’s not full of particles in the size range that would plug up the actual nozzle. Bacteria and other sensitive stuff is printed with Piezo. Not every “ink” responds well to being vaporised and shot out.

    4. Piezos are OK with most inks. Many years ago, we used custom (food safe, edible) ink made by a lab to print on modified EPSON inkjets. It was not that challenging but it took some trial and error. Conductivity is also an issue, if too high the injectors will eventually fail. For thermal ones it’s a different story, it needs to meet all these specs but also have a specific boiling point.

      As a fun side note, these EPSON A3 printers were modified to print continuously using external ink tanks. A microcontroller connected in place of the original keypad simulated the mandatory cartridge change when the “cartridge” was “empty’. We found out however that the printers will go on a non-recoverable error after they hit their hardcoded print limit, at that time we did not know why and we needed to replace the motherboards (out of warranty, of course) the EPSON scam was revealed some years later. Apparently they did this because they calculated that after X cleaning cycles, the absorbent material inside the printer will be soaked and they wanted to avoid leaks and lawsuits. Lawyers. Go figure.

      1. Were you producing those machines that take photographs from various sources and print them onto big flat rectangular cakes? Nifty. I bet the icing recipe was critical.

        For the printing limit I might’ve tried looking on the PCB for a little 8-pin serial EEPROM, and reading it between prints.

  2. “Gum arabic” – boy does that bring back some memories.

    Ahem. I once made my own photographic paper by dissolving gum arabic in a hot water/metho mix, and then, in darkness, mix in and dissolve silver nitrate crystals.

    Next, in darkness, paint the mixture onto some heavy paper and leave it to dry – in darkness. Helps to use a heavy weight to keep it flat.

    Next, find a photographic negative (or a stencil), affix it to a sheet of the photo paper, take it outside, expose it to sunlight for a few seconds, and process in a weak photopaper-developer solution, stop and fix. I got something resembling the style of a Henry Fox-Talbot image.

    I’m pretty sure that particular experiment convinced the interviewers at photography school to let me in.

    The connection to gum arabic came after some research – pre-internet!! Painting a gum-arabic-free mixture straight onto paper gave poor results as the mix was absorbed by the paper and the image seemed to bleed, probably because of the nature of the fibres in the paper. Using gum arabic somehow kept the photo-sensitive stuff off the paper and within the “emulsion”. Anyway, I’m glad to see gum arabic still useful.

    1. Interesting story – thanks for sharing!

      Always aimed to try something like that, but the furthest I got was coating a piece of paper with a black wax crayon in primary school, and putting in the back of a Brownie box camera. Set the shutter open for a day aimed straight up. Got a black line on the other side of the paper, tracing the path of the sun through the sky where the wax had melted through. At least nothing caught fire.

      Then realised that solid colours on newspaper faded over many weeks’ time in sunlight, so put a piece in the Brownie, aimed it at some building, and waited. Was never patient enough to see an image though because I kept opening the Brownie to see if the newspaper had faded to show a “photo” of the building.

  3. I never knew anything but HP ThinkJet printers used ThinkJet ink cartridges. The original ThinkJet ink only worked properly with special ThinkJet paper. Then HP introduced ink cartridges for plain paper in black ink. There were also red, green, and blue ink cartridges. IIRC those were for transparencies. Dunno if they had to be special ThinkJet type.

    What I’d like to see done is to do an RGB image separation then layer all onto a transparency in a ThinkJet and see how it works on an overhead projector.

    1. I ‘member when the first “plain paper” inkjets were out, but you could still see a bit of fuzziness and bleed on “normal” paper. Then some while later the paper came to be “all purpose” so I’m never sure if the paper changed as much as the ink did. Meaning if you dug up some ’80s copy paper or typing paper whether it would bleed a little on modern inkjets.

  4. Wow, I never thought I would see another Diconix printer as long as I lived! I had the wide-carriage version of that same printer way back in the 90’s, and I was ahead of the technology curve back then in the days of 9-pin dot matrix printers. Eventually it became impossible for me to source the replacement cartridges (internet commerce wasn’t really a thing yet), and I replaced the trusty old Diconix with a series of cheap, off-the-shelf, sold for less than the price of an ink cartridge color ink jet printers, until I finally wised up and just switched to a decent HP laser printer.
    That brings back some memories, like having the quietest and sharpest printer around, being that one weird guy with the wide-carriage printer, and searching high and low for a place that could sell me a vastly overpriced ink cartridge or 3. I don’t miss the old Diconix, but it was unusual even back then, and I literally haven’t seen one in over 20 years.

  5. OK if I go off on a tangent? Tough, I’m gonna anyway.

    You know how modern inkjets put little yellow dots on documents to ID the printer that printed them? It’s to help spies, spooks, governments, police identify people. Personally I think unless you’re printing ransom notes, it’s nobody’s business what you print.

    Anyway… How about crossing a couple of wires so that magenta and yellow are swapped? So you’d be able to see magenta spots much easier than yellow ones. And then, for your images, use a graphics program to swap round the magenta and yellow channels, easy to do. Or even hack a printer driver, if that’s possible. Maybe even a shim, a driver that reads in “print to file” prints, swaps the colours, then spits them back out to the normal printer driver. Or another file, either.

    I’m sure in Linux this is just 1 line in a config file. But the file is one of 2,800 similar terse and incomprehensibly named text files, some of which are obsolete and some only used in some circumstances, which you’re expected to know even though nobody will tell you, and even the person who implemented that has forgotten about it by now.

    But you see my point? You’d need a physical shim for the print head with a PCB in it to swap the contacts around and a bit of 3D printing to hold it together. Then any way you like of swapping round the colours.

    Then you get out your purple marker and gently colour in the dots.

    Sneaky bastards. One more example of people not actually “owning” the things they pay for. If you own something, it obeys your wishes.

    Except cats.

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