The particles are aluminium. That isn’t ferromagnetic, but its conductivity is good, so you can induce eddy currents in the particles.
That hints at a totally impractical way to do that with regular etch a sketch: put a strong magnet on top of the screen wherever you want the image to be retained and flip over the device.
Where you put magnets, eddy currents will be induced into the aluminium dust. Those will generate a magnetic field that slows down the particles, as they drop towards the screen.
So, if wait just long enough, and flip the device back, you can prevent those particles from reaching the screen.
Problems/challenges:
- “just long enough” will be very tricky to accomplish
- you probably will need very strong magnets
- it will be a challenge to have well-defined regions where your magnet(s) don’t affect the screen
Thanks for that wonderful exploration of the problem space.
Side note on magnets: when our kids were young, I got one of theose stick-and-ball magnetic sets that are capable of making geometric figures. So I made a Archimedian-style polyhedron big enough to be a helmet. I wore it for some minutes on a few occasions and it gave me a very unpleasant (but subtle) headache and a deep, somewhat lasting nausea.
I try not to put magnets near my body anymore, nor allow the kids to. My understanding is that our bodies were evolved over millennia without being near magnets (or electric fields), especially the neodynium sorts.
Anyhow, thanks for the thoughtful reply. It's the best of the internet's potential.
That hints at a totally impractical way to do that with regular etch a sketch: put a strong magnet on top of the screen wherever you want the image to be retained and flip over the device.
Where you put magnets, eddy currents will be induced into the aluminium dust. Those will generate a magnetic field that slows down the particles, as they drop towards the screen.
So, if wait just long enough, and flip the device back, you can prevent those particles from reaching the screen.
Problems/challenges:
- “just long enough” will be very tricky to accomplish
- you probably will need very strong magnets
- it will be a challenge to have well-defined regions where your magnet(s) don’t affect the screen
⇒ I guess it may be easier (not easy) to cool your etch a sketch to -196 °C and use a strong magnet (https://youtu.be/zU3niMdjegQ?feature=shared)
Easiest probably would be https://hackaday.com/2024/03/27/sort-of-electromagnet-attrac... (likely still impractical for the distance needed in an etch a sketch)