I'm trying to design a digital clock that will use several electromagnets and iron filings to show the time. Each digit should have 7 electromagnets that turned on and off to attract the metal shavings through white plexiglass (I'm also considering using immersion oil to make it easier for the filings to reform). However, I'm stuck on how to design the electromagnet itself. I initially started with a solenoid, however, I quickly learned that the shavings will mainly attract two ends, leaving the middle of the digit line with no definition.
I'm looking for advice on how this might be done. Will wrapping the wire vertically instead of horizontally be a better choice? Should I use a different shape altogether?