Essentially the paint will not coat the burn where it cuts. Thicker paint?
I’d use opaque colored acrylic.
You can engrave something fun on them.
This is the way.
I completely agree. If they are colored acrylic you don’t need to paint them and you could include a cool engrave on them also!
… but you can. You can fill the engraved sections with a contrasting paint if you want to.
Colored acrylic is the right material for the job.
… or engrave on two-color acrylic and have contrasting colors without painting.
Sandpaper! If you have a belt sander and you hold the pieces 30-degrees from straight they will roll evenly and sand in the process, would be very quick.
Even if you sand off the char, the edges on both plywood and mdf are a pain to paint. The edges just suck it in. I’ve done it, but I’ve never been happy about it.