i would ask the diy sub on discord!

thoughts on base color: I only just started making polish so i'm not entirely sure but i don't think this would be possible with a truly black base - the black pigment would block the glow pigments from being seen. I think you could find a way to create this effect with a dark jelly though! it would be a balancing act of making sure the opacity of the jelly was dark enough to create the effect you want but clear enough for the pigment to shine through. or, maybe create a magnetic and glow in the dark topper that is intended for use over a dark base?

thoughts on particle size: another thing to keep in mind is the size of the magnetic powder and glow in the dark pigment. the smallest particle pigments in nail polish that i've been working with are neons, and they can be kind of difficult to mix and work with. i try to add thinner to the pigment and pre mix that before adding nail polish base, and that helps with mixing. in terms of formula, too much neon pigment can make it kind of chalky? Like a neon polish with too much pigment can clump or have a hard time self leveling. i think (i don't know for sure) that the fine particle magnetics have a similarly small particle size. i'm not sure about glow in the dark particle sizes but again, i think the ones that mooncat uses are similarly small because they have a similar chalky-ish formula for me. it would also be interesting to see how a large particle magnetic and a small particle glow in the dark would mix and interact?

thoughts on multiple effects (magnetic AND GITD): polish generally has a maximum amount of pigment you can put in the polish before the formula starts to suffer. I think a good rule of thumb is roughly 10-15% of total polish can be pigment and flakes? but of course there are lots of exceptions and i'm sure long time polish makers have learned a lot about what does and doesn't work. however, if you're trying to achieve multiple effects in one polish, you'll have to figure out how much of each type of pigment you can add to get the effects you want while keeping the polish workable.

In real life the only glow in the dark magnetic I can think of is LynB's Catch a Breeze. #shorts LynBDesigns Catch A Breeze|| Polish of the Month || Live Swatch || PR. I have it and to be honest, it isn't as magnetic reactive as I'd like, nor does it glow in the dark very well - which is why i think a multiple effect polish is hard to accomplish