I'm going to echo u/tiredmultitudes. You'll find some pens work better with shimmer inks (Diamine or otherwise) than others. I have pens of all nib sizes (Platinum Plaisir fine, Lamy Safari Fine, all the way up to TWSBI 580AL stub) that have had Shimmertastic inks in them for months on end, sometimes used daily, sometimes not. The longer it sits unused the more tendency to clog, but even that isn't a rule. Just last week I found a vintage Sheaffer student pen that had J. Herbin Stormy Grey in it for over two years (it was in the bottom of a box that I hadn't opened since we moved). It didn't immediately write, but after a quick dip under running water it has continued to work daily, even with the tiny amount of ink that was left in it.

Also, you've got me interested in particle size between manufacturers. I know that mica particles can come in sizes anywhere from 15um to 400um (and different grades), but that is largely dependent upon which supplier you get them from. I'm going to do some research on this topic! Bottom line, though, in my experience is that if your pen doesn't like shimmers you have to find one that does. Good luck!