If my mesh is too fine I get stuff that does not pass through it but obviously needs to be in the glaze. How do you get those into the glaze? Am I not mixing it enough first?
Also, I think glazes improve if the raw ingredients are fine milled before ... I don't think the screen mills them any finer just breaks up clumps??
Run the power mixer longer to break up as many clumps as possible before sieving.
Most glaze materials are 200 mesh or finer, however that's not always 100% accurate, and some materials clump up in to quite hard chunks that can be difficult to break up with the screen. You should technically be able to run a glaze through a 180 mesh screen, although it will take a long time to work it through a screen that is that close to the particle size of the materials. I think anything over 100 mesh is overkill for most applications, or if it won't go through your sprayer. The only time I've seen anything finer required was using a particular stain that would clump enough to cause speckles in the glaze rather than being perfectly dispersed in the glaze. In that case, the stain was sieved through a 180 with a small portion of the glaze batch. There was no reason to sieve the entire batch that finely, since only the stain was the problem.
A ball mil will actually reduce the particle size, although for most glazes it's overkill. Not worth the effort most of the time. Many glaze manufacturers us high shear mixers for their glazes, which negates the need for sieving and can also reduce the particle size.
If you're not having any problems with the 80 mesh, no need to do anything finer. The small the mesh size, the longer it will take to sieve the glaze.