Hi PSCO
In addition to Joe's correct assignment of finer meshes needed for some waterbased ink formulas,
there is an additive thickening agent that can be used with many screen inks and paint coatings known as a "fumed silicate":
Cab-o-Sil Filler. M5 Cabosil-untreated fumed submicron silica used as an inert filler to thicken thin liquid systems (polyester, urethane, epoxy, dyes and paints. Available in small quantity. EP7965
Trade names of Cabosil* and Airosil are common,
and companies like Rutland sell it as Thickener #10 (MO-0010).
Note it also works with non-plastisol inks, too.
A little goes a very long way, and if mixed properly, it can do wonders in viscosity increase.
Major handling consideration:
Wear a mask to avoid breathing this "feather-light powder" additive and avoid mixing it amidst high air circulation.
(*Not to be confused with Cabo Wabo.)
Happy trails!