This glaze has just been applied to a bisqued tile. It contains wollastonite, which can agglomerate in storage. The white wollastonite lumps can be broken down by sieving the slurry through 80 mesh or finer. Many other materials behave in a similar manner (e.g. barium carbonate, iron oxide, cobalt oxide, clays, tin oxide, zircon).
Sieves are important in ceramics for removing particulates and agglomerates from glaze, engobe and body slurries.