This cone 6 white opacified glaze has an addition pigment-bearing granular mineral to create speckle (e.g. illmenite, manganese granular, ironstone concretions). This speckling mechanism can be transplanted into almost any glaze. Unfortunately, the metallic particles that produce the speck are often heavy and settle quickly in the glaze slurry. This can be prevented somewhat by flocculating the slurry.
Specking is a fault in fired ceramic ware where speckles of ion bearing contaminants are visible and mar the appearance of the surface.
Stop! Think! Do not get addicted to the trafficking in online glaze recipes. Learn how they work. Understand them. Then make your own or adjust/adapt what you find online.
Identifying the mechanism of a ceramic glaze recipe is the key to moving adjusting it, fixing it, reverse engineering it, even avoiding it!