Potters & Sculptors - Making Rock from Mud
Bottom-Left: is Clear Blue Mistake.
Bottom-Right: Minspar has been replaced with Wollastonite leading the glaze to become opaque and start to crawl from too much magnesium.
Top-Right: Brian Kemp Lichen with even more magnesium is crawling over a stiff glaze with a low Silica-Alumina Ratio. Make the bottom glaze runny and the two glazes melt into each other and mix - and usually not in a pretty way.
Top-Left: This 'celadon' glaze could be quite beautiful applied like the Lichen glaze over another glaze that is stiffer, less runny with low magnesium levels.
Some people accidentally make this problem worse by using Epson Salts to flocculate their glazes, adding even more magnesium, rather than something like calcium chloride.