Nick Taylor Apr 25, 2013:

I actually use this technique... on my underglazed cobalt blue porcelain fired at around 1100º c intentionally to create the "blurred" edge however I have not yet defined a nomenclature for the effect, I generally refer to it as "bleeding" as the migration of pigment (cobalt blue) infuses into the micro porous structure of the biscuit fired porcelain. If there are any other potters out there who have given this a name I would love to know :-)