Ceramic glaze application & technical defects: the tv effect

Speaking of ceramic glaze applications and technical defects, one of the strangest and most interesting is the "TV effect".It consists of a preferential migration of the glaze towards the perimeters of the tile that produces in those areas a thickening of the glaze.The unaesthetic result is a quite regular surface swelling along the edge of the ceramic material. A result that recalls the old cathode-ray television sets and that may be visible even after the firing cycle.What is exactly the TV effect? How does it manifest itself and what are the causes?What can we finally do to prevent the problem?