|Monthly Tech-Tip |
This is G3948A, an iron red cone 6 glaze. The reason for the variegated surface is the high fluidity of the melt. Adequate thickness is also important, enabling it to run downward to some extent. That means this is not actually over fired. Using it thus requires consideration of the running behavior, accommodating it in the shape of the ware on which it is used. Obviously, using this on the insides of pieces would result in pooling at the base, that would likely produce glaze compression, cracking the piece during cooling.
This iron red cone 6 glaze, G3948A, is applied thickly and runs during firing. With no countermeasures, it ends up on the kiln shelf (like the one on the left). Since this glaze breaks-to-black where thin on the edges of contours, glazing the base black seems like a natural match. The base of this was first dipped in G3914A black, up to about 1 cm (1/2 in). I then waxed over all of the black up to within 1-2mm of its edge. Then I applied the iron red by dipping in the normal way for liner glazing mugs. For this thickness of the brown the black melt is able to catch and stop it within 5mm or less.
Ceramic glazes melt and flow according to their chemistry, particle size and mineralogy. Observing and measuring the nature and amount of flow is important in understanding them.