Da blues (1)

Looking for a new Cone 6 glaze I came across the chapter on Jun Glazes in Michael Bailey's wonderful book Glazes Cone 6. I tried his Jun Base 1 glaze, which gave me a very reliable, soft blue result on a buff stoneware clay (Creaton 359), and an even more subtle violet tint on a French stoneware clay (KPCL Limoges KF 100).

Also, on a clay with iron specks, the results were promising.

But the real possibilities of this base glaze became clear when I tested it (amongst many others) over a high temperature tenmoku. Depending on the thickness of the layers it gave me a bright sky blue, all the way to a violet-brown tint.

And what made it even better: the way it breaks over sharp edges and rims.

Later on I tried it over a commercial black glaze (Keramikos SG840). The blue changes to a midnight blue with black to grey rims.

Every book on glazes will tell you that these wonderful blues are not the result of a pigment in the glaze, like cobalt is a pigment, but "an optical effect, brought about by the scattering of light at the blue end of the spectrum" (Bailey).

In the next blog I'll try to sort out just what that means.