Chun Recipes, Firing Tips and Scientific Explanations requested:
I was browsing the web yesterday and an article on Chun glaze caught my eye. It said that chun glaze is blue because tiny imperfections bend the light so we see blue. This is the same thing that makes the sky or a bluebird's feathers blue. What a great science project.
But since I have never used a chun glaze, I thought I would ask for some input and some glaze recipes that show this effect. Any tips for firing would also be appreciated. I am linking this post to the cone 5-6 chun recipes that Sylvia Ramachandran gave us years ago. Cone 5 Chun recipes can be found at http://www.websitetoolbox.com/tool/post/clayarts/vpost?id=1263987
Here is my research from last night. Thanks for adding to it.
Steve Sheridan writes, 'Chun' is the name of a classic Chinese glaze that first came to prominence in the Sung dynasty ( around 1000 ad ). It is renowned throughout the world for its flamboyant appearance as a bright blue glaze: technically, it is an unusual type of glaze in that it is not a blue glass at all (unlike celadon, which is a blue or green glass and glaze). The colour in chun is due to reflected light caused by the glaze structure being opalescent; the minute bubbles and phase separation of the glass as it cools gives an opal effect resulting in a vivid blue appearance. The glaze itself when examined through transmitted light is actually yellow.
Artist Ian Dowling notes that the chun glaze alone on pale clay is almost clear. Microscopic bubbles of one glass floating within another glass create true opalescence. Light is refracted (bent) and diffracted (separated into colors) through these phosphorus bubbles. If a dark background is provided, for example, using a temmoku underglaze, a range of blue colours may be reflected while other colors are absorbed.
Ian Dowling believes the intensity of the colour depends on some known and on many unknown factors. The size of the phosphorus glass bubbles and iron particles are important and these are affected by the firing to 1320oC - the time taken at various stages, the degree of reduction (elimination of oxygen), and the cooling phase. The thickness and viscosity of the glazes also play a part.