When I started wood firing some 30 years ago I had a problem with the kiln so I wrote a letter to ask advice from Steve Harrison in The Land of OZ. 6 months later I got an answer, tried that, wrote back, and all told it took about 2 years to get the answer. Then I joined Clayart Discussion group and answers came in the next morning. One of those people on the list was Craig Martell. Steve Harrison was too.  They

and  I aren't there much anymore. I found Craig on FB. He is a man with a solid ceramic brain. I had this wonderful gold lustre come out on porcelain and a rainbow trout effect on my high iron stoneware. I wrote FB to ask how I could get it again so that I might buy a Rolls Royce like Otto had. Kathy in Florida told me I Otto start calling Sheila Vivika.
Here is the brilliant answer of Craig Martell.

Craig Martell The term for this lovely, pleasant phenomenon is: "bi-refringence. It's the same deal as oil slicks and rainbow lustre on chrome tailpipes. The light is reflecting from both the surface and the underside of the glaze and the crossing wave lengths cancel out some of the others and create this effect. I think one factor is to glaze thin along with having the magic recipe. I got this info some years back from Michael Banks a potter and mineralogist from New Zealand. Not a real solid explanation from me but maybe you can do a search on the net and get some real focused info. Beautiful cup dude! I hope you can make more.


June Perry said…
Great effect Tony. You might want to get up to Terra Cotta and get some of that red clay and test it as part of all of your recipe. I saw a photo of the grid Craig did years ago with this effect and believe he said that he had gotten that effect with some local red clay.
smartcat said…
Gorgeous! Looks like you are holding a cloud at sunset.

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