Elke
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Hello glaze makers!I have a very niche issue and thought someone here maybe able to help me.I was commissioned to make a series of 8 large bespoke ceramic pitchers in a specific colour. They are to be presented as awards at a commemorative event on Dec 10.My customer selected a soft green finish from one of my existing pieces that was glazed in a traditional oribe glaze and fired in oxidation in a wood kiln ( in a group fire in Gunderoo NSW)I have a small Port-o-Kiln and assumed I could replicate the green colour by using the exact glaze (same original batch) and firing to cone 9-10 in oxidation in gas.When I opened the kiln this morning all were BLACK!!I am not sure why. Its either because I didn't go high enough - I found out the group Gunderoo wood fire went to cone 12-13.Or because it Port-O-Kilns cool quickly and when you look up oribe on Wikipedia there is a section that says Black Oribe is achieved with a rapid cool down.Either way I have to urgently refire existing pieces to cone 12-13 or remake all agin which is a ton of work.Does anyone have any understanding of the chemistry behind this?Could I refire to higher temp and the glaze continue to mature and achieve the green colour?Any advice or insight is greatly appreciated.RECIPEPotash Feldspar 60Wood Ash 20Whiting 10Ball clay (clay ceram ) 10Bentonite 1 or 2%Copper carb 7.5
HELP! Green oribe glaze was underfired and came out black - Can I refire to correct temp??
in Clay and Glaze Chemistry
Posted
Thank you thank you everyone!!
After more research I do think it was partly a temperature issue, copper needs high temps to burn out and for the glaze to move and run. I alos used my gas Port-o-kiln which is desigend to rapid cool unlike the wood kiln I had used before.
This batch of glaze had been tested in a kiln run off gas and also waste vegetable oil (a very experimental sustainable kiln), in oxidation , and it came out perfectly transparent, shiny and green.
I definitely did not go into reduction, I have fired this glaze in reduction to cone 10-11 and it goes a marvellous shiny spotty glossy red.
The matt metallic black was a surprise.
MY QUESTION (for those how know a bit about glaze chemistry and heatwork)
Will the metallic black burn off if I refire to cone 12-13 and cool slowly?
I am thin on time, so I want to crowd source some advice to make the smartest move.
I have attached screengrab of the original wood-fired green pot and my misfires black pitchers. Both were lined with Tenmoku.
THANKS!