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Amaco stoneware - blue glaze turned out to green


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Hi,

I’ve applied PC023 Indigo Float, PC021 Artic Blue, PC027 - TOURMALINE and Frosted Turquoise (PC-28) on 4 cups as seen in the picture. The cups were fired at 950 Celcius and and second fire was 1250 Celcius. How it is possible to deep blue glazes turned to all green after glaze firing? Do you have any experience with that?

https://ibb.co/L83fPCC
https://ibb.co/59nv60v
https://ibb.co/bWbPJcz
https://ibb.co/yYhwmB1
https://ibb.co/zHfxpfM

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Hi Sedef and welcome to the forum.

Looks like all the glazes you used are recommended to be fired to cone 5/6 which would be approx 1200C tops. It's quite common to the the first (bisque or biscuit) firing to cone 04 (approx 1060C). 

A few things that can have an effect on how a glaze colour turns out. Claybody the glaze is used on, most commercial glazes are tested on buff or light coloured clays, darker clays will have a different look to the colour of the glaze. Glaze thickness and temperature / cone fired at are also factors. 

edit: if your clay is a high fire clay then you would either need to use high fire glazes and keep firing the glaze fire how you are, or find a clay that matures at midrange, cone 5/6 for those glazes.

Edited by Min
Temp typo
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Of all those glazes only indigo float looks like it doesn’t have a green tendency in it. The others vary with thickness. Certainly the clay underneath will affect the color. The speed of firing will also affect it, sometimes significantly. Using physical cones will help you know what’s really going on in the kiln. If your kiln is plodding along at 60°C/hour for the final hundred degrees, then 1250°C is cone 8. 

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Thank you so much for your answers. The clay was light creme color. I think I need to check exact Celcius degree that corresponds to the cone value. I thought that 50C (1200 to 1250)  don’t make any significant change but I guess I was wrong😅

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