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Pottery/Lowering the Maturing Cone of a Glaze

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Question
Hello Ti. I have read through previous questions and answers as well as some research both on the web and in books and wonder if you could help me with a glaze problem.  I have a glaze that seems to have a wide firing range.  It is actually a cone 6 glaze but I have tested it at lower temps between 1100 degrees celsius and up to approximately 1120 degrees celsius.  It is a good glaze for stamped and carved work and seems good so far for stain responses as well.  I am wondering if I can lower the glaze maturing temperature to cone 05 by adding percentages of Lithium? rather than testing out a whole new batch of low fire glaze recipes.  My kiln is a old Duncan and only fires to 1100 which I have then allowed to soak. Last time I soaked at 1100 degrees for 3 hours and this glaze seemed fine on my test tiles and small bowls.  I would like to fire lower without having to pray to the kiln god for the extra 20 or so degrees!  Having said that, praying is definitely cheaper than buying a kiln!  Here is the recipe:

Potash Feldspar 40
Whiting 15
Zinc 10
Kaolin 15
Silica 20

I can add 2% of stains with good response and would like to experiment with oxides as well.

I have been using a wide range of clay bodies from terracotta and earthenware to mid-fire porcelains and mid-fire stonewares and have found this glaze not to craze on these bodies thus far in my testing.  But, I would like it to 'fit' better. Last firing a discovered a little bit of crawling on a larger pot, coffee cup size.

I also want to say that what you do here on AllExperts is amazing and I am so grateful we have you here to answer our questions.

Answer
Dear Janette,

Thank you for your recent question. My apologies on the timeliness of my answer. I had a hospital stay due to a cat bite and was just recently released.

As for your question, yes, your glaze can be reduced to cone 05, however, I will need to calculate the adjustments to get a true glaze fit and keep the same glaze characteristics for you. Please allow a couple of days for me to calculate the glaze and I will send the new glaze recipe to you via AllExperts.com.

Thank you for your patience.

Sincerely,
Ms Ti Phillips
Earth Stoke 'N Fire Pottery Studio and Artist Retreat
www.earthstokenfire.com

Pottery

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Ti Phillips

Expertise

Will answer any questions on hand building, wheel, glaze, firing. Speciality questions to include those in glaze calculation and development, firing techniques. Please do not send questions on identifying pottery. Although I would love to add this to my question topics, I have a retreat to run as well as the studio and volunteering on AllExperts, and therefore do not have the available time to research indentification and marks. Thank you for understanding.

Experience

Experience includes 30 years in pottery design and education. Have taught online and studio classes worldwide for the last 20 years. Own a pottery retreat specializing in firing techniques. Have 12 years solid experience in glaze calculation and formulation as well as problem solving in glaze chemistry. I am the first potter in the United States to have developed a complete package of pottery equipment blueprints for a studio. The blueprints include wheels, kilns, studio furniture, wedgeboards, raku kilns, slab rollers, ball mills and studio tools.

Organizations
Alliance of Pottery Artists Worldwide Association

Publications
Ceramic Industry - PPP Wyndstryder Press - Pottery Journal

Education/Credentials
University of Sciences and Art's of Oklahoma, studied under Professor Jaymes Dudding.

Awards and Honors
Potter of the year with APAWA, various awards for showmanship and design.

Past/Present Clients
Available upon request.

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