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Pottery/Glaze Changing Over Time

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Question
We've been using a Cone 6 glaze for years at our studio, I am on the glaze committee so I've been making this glaze all along. The characteristics of the glaze have drastically changed in the past couple of years.  Originally, the glaze we call Runny Honey, was extremely glossy and ran easily. We always recommend to our students to use it carefully.  It still causes other glazes to move when used over them.  On it's own it was opalescent, quite beautiful - really a wonderful glaze.  Now we're finding that it has become satin to matt when used on it's own.  I will include the recipe for you to examine.  We are getting our supplies from the same supplier, though I suspect something had changed!

Gerstley Borate   14   700   1400
Spodumene   30   1500   3000
EPK Kaolin   5   250   500
Dolomite   7   350   700
Talc   13   650   1300
Flint   20   1000   2000
Rutile   6   300   600
Bentonite   2   100   200

Can you suggest things to try to alter these undesired results?

Answer
Dear Jane,

    Thank you for your recent question. It is quite possible that one or more ingredients have changed the chemical composition over time. As you probably know, with exception to man made materials, all raw materials are extruded from mining sources that can change composition just by moving from the mining source a few feet. I do know that Gerstley Borate is one that has changed composition over the years, and if you have been using the same source up until the change then this could be one area where the undesired effects have taken place.

    Please give me a few days to research each ingredient for possible composition changes and to work an adjusted solution for you. At this point, I am unable to ell you exactly what has caused this problem, but I do have access to many resources that will assist me in finding a solution for you. I hope you have a few days to wait on this and know that I will work diligently on a solution for you.

    Thank you.

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

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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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