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Pottery/Clay/Glaze Fit?

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In December I made some coffee cups with a brown clay and Coyote glaze which I purchased in liquid form. When I opened the kiln I could hear them pinging faintly.  I filled them with water and placed them on a paper towel and in about 15 hours they finally wicked through.  But that glaze has been so reliable for me on other clays so I tried it again on a different brown clay thinking its a fit issue.  On this piece there was no pinging or wicking after 24 hours. I thought I was in the clear, so I ordered additional quantities of the glaze in dry form.  On my test piece (using the second clay and glaze mixed from dry) I have heard no pinging but am starting to notice slight dampness on the paper towel after 12 hours.

Is there a way to solve this wicking issue? On my current fired test piece and/or future pieces?

Answer
Dear Debbie,

    Thank your recent question. The problem with your ware wicking is either due to the fusion of the raw materials in the new clay bodies or the thickness of your glaze application. Let's begin with the glaze application first.

    When you purchase a glaze that is in liquid form, the glaze will not have a true suspension. This will be due to extra water added to the glaze by the manufacturer so that the glaze doesn't dry out before being sold, or the lack of water due to evaporation. Before using a glaze, you should the viscosity using a hydrometer. Many of the manufacturers will tell you what the viscosity number is for the glaze you are using. This will allow you to adjust the water content of the glaze so the application will be consistent from one application to another. Once you have the correct viscosity the apply the glaze with at least three coats, as usual.

    The second reason you may be having this problem is due to the change in clay bodies. Just as each glaze has a particular composition, so do clay bodies. And each clay and glaze fusion will be different as you change a clay or glaze. In your situation, you changed clay bodies and the fusion changed during firing as well. When the raw materials from the glaze fused with the raw materials from the clay body, there was probably a different interaction that caused a weaker fusion. This could also result in a change in fit, causing the pinging in the kiln and later the wicking.

    Since there is no way to tell which way the glaze is moving, either expanding or contracting during the cooling enough to cause the problem, there is really no way to give you a correct answer for fixing the expansion or contraction problem. I suggest that you return to your original clay body to correct the problem since you are making functional ware. It is extremely important that the glaze fits the clay body when making functional ware.

    I hope this answers your question. If you have additional questions, please feel free to contact me at any time. I am always at your service. Good luck to 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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