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Pottery/Tinging and Popping Pottery

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Question
Hi I am wondering if you could answer this for me.
After we unload our kiln, for a few days we hear the glaze
Tinking/popping. What is causing this?
       Thanks kristi

Answer
Dear Kristi,

    Thank you for your recent question. In most cases, the tinging and popping sounds often occur right after a kiln is opened, especially if the kiln is still warm. This is why a kiln should not be unloaded while the kiln is still warm, but should be unloaded after the kiln cools completely. However, if you are hearing the sounds after the ware is completely cooled, then this represents a stress issue between the clay and glaze.

    Examine the glaze for any defects, such as crackling which may sometimes only be seen when looking under bright light or using a magnifying glass. Crackling will often be uniform and very tiny. This is usually not a problem, even for functional ware. But if the crackle is uneven and large, the glaze does not fit the clay body and will create bacterial issues if the ware is a functional piece.

    Fit represents the thermal expansion of the clay and glaze together. During firing, the glaze spreads over the surface of the clay body, stretching or expanding. During the cool down phase, the glaze adheres to the clay body and begins to shrink back, creating a tight fit on the clay surface. If the glaze has a higher shrinkage rate than the clay body, then the glaze will begin to crack as it cools, creating crackling over the surface.

    In most cases, this is not a problem, as discussed above. However, if the glaze is crackling enough to cause some of the glaze to pop off the surface of the clay body, then the ware becomes unsafe to use as functional ware. Large crackling, where the glaze splits enough where you are able to see the clay body between the crack is also a problem.

    My suggestion to you is to examine the surface of the glaze with a magnifying glass and under a bright light. If there are large separations between the cracked areas or if some of the glaze has actually popped off the clay body, then render the piece as non-functional by drilling a hole into the bottom of the piece. Also, if this is the case, check with your supplier on selecting a glaze with the same fit as your clay body. If you are developing your glazes in the studio, you will need to perform a shrinkage test on the clay and glaze to determine if they are of the same rate. A glaze can be adjusted to match the shrinkage rate of a clay body by the adding additional raw materials, but in order to give you an exact recipe change, I would need to know the ingredients and percentages of the glaze, as well as the shrinkage rate of the clay body. If you need help in that area, then please contact me again, and I will assist you.

    I hope this answers your question and gives you more insight on the problem. If you have further questions or would like assistance in adjusting your glaze, please respond to this topic as a follow-up. Good luck with your ware. I am always at your service.

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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