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Pottery/Glaze Cracks and Health Issues



I have some lovely green glazed plates from Portugal and although they feel as smooth as glass, I can see hairline checking.  Could this present a health concern?

Dear Judy,

    Thank you for your recent question. Yes, any glaze that depicts hairline cracks could pose a problem. The first is from bacteria setting into the cracks. Although the cracks may be minute, so is bacteria. The second comes from the glaze itself. Glazes produced overseas do not have the same safety protocol as glazes made in the states. Therefore, you may have a glaze that is made with lead, barium or other toxic materials that may leach from the plates if they were not fired to the maturing temperature, especially through the cracks.

    Since you stated the plates are very smooth, there is a test you can do to see if the glaze is actually cracked completely through to the surface. Using a straight pin, gently but firmly drag the head across the plate, over one of the cracks. If while holding the plate close to your ear you hear the pin head catch or skip over the crack, then the plate will catch bacteria. If the pin slides smoothly over the surface, then the glaze was most likely coated with a clear over glaze and will be safe to use.

    As for leaching, you may wish to purchase a leach test to test the glaze surface of the plates to make sure there are no glaze materials leaching from the plates. In my opinion, I would not use the plates until these tests are performed, for your safety.

    You can purchase a leach test at any hardware store and it is good for many tests on various pottery items you may purchase or wish to use.

    I hope this answers your question. If you have further questions, please feel free to contact me again any time. Always at your service.

Ms Ti Phillips
Earth Stoke 'N Fire Pottery Studio and Artist Retreat


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Ti Phillips


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 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.

Alliance of Pottery Artists Worldwide Association

Ceramic Industry - PPP Wyndstryder Press - Pottery Journal

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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