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Pottery/Glaze Becomes Sticky When Heated on Mug


I have a glazed coffee mug.
When I use it for coffee it gets a sticky sweet film on the outside of it.
What is this?
Is it harmful?

Dear Donna,

Thank you for your recent question. It is impossible to determine exactly what the sticky film is on the outside of the mug and if it is harmful without more information. Therefore, in order to assist you, I will need you to answer a few follow up questions.

1. Where did you get the mug from? Did you make or purchase it?
2. If you purchased it, is it a foreign cup, say from China or the Philippines?
3. What do you put in your coffee when you drink it, cream, sugar, etc.
4. Is the bottom of the mug glazed? If not, is the bottom smooth or porous?
5. Do you get the same results when you place other hot beverages into the mug? How about when you place cold beverages in?
6. If the bottom of the mug is not glazed, does it too have the same issue of stickiness?

I look forward to your reply,

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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