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Pottery/Food Safety at Cone 05


QUESTION: If I fire a clay body to cone 05, and use cone 05 glazes on it, can I use it for food (cookie tray)?
Is it possible to cover the cone 05 glazes with a cone 5 clear glaze and then fire to cone 05?

ANSWER: Dear Rowena,

    Thank you for your recent question. When it comes to food safety and glazes, the question is not how hot the temperature or how high the cone, but whether the glaze is food safe to begin with. You did not specify if you are using commercial or studio glazes, so I will explain the difference and give you enough information to make a determination on whether your glaze is safe to use as functional ware.

    Before I begin, let me state that if your cone 05 glaze is determined food safe, then you can use it on the cone 05 clay body and when fired to maturing temperature, will render the cookie tray safe to use for food.

    It is impossible to use cone 5 glazes on a cone 05 clay body as a cone 5 glaze must be fired between 2150 and 2230 degrees F, depending on the cone size you use. The clay body matures at a much lower temperature, between 1800 and 1944 degrees F, and if fired to the cone 5 maturing temperature, would melt in the kiln. To help you remember, never put a hotter cone glaze on a lower cone clay body.

    Now to determine if your glaze is safe to use. If you are using a commercial glaze, check the label. The label will state that the glaze is safe to use on food ware or it is food safe. However, if you are using studio glazes, those you mix yourself, then you must check the components of the glaze to determine if it is safe to use. Glazes are composed of many different raw materials, each having their own safety issues. But what you are looking for are any raw materials that may leach into food after it is fired, and those glaze materials which are toxic to the body. To make it somewhat simple, lead, barium carbonate, potassium dichromate and potassium bichromate are raw materials that should never be used in glaze bodies that will be used with food. This does not list all materials as there are literally hundreds of raw materials available for glazes, however, you can look up each material listed in your glaze recipe to check for leaching possibilities at the following address:

    You can also send me a list of the ingredients in your glaze and I will be happy to let you know if you have an raw materials that have the capability to leach once fired.

    I hope this helps you. If you have further questions, or would like me to look over the glaze materials, please feel free to contact me at any time. I am always at your service. Much luck to you.

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

---------- FOLLOW-UP ----------

QUESTION: Your answer to my question about food safety at cone 05 was excellent!  Thank you so much!

I have another question, too! This is about glazes running down on pots and going on to the kiln shelf. I make the students clean the underside of their pots, but i am always worried that they may have put too much glaze on the pot at the bottom and that the glaze will run off onto the shelf. Thus I put each pot (they are about a foot high) on stilts. Though they don't feel wobbly when I touch them, is there a chance that they can move in the kiln and somehow tip? I seem to remember that once or twice a glazed object had fallen over in the kiln during the glaze firing. I have a kiln ready to go for a glaze firing full of these pots, but thought I would wait to hear your answer lest I risk a lot of work!

Many many thanks again! Truly appreciate your answers!

Dear Rowena,

Thank you for your follow up question and your rating for your first question. I am glad I can help you. As for runny glaze, to prevent running onto the kiln shelf, have your students wipe away at least 1/4 inch of the glaze from the very bottom edge of the pottery. This will prevent most runny glazes from running onto the shelves.

Stilts are excellent for maintaining height for pottery that may have glazes that run. Yes, they can fall over if the kiln is bumped or the stilts are not placed in a good position under the pot. However, you can check the stability of the stilts you are using under each pot by checking them outside the kiln first. For large pieces, I recommend three star stilts under the pot, positioned at 12, 4 and 8, if you divide the pot bottom into 12 clock counted sections. Place the stilts as close to the outer edge of the pot as possible, then check to make sure it doesn't wobble. This positioning of the stilts rarely causes wobbling.

Finally, make sure you have plenty of kiln wash on each shelf. There should be at least three heavy coats on each shelf to protect it from dripping glazes.

I hope this answers your question. Please let me know if I can be of further service to you. Always at your service. Much luck to you and your students.

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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