Expert: Leisha Hiester - 9/8/2008

Question
I summited this on Sept. 3 to another person and have not received an answer as of yet.  I am trying again and looking forward to hearing from you soon.

"I want to make clay tiles to use as warmers in bread baskets.  What type of clay do you recommend, what are the tricks to keep the tiles from warping when fired and will they still work for warming bread if glazed?  Also, do you know what temperature to warm the tile in the oven and for how long when using as a bread warmer?  I also would like to try some tile projects with children.  Any advice for no fail projects?  I seem to have problems keeping stoneware fired to cone 5 to stay flat.  I know I have asked several questions and will sincerely appreciate your answers so that I can pass the love for clay on to several hundred children."


Answer
Mary,
I'm sorry you didn't hear back. I'm also sorry for my delay. I've been battling a tough cold. Please remember all the experts are volunteers.

That's great that you're making bread warmers! The key is to get the clay 'vitreous' which means it is fired to full maturity. Vitrification is the point at which clay particles fuse together. In other words, if you're firing a mid-range clay, cone 5-7, you want a clay that matures at a specific cone, not a range clay. If your clay matures at cone 6, fire to cone 6. If you're high firing & a clay matures at cone 10, make sure you fire to cone 10.

As far as warping is concerned, clay has a memory. So if a tile or flat piece is bent during construction, then when the heat is applied in firing it will remember that bend & go back to it. When drying flat pieces dry them in between boards. I use pieces of drywall in my studio. They work perfectly & draw moisture out at a perfect rate.

It may be difficult when working with kids to ensure the pieces aren't bent around during construction. One sure way is to fire the pieces between kiln shelves. I use old pieces of broken kiln shelves in my studio for this purpose. You can only do this, of course during the bisque firing.

I hope this helps. Please feel free to write again if I haven't been exactly clear.

Leisha