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Using Low-Fire Slip for Bakeware: Article or Project

I have noticed a lot of debate of late (online) regarding the use of ceramic utility ware. There is a lot of question and misinformation circulating which I would like to help clarify.

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Most often bake ware has been monopolized by potters who use a high fire clay to produce ware which is ideal for baking. This actually dates back to the beginnings of man, who accidentally discovered clay in their fire pits that had hardened to a significant strength and useful for many purposes, especially cooking and serving food.

Clay ware has come a long way with many improvements. It remains true that the high-fire clays are ideal for baking; but it has been proven that low-fire clay bodies can create functional cookware as well with some limitations. Also, with the involvement of the EPA and safety standards it has become a favorite of low-fire ceramists.

So, with simple basic steps, functional bakeware is easy and beautiful and safe to use. Of course these basics require the use of food safe clay and food safe glaze finishes. But more importantly is the original firing process.

ABOUT CASTING

Utility ware should be cast heavier than decorative items. In fact, in many cases, they should be cast solid. If your item is not designed for solid casting, then they should be cast about ¼ inch thick. This is important in order that the ware can hold up to the frequent temperature changes during use. I encourage anyone wanting to cast their ware to visit the Boothe Classroom where you will find several videos on how to cast perfect utility ware. This includes dishes, bowls and of course bakeware. See: http://www.boothemold.com/classroom/default.htm.
You may find it a good idea to let your ware dry upside down as it usually helps prevent warping. In some cases, you might want to lay something on top during the firing process like chalk or wall board, which will add a little weight to prevent ‘curling’.

ABOUT FIRING

When firing your ware, keep in mind that large flat pieces should NEVER be fired on the bottom of a kiln. Where possible, especially during the second firing, try to tilt them with uneven stilts to relieve the pressure on the middle and prevent cracking.

Fire greenware to full maturation to cone 02-03 (see following information)

Fire glazes according to product instructions, keeping in mind to choose items that are food safe.

It is highly suggested that when making cookware, you consider the end user. It is not known if they will be baking in a traditional oven; or, as is very common, use a microwave. All bakeware needs to be fired to cone 03, microwave use to cone 02. Since you don’t know how the ware is to be used, it is suggested to just hold to the cone 02 as routine. Even if you are making it for yourself and you know you won’t put the lower cone items in a microwave, you can’t foresee it going to someone eventually who may.

Thermal shock is why you need to make sure items to be used in the oven or microwave are fired to high maturation in the greenware to bisque state. This makes the ware more durable. Low-fire clays are more sensitive to thermal shock. This is the same principle as avoiding removing items from a hot kiln. High-fire clays and slips are always fired hotter than 02 and that is why they are safer to use. Some/most become so vitreous that they don't even need a glaze because of their glass-like condition after firing. (for another discussion)
When glazing a utility item, be sure to read the glaze labels making sure it is food safe and fire at the recommended temperatures (cones). Low-fire glazes are sufficient.

Anyone using low fire ceramics to bake with also needs to know that the container needs to be room temperature (NOT cold) before putting it into a preheated oven.

If you are selling the ware, it would be a good idea to include a tag/note to indicate that the ware is food safe, useable in the oven and/or microwave (if applicable). You might also want to make note that items should not be taken direct from refrigerator to hot oven. The ware can be taken from refrigerator and placed in a cold oven during the preheat cycle.





 

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Using Low-Fire Slip for Bakeware

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