January 18, 2011 - 8:49pm
A word of caution regarding kiln shelves
As a baker and a ceramist I thought I would put some information regarding the use of kiln shelves for baking bread. I don't know what the effect of using a NEW kiln shelf for baking would be but I do know that kiln shelves that have been used to fire ceramics are most often treated with kiln wash to prevent glazes from sticking to the shelves. The kiln wash is made of silica sand, alumina hydrate and kaolin and this is NOT a food safe material. Usually the underside of the kiln shelf is not treated with this so it may be possible to use the untreated side of a kiln shelf, but once fired the kiln wash is impossible to remove and caution should be taken so that it does not come in contact with food.
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What home bakers really want is the material "cordierite"; it's typically used in "brick ovens" like your local pizza parlor probably has. But that material tends to not be easily available to the general public in smallish quantities (anybody have an oven 80 x 120 inches?-). Fortunately though that material is often available from pottery supplies as a "kiln shelf".
Because not every noob understands right away that what really matters is the material "cordierite", and the association with potters is largely irrelevant, your warning is quite prudent. (Fortunately there doesn't seem to be much of a market in "used" kiln shelves, so home bakers don't have much chance to poison themselves that particular way.)
I live in UK, so the situation may be different in US, but a cordierite kiln shelf is quite easily available, in small quantity, too, from a kiln manufacturer here in UK, if anybody is interested. I searched for a kiln equipment wholesaler/manufacturer in my local area on internet, phoned them and they were quite happy to cut it for my to fit my oven. They assured me it's completely food safe and the only possible health hazard is dropping it on your foot! :p
I was referring to USED kiln shelves that may have been coated with kiln wash. While used shelves may be in short supply I just wanted to inform those that may come across one and want to use it for baking. Many of the older glazes contain lead and that is another reason to stay away from used shelves as there may be traces of this embedded in the kiln wash.