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Hi all,

Happy New Year to everyone!

I'm interested in firing stoneware dishes without using a glaze. I only want to use coloured slips. Would this still be food safe? I spoke to a potter at a rather prestigious  ceramics event in London and she didn't use any glazes. I asked her if her ware was foodsafe and she told me, yes. I'm guessing that the high-fire temperatures will vitrify the clay sufficiently to make it washable/hygienic/easy-to-clean? One of the reasons I want to do this is so I can stack the shallow dishes on top of each other during the firing - but I also like matt finishes. I know there are matt glazes available but if I can skip this part, it would make my life a bit easier...and cheaper! 

Thank you in advance :)

Edited by Momo
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Hi Momo!

I'm curious to see how the community will answer. I stack for bisque fire, however, not sure how pieces - the parts touching - will do in glaze fire; my guess is there could be some sticking.

Any road, as far as food safe, even the very low absorption (less than 1%) stoneware will stain some, which is ok for some users. That said, I'm glazing all food surfaces for any pieces that will be in other's hands, and I'm committed to clear, glossy, un-crazed and long wearing liner glazes.

Other considerations: a) that glaze strengthens pieces is well established, b) "food safe" - technically, no lead or cadmium? - isn't nearly strict enough, my opinion

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Your trick will be finding a clay body that meets your requirements.  Did the potter at the event make kitchenware?  I don't glaze the inside of my pots and will merrily stack as much as I can fit.  I usually use some kind of spacer between the pots.  Little slabs of soft brick mostly, sometimes alumina.  Generally stoneware won't stick and porcelain will.  I have a pizza stone that is what I would call oven ware.  It's quite stained from food.  You'd be looking at a really fine grained stoneware.  There will be troubles on this path, I think.   

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3 hours ago, Momo said:

Would this still be food safe?

Depends on what your definition of food safe is.

Load up the slips with colouring oxides or stains and hope they don't leach? Create a tight non porous surface that doesn't absorb oils and moisture? 

3 hours ago, Momo said:

I'm guessing that the high-fire temperatures will vitrify the clay sufficiently to make it washable/hygienic/easy-to-clean?

Not necessarily. There are plenty of high fire stoneware bodies out there that have absorption in the 3 or 4%. Equally there are midfire claybodies that do vitrify enough to have very low absorption. 

How does cutlery sound being used on it and does it leave marking on the slip? Drag a knife or spoon across the bottom of an unglazed pot, it's going to sound scratchy and unpleasant.

3 hours ago, Momo said:

I spoke to a potter at a rather prestigious  ceramics event in London and she didn't use any glazes. I asked her if her ware was foodsafe and she told me, yes.

With all due respect this doesn't really mean anything. If there is nothing nasty to leach out of the slip and it's vitrified then will it harm anyone? Probably not. Is it a good idea for functional ware? That's up to you to decide but I wouldn't do it.

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I wouldn't rust a colored slip to be food safe/non leaching. I just wouldn't trust a clay body to go into melt enough to truly lock up any metals. Has the person you spoke with actually sent her work off to a lab to be tested? You would need to test every recipe you use.

Raw clay is going to stain with use. It's going to wreak havoc on metal and wood utensils and cleaning tools like sponges and scrub brushes. It's going to sound and feel awful every time a utensil touches it. Restaurants are required to use vitrified, glazed ware for hygiene reasons.

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cactus pots, i use pizza stones in my little test kiln as shelves.  the kiln only takes 12 inch shelves so i tried one and it was fine, totally flat after a cone 6 firing.   l found a larger one at a thrift shop and when i used it, it warped unbelievably.   different material,  different results.  it was also fired in my larger kiln but to cone 6. 

the best part was that my original pizza stone was very dirty so i put it into a cone 06 firing to clean it and it came out like new.   that is when i realized i had something more than just a pizza stone and moved it permanently to the studio.

Edited by oldlady
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