The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

Baking stone... in London, UK?

  • Pin It
GG's picture
GG

Baking stone... in London, UK?

Hi,


Has anybody based in London, UK managed to find a supplier of baking stones? I am determined not to settle for the pizza stones, but try and find unglazed quarry tiles. They do exists here, just have not managed to find a supplier. 


Much appreciate any pointers.


Best,


Nicolaj


LONDON

Daisy_A's picture
Daisy_A

Hi Nicolaj,


As a UK baker I went round and round the block with this one, trying to find a decently-priced stone the right size for my oven that was food safe, wouldn't tend to crack or explode and which would retain heat well.


Best option I found by far was a kiln shelf from Bath Potters' Supplies. They come in a range of thicknesses and sizes and can be cut to size if required. They are include cordierite, as do better quality baking stones. Prices from just under £11. P n P is extra but the shelf I received was incredibly well wrapped up. In contrast I have heard of similar stones costing £30-£60 pounds from some leading European suppliers arriving chipped or broken. I found customer service to be excellent. They recommend 'seasoning' the stone. Potters would do this with slip. With their advice I did this with flour and water.


http://www.bathpotters.co.uk/category/rectangular-kiln-shelves/221/0-0-0-0-0-0-0-0/1


Hope you find a good option,


Best wishes, Daisy_A

GG's picture
GG

Hi Daisy,


Will have a look at them - looks like the right stuff.


Best,


N

Chuck's picture
Chuck

I am determined not to settle for the pizza stones, but try and find unglazed quarry tiles.


Why?


I've been baking on unglazed quarry tiles for almost two years now. My experience is very definitely they're not better than a "pizza stone".


Even the cost difference and the availability -which used to heavily favor the unglazed quarry tiles- aren't hugely significant any more, as "pizza stones" have become more readily available for a much lower cost while unglazed quarry tiles have retreated from ubiquity to a specialty item.

GG's picture
GG

Trying to avoid 'pizza stones' as they are still relatively expensive (at least in London) and feedback seems to be that they break more easily.


If I could find unglazed quarry tiles at even cheaper prices at a local store, I would have gone for that. But like you say, they have disappeared from the market.


Checked out the kilns mentioned above, and they are cheaper, come in square sizes and can be modified in size at no extra cost. Corcierite also seems to be more resistant to temp differences. Sounds like a good deal to me.


In London, my conclusion so far is that the evolution you describe has not quite happened yet, and the alternatives to 'pizza stones' are still the better opton.


Cheers,


N

Daisy_A's picture
Daisy_A

Hi N,


There is some discussion of kiln shelves and their fitness for baking v. UK available pizza stones, on this thread, from UK baker Zeb. I mention this because she also got her kiln shelf from Bath Potters, so it's a second viewpoint. 


http://www.thefreshloaf.com/node/20289/kiln-shelves


Hope you get something that suits your baking.


Best wishes, Daisy_A

GG's picture
GG

Hi Daisy,


You mentioned you conditioned your kiln. Would you be able to share what you did?


Many thanks,


N

Zeb's picture
Zeb

Hi N and Daisy A,


Just a quick update - my kiln shelf is still all in one piece I didn't condition it, no one suggested it, but at the time I got it Bath Potters seemed a little puzzled that I wanted to use it for bread and were a bit wary about saying it was food safe, but maybe more people have gone that route now.


The pizza stone i started with only lasted a few months and in fact died/cracked all the way through when some tomato passata ran off a pizza onto the stone. Anecdotal but that's what happened.


My shelf is about 3/4 inch thick I think.  I had it cut to leave an inch gap all around, but I think maybe I should have made it smaller, it's a tricky call, too big and the air can't circulate (electric oven). This is a poor photo, but it might give you the general idea. best wishes Zeb


My Kiln shelf and steam tray below

Daisy_A's picture
Daisy_A

Hi N, Hi Zeb,


Zeb I must have come after you at Bath Potters, as they told me they remembered someone else buying a kiln shelf for baking!


I have a friend who is a potter so I looked into the materials, which were cordierite and mullite and cross-referenced them for food safety. Cordierite is deemed to be food safe by agencies such as the US Food and Drug Administration (FDA) and others. Data sheets on mullite state it is relatively non-toxic when ingested, unless ingested in large amounts. Long term exposure to dust is the greater problem with silicates. Obviously this isn't a 100% guarantee as findings change but there are the current findings!


I have a kiln shelf 10X14X3/4 inch. My door seal is gone so it takes a while to heat up at the moment but is a great surface for hearth breads. May get another at 1/2 inch or fix the door seal or both! I lose a lot of heat through poor insulation at the top of the oven so may try using the thinner shelf there. Including pnp Bath Potters had the best prices and most flexible sizes of all the pottery supplies I looked at.


Will gladly share on conditioning.


Conditioning was interesting. Will try to cross-reference to other kiln shelf thread.


I know from talking to potters, including those at Bath Potters, that potters do not use kiln shelves without treating the surface with 'slip' to prevent sticking and staining. This is a loose amalgam of powder in water, which  you apply after brushing down the shelf and before heating it for the first time. 


Talking to Bath Potters we decided flour and water would have the same effect and be food safe. I mixed flour water and a little starter to high hydration - the consistency of cream -  and brushed it on layer by layer, letting each dry, until the stone would not absorb any more. 


However I only did this on one side and potters recommend doing it on both sides as best practice in pottery is to flip the kiln shelf after each use. I have not been doing this in baking but will give it a go, when I have seasoned the other side of the shelf.


I then heated the stone around 3 times, taking it up in increments until bake 3 was around my oven's maximum of 250C.


The 'glaze' does darken the stone, particularly if you do pizza. However it has made my stone resistant to staining and any dough that catches on it accidently is pulled off easily. 


Sealing the stone also makes it less friable so less dust is released during use, which should be healthier in general. 


Information for potters is on the links below:


Kiln wash:


http://jewelrymaking.about.com/od/fusedglassjewelrymaking/ss/makeaglassstudio_5.htm


I have pictures of me doing this with flour, water, starter but can't access them at the moment, unfortunately. As said, I did it with very thin layers, so as not to overload the stone and make it sticky. Consistency was as you see in the picture and I used a soft bristled paint brush.


General advice for kiln shelf care is here:


http://pottery.about.com/od/potterykilns/tp/kilnshelf.htm


Best practice for kiln shelves is also, apparently, to store them on their sides when not in use to minimize stress fractures, as suggested on the link above. I do try to do this with my stone, when I remember. I guess this is harder to do with a round shape. 


As said, rotating the stone after each use is also meant to help prolong its life.


Hope this is helpful. As said I felt very well advised by the woman supplier I talked to at Bath Potters. Don't remember her name, unfortunately, but we came up with the flour, water, starter wash between us, as the best food safe alternative to 'slip'.


I had started thinking about sourdough starter as a thin wash when I made my first starter at 100%, as its lactic smell reminded me of casein paint, which is also put on in lots of very thin layers. I did feel at that time I had enough starter to 'paint my house' let along a kiln stone!


Hope this is of some potential use to other bakers. 


Best wishes, Daisy_A

Zeb's picture
Zeb

It's probably too late for my stone then, it's been baking away twice a week or so since I got it.  But I've only ever used one side, it has a 'good side' and a bad side with a few grooves round the edge where it was cut.  I haven't noticed any dust and the dough never sticks to it, I tend to roll nearly all my breads onto it with fine semolina underneath. But if and when this one dies, I will most definitely try conditioning it too! Most interesting Daisy - wish I'd known this before.  Just had a little trawl through my photos and here is a slightly better pic with 3 x 500 g sourdough loaves squeezed on. I tend to put two on, wait till they have sprung and then sort of shuffle them back and add the last one in...  best wishes Zeb


Kiln shelf in action

Chuck's picture
Chuck

Sealing the stone also makes it less friable so less dust is released during use...


If this turns out to be a good idea, please let us know (I for one am always ready to learn something new:-).


One of the main functions of a baking stone is to absorb moisture out of the crust that's touching it. "Sealing" it seems like it would cancel out this function.


(Cordierite is used extensively in commercial "pizza-style" ovens  ...but the most reasonable way for home bakers to get hold of a piece is through a pottery supply, which knows it as a kiln shelf. That makes me suspect a potter's "best practices" for cordierite are not particularly relevant to using it for cooking. The temperature is very very different. And while "store it on edge" may make sense for a potter, the usual advice for home bakers is "leave it in the oven all the time".)

Daisy_A's picture
Daisy_A

Hi chuck,


Thanks for your message. Following this debate I'm not sure it's necessary to cure the stone. However the mix is water permeable. 


I store the stone out of the oven for convenience as it takes the oven a much longer time to heat up with it in. It's reassuring that the stone is not under so much stress with lower temperatures in domestic ovens. I was just wary as I had heard of so many pizza stone cracking.


Wishing you happy baking, Daisy_A

Daisy_A's picture
Daisy_A

Hi Zeb/Joanna,


That's looking good. Lovely breads too!


It's bigger than mine, then. I am currently working ways out to sneak two hearth loaves on! Our oven is very reliable but tiny. 


Some food suppliers talk about heating the stone up gradually. However few, if any, talk about preparing the surface. I got that from potter friends. 


Thought afterwards that I should put the dust issue in context. The fact sheet I accessed on mullite referred to miners who were exposed to quite large quantities of dust over many years. This is also more of an issue for potters,  as they have greater general exposure to silicates over years in the form of clay dust. 


Overall I've found the kiln shelf a cracking surface to bake on. I use two iron fajita trays underneath it to focus steam. Looks like you are getting a great rise on your loaves. Do you mind me asking what oven type it is and if and how you steam?


Wishing you happy baking.


Best wishes, Daisy_A

Zeb's picture
Zeb


Do you mind me asking what oven type it is and if and how you steam?


 



Hi Daisy, not at all. I have a Neff electric oven and it's taken a bit of getting used to. It goes up to 250 C and down to 30 C (useful for Detmolder!) . I steam by putting little Mermaid tray on shelf below and heating up at same time as oven, then pour boiling water in either before bread, when bread goes in, sometimes a second dollop. As the electric oven's mission in life is to get rid of steam, it is always a bit of a hoohah, but I think overall it makes a difference, least I hope it does.  I use the top bottom setting usually, unless I am making pizza and then I use the pizza setting which i think is bottom heat only. 


I once had the delight of using Rick Coldman's wood fired oven at Mairs Bakehouse when he hosted a baking weekend. I remember that when we made pizza we did that on trays which we slid in and out of the cavern of his oven, whereas all the breads went directly on the hearth floor. I have a feeling that the only time I have needed to scrape anything off the kiln stone was when I made pizza, all those wet toppings...I don't clean it, same with my baking tins, I wipe them out and if they have something like chocolate stuck then of course I get it off, then I put them back in a warm oven to dry completely. Seems to work so far for the bit of home baking I do.


Well done for answering everyone on this thread so methodically :)  take care Joanna


 

Daisy_A's picture
Daisy_A

Hi Joanna,


Many thanks for your response. This looks like a good set up for baking.


I've always has a gas oven but will consider electric in the future when it needs to be replaced. The gas oven has a moist heat but my model seems to heat less evenly than some electric ovens I have seen. We don't use it much as we now use a tagine on top of the stove to stew or braise. Bread making tests it the most, although I guess this is true of making hearth breads in domestic ovens in general. 


How great to have got to use a wood fired oven. Would love to do that. I will remember the tip for pizzas, thanks. 


It's also reassuring to hear that your stone has required little cleaning even with regular use. Thanks for that. I also tend to start to clean baking tins by wiping them and then just using water on what remains. Wasn't sure if this was a good approach so good to read that you approach it this way! I think I get the minimal or no soaking approach from cooking mostly with cast iron. 


Best wishes, Daisy_A

Noor13's picture
Noor13

I am in the Uk close to London as well :)


I got my stone from this site


http://www.pizzastone-shop.eu/


It might be a bit pricey, but I love this stone. Breads and Pizza come out wonderfully.


Take care,Noor

Noor13's picture
Noor13

Oh, and they have a special bread stone, not just Pizza stones

JBeddo's picture
JBeddo

There is no need to condition, season a kiln shelf to use it for a baking stone and they are food safe!

Daisy_A's picture
Daisy_A

Hi JBeddo,


Thanks for your message Ya lo se! The main reasons I did mine was not to render it food safe, as I'd checked that. It was to make the surface less friable, prevent sticking and prevents grease soaking into the surface and it has helped on all counts.


Apparently potters use kiln wash so that pots and glazes stick less :-). Just thought I'd draw on their expertise as they had been using the things much longer than me and I wanted to be doing the least oil and dough scraping possible! Haven't had to take a scraper to it once.


Best wishes, Daisy_A

geraintbakesbread's picture
geraintbakesbread

I use a 15" x 13.5" x 1/2" (38cm x 34cm x 1.5cmkiln) kiln shelf. I got mine when I was on a course with Paul Merry at Cann Mills in Shaftesbury - he had a pile in a shed in the back yard! If I need another, I would contact Bath potters as many of you have suggested.


I previously used a granite chopping board that I'd heard recommended by Richard Bertinet amongst others. It lasted about 4 bakes before cracking & I felt imparted a weird taste, but that might have been paranoia: apparently it has low level radioactivity & releases some sort of gas? (I can't remember exactly, as is obvious!)


I usually use the top oven on my cooker, which is 17cm(6&3/4″) floor to element. I manage to fit a grill pan (for adding water for steam) on the bottom & the kiln shelf on a rack immediately above that.



Oven Set-up by sgratch13, on Flickr


I’ve cooked up to 1 x 1.4kg or 2 x 6-700g freestanding loaves in this oven. Although it doesn’t get quite as hot as the bottom oven, it still gets above 250c (482F) & the temperature is much more stable. Also there’s no fan, so all the steam isn’t immediately pumped out.


I never thought of coating mine in spite of having a ceramcs degree! Still, food bits are easier to scrape off than melted glaze, the primary reason for coating them in slip.


Do you get any smoking from yours Daisy as a result of the wash you put on? Does it resist oil e.g cheese from stray pizza topping? (I've yet to acihieve a really crispy pizza base with this set-up, 'though I've come pretty close.)


I don't believe brick/stone based commercial/wood-fired ovens are coated with anything though? Isn't it good that the stones can absorb moisture, e.g. isn't the base of a wood-fired often swabbed before loading as a sort of steam injection?


I think flour dust is more likely to cause most of us harm way before any from the kiln shelves!


I'd be amazed if any were to crack due to thermal shock in a conventional oven - in ceramics, pretty much the lowest temperature these would be heated to is 1080oc (1976F). However, they are somewhat fragile & can crack easily if accidentally knocked & they are best left in situ IMO. I wouldn't think it necessary to store them on their sides - this might have something to do with preventing warping, not an issue at domestic oven temps.


 

Daisy_A's picture
Daisy_A

Hi Geraint,


That's a grand looking set up! Bigger than mine again although I am working towards slipping 2 x 600g batards onto mine. I need practice, though as if I don't get it just right second loaf starts sliding elegantly off the stone.


Know what you mean about flour dust being more of a danger Didn't focus on that so much as apparently some bakers do get 'baker's lung', sadly. 


Think stone might have smoked first time as that was effectively 'baking' the glaze. No smoke at all now. I used flour, water, starter to the consistency of slip. Will put up the pictures when I can access them again. I did make it a bit darker when I cooked pizza.


I know what you mean about the stickiness of glaze. However some of my early proteolytic doughs, including the one that went over like a Dalí clock face, were mighty sticky and pulled off without using a scraper! 


I haven't done pizza too much. I imagine that there would be a greater resistance to oil, though not 100%


I think you're right that wood fired ovens don't get coated but thought I'd give it a go. The water, starter, flour mixture does fill in the tiny pores of the stone which probably does help counter sticking, although I'm sure kiln shelves also work fine without.


Did think about the absorption thing. However my assumption was that it would work like casein paint and still be 'breathable' if you like, rather than a waterproof seal like acrylic. I think the stone could still absorb water and then dry, like a stone cottage wall painted with a thin casein wash. (Our potter friend also built his own stone house in Yorkshire and used casein paint. It was then bought by Patrick Stewart. Weird thing is he looks like our friend...However our friend P. did tell us about casein paint as well as some pottery things.)


Don't always leave my stone in as oven is old and seal needs replacing so it takes ages to heat up with the stone.Take your point about not as high as kiln temps. That's a reassurance on the fracturing front although i do hear lots of tales of thinner pizza stones cracking.


I also store my stone on its side so it takes up less room in the tiny passage beyond the kitchen. The kind you get in older UK houses, that also has the bike etc plus a few dogged herbs! 


I'd go to Bath Potters again. I think they are selling the same or a similar product to some of the food companies, but for a lot less. Their packaging was also awesome. My 10x15 shelf arrived in a package the size of a small chest of drawers, that was completely filled with packaging materials.


Hows the BBA challenge going? I took Larry's cheese bread challenge. Don't do yeasted breads normally but it was awesome! 


http://www.thefreshloaf.com/node/21126/christmas-breads


Best wishes, Daisy_A


 

Daisy_A's picture
Daisy_A

Oh yes, it's coming back now. The other reason I decided to coat the kiln shelf in 'starter slip' is because I had observed already how resilient it was as a coating.


I started my sourdough culture in Jan. 2009 at 100% hydration with white plain flour. Have since changed it to 67% half wheat, half white - which makes a putty like dough, which suits me much better.


The early starter took a while to be ready for baking. I tried to recycle as much of it as I could in pancakes etc. However one night I got totally sick of trying to prize out the sticky, gooey mess at the bottom of the jar once again and so in less green fashion, rinsed it with water and threw it out the back door, under cover of night, onto the gravel soakaway at the back of our house.


Several weeks later, after the 4 seasons in one day that is the British climate, it was still there coating the gravel, having not soaked into it at all! It was at this point I, decided you could probably paint something with it, possibly even the house...


Daisy_A

geraintbakesbread's picture
geraintbakesbread

Hi Daisy


Is casein the same as limewash?


True, slip, same as flour water/wash, would be breathable. Might give it a go, as do get things sticking from time to time (notably aforementioned pizza toppings).


Not sure what pizza stones are made of, but generally seem to be quite thin: it probably doesn't take much of a knock to cause a hairline fracture which is exacerbated to a crack in the oven.


I occasionally have to move my shelf in order to fit a Le Creuset casserole into the top oven, but usually just store it in the bottom oven! (which we hardly ever use).


I have thought about getting a second stone and baking double-decker style in the bottom oven. I've only tried this with kiln shelf on the bottom & a loaf on a baking tray above it, but the results were unsatisfactory, esp on the lower loaf. Maybe I should try it the other way around, or as I say, get another shelf; the 'stone' might then act like the roof of a brick oven? Still, I think the biggest problem with the larger oven is the fan.


Sounds like it's time you treated yourself to a new oven! It would pay for itself in no time if your current one is so inefficient!


BBA #2 up this weekend: Christopsomos (Greek Celebration Bread) - we'll see how it compares to Panettone ;)


(Btw, still enjoying the last few bits of Panettone from 2 weeks ago, good as ever)


Also baking a couple of Hamelman formulas: Ciabatta with stiff biga and Semolina bread w/soaker & fennel seed; probably a sourdough too.


Last full week at the cafe over, just a few odd days over the next couple of weeks to do (plus tax returns & helping to get my partner's dissertation typed & organised!), then hopefully all systems go with the bakery project.


Any breads on your agenda this weekend?


All the best


Geraint


 

Daisy_A's picture
Daisy_A

Hi Geraint,


I think it is like lime based paint but it is milk based so the lactic acid in sourdough culture would be similar.  Can be used on stonework and also for tempura. Apparently widely used by artists before acrylic. However it is  also breathable and therefore better for old buildings. Lime and casein can be used together to make paint, apparently.


Replacing the oven will be tricky as it is built in to a lovely wood surround to match our old dressers. However it is the owners that are inefficient too! It's never let us down but I never tested it so much before breads. Needs inner and outer door seals replacing and light bulb changing.These are regular maintenance tasks you feel you should be able to do yourself, but which can go so badly wrong! Hope it will retain heat much better after seal replacements. 


Glad the panettone is still good! Have seen some of the Greek breads. Look interesting. Look forward to seeing your posting on those. Caught your anadama bread. That looked good - lovely burnish on it. 


Glad the bakery project is good to go. Tax returns and dissertation though - good luck with those then...Painful but doable if I remember correctly.


I have recently returned to Tim's (breadbakingbassplayer's)bread with 3 levains via Farine and Bread Team America. Lovely flavour. I will probably do that again.


http://www.thefreshloaf.com/node/19501/9510-51020-pain-au-levain-and-walnut-raisin-bread


Contacted Inoxss re pandoro moulds. Just waiting to hear back from them. 


Wishing you happy baking! Daisy_A


 

dscheidt's picture
dscheidt

Potters are not bakers. 


There's no reason to put garbage, which is what your slip is, on a stone.  There are all sorts of reasons not to, one of the big ones being "Do you want to eat burnt flour?".   Corderite is non-friable, there's no dust from a fired stone, unless you break it.  (There's probably some on it when it's new, but once that's cleaned it's gone.)  There's no need to oil it, season it or do anything but let it get hot and put a loaf on it. 


Bakers are not potters.


Nor is there any reason to flip it over, store it on its side, or do any of that magic.  If it's convient to store it on its edge, fine, you won't hurt it, except you increase your chances of dropping it.


Rember, a *cold* kiln firing gets to 1100 F (about 600C).  A hot one hits 2400 (*1300 C).  A hot oven gets to 600F.   Stress failures are very much a function of the temperature and rate of change.  You're not going to damage a kiln shelf with a home oven.

Daisy_A's picture
Daisy_A

Hi dscheidt,


Take your point. The flour and water is not slip and it can burn. I blackened it when I overcooked my first pizza so other bakers may not wish to do this, a point I was set to make today before you made yours. However it is not friable and I am not eating it. Moreover I nearly carbonized the pizza so don't think it would have done an uncoated stone any good, either. 


Each to their own. I have hesitated posting on this before because the flour can darken the stone. However I was just adding my view to the general discussion and was asked to do this. If bakers don't want a darkened board they don't need to do this. Discussion with some earlier posters suggests that this may not be necessary, which is a useful clarification.


I get some burnt flour anyway as I flour well when peeling. Don't see how that can be avoided although it concerns me and I've thought about reducing the amounts. I assume that any flour in the oven is only going up to the around the temperature that the loaf itself will cook at initially. A loaf's own crust is caramelized, even blackened at times. One would need to not bake to avoid eating any blackened flour at all.


However I don't agree with your 'hot' leading point; flour, water, starter is not 'garbage'. It's what we cultivate and eat.


As said above I also store the board on its side because it is more convenient. I don't flip it. I don't see it as 'magic'. I try to take information from various sources and weight it up. Much of this debate has been useful. 


In the reply to Geraint I acknowledged that I was reassured that domestic oven temperatures were not likely to crack the stone. Points don't have to be made aggressively to hit home. However thank you anyway for confirming this information. Nevertheless, when I first got the stone, I had heard of many pizza stones cracking and wanted to do what I could to protect mine.


I had to translate the information I had as I got this from very helpful pottery suppliers.


However I think there are potentially greater dangers when buying pottery stones for baking from non-potters. I outline these below.


Bakers aren't potters; you're right there and that causes problems of its own.


At least one non pottery, non baking European retailers supplies what are likely to be kiln stones for baking. They also give advice on cleaning and sanding the stone.


Pottery suppliers advise wearing a mask when sanding kiln stones because they know their trade and know that this can release fine silicate dust from the stone


The non-pottery European retailer advises scouring persistent stains off stones with stainless steel scourers and sanding down the stone from time to time with sandpaper.


This can release silicate dust but no mention is made of wearing a mask. You don't have to have an industrial disease to find this problematic.  If you have asthma you wouldn't have to do this for long before risking problems with your breathing. 


As you say dust is not released normally from the stone, only if it is broken. However the same site also states that the stones they supply are brittle but can still function if edges are broken and that this has no negative impact on their functioning. Their own site shows stones arriving broken in transit by hired couriers. They advise contacting the couriers about this problem but no mention is made of potential dust release. 


I find this much more problematic than any dealings with flour and water. I can't see how anyone relying on that information alone would be cleaning the stone safely. The information from potters really helped in that respect.


I'd rather take flour in by mouth than inhale silicates due to reliance on non-speciaist cleaning advice. I also feel such problems come directly from non-pottery retailers not taking on board the expertise found among many potters and pottery suppliers.


This and the much cheaper cost for what looked to be the same item were the main reasons that I chose to buy my stone at a pottery supplies shop. It's been great to use and I am learning more as I go, but I won't be sanding it. 


Sincerely, Daisy_A

Mini Oven's picture
Mini Oven

is a lot to do over nothing.   Sorry, pottery and bread are similar but not the same.


Kiln shelves are not affected by kitchen oven temperatures.  The temperatures are too low.  By conditioning a shelf or stone all what is needed for the home baker is just to gradually warm it up for the first time slowly to dry the thing out.


These shelves are ment to take 600°C (1112°F) plus temperatures which is molecularly hard on the atomic bonding of the stone and that is when special care is needed to flip shelves to prevent sagging.  They become more brittle with the number of high temperature firings that they live through.  Coating them with a wash of kaolin and alumina hydrate (slip) is done to prevent the molten glass from glazes, melting clay bodies and melting metals from bonding into the shelf, which would be a real pain to clean for it would requiring chipping & grinding.  It has to be cleaned off or it will melt and bond to other pots when the kiln is reheated.  This has all to do with ceramics.  Grinding or sanding this hard a surface would be better done with a water cooling grinder... no dust.


A mixture of kaolin and alumina hydrate has a very high melting point and therefore used (like you would rice flour) by potters to prevent sticking.  One very big difference: Flour on the stone will burn!  Kiln wash on a kiln shelf will not burn and remains intact but any drips of glaze or molten metals can be removed or flaked off -- the dried wash sticks and bonds to it preventing running and a bigger mess.  Unlike a kitchen oven, a kiln cannot be instantly opened and the pots removed, it will be days before that kiln is opened.  When glaze or the stuck pot is removed from the shelf, part of the coating is removed too.  The spot is touched up and filled with a quick brush or two of slurry and allowed to dry before the shelf is used again.  The reason for layers is again so that the stuck on piece of pottery will come off easily and remove only the last layer of dried wash.  Several layers protects the shelf better than one layer.  This is for pottery.


Now, if you want to apply this theory to your baking stone, I suggest you get a mineral powder that will not burn in your oven and is approved safe for consumption.  The whole idea of coating the stone is not needed in a home oven.  Molten sugars and such will burn up and out on your stone over several bakes.  Parchment paper would be the best protection for those who want a spotless stone.  Flour dust is very harmful, and on a semi-daily basis, more so than sanding a stone one a year.


Warning: What one should not do is use a used pottery shelf that has been used for ceramics.  Invest in a new one.


Mini

Daisy_A's picture
Daisy_A

Hi mini,


Thanks for the advice. My stone hasn't been used for ceramics. It works fine.


I agree there's no need to make a fuss. However when researching what baking stone to get I was a novice baker and I came across a lot of 'hot' threads on TFL and elsewhere talking about various materials adapting for baking being explosive, toxic etc. It did worry me so I took care to choose something food safe.


Don't know what it is about stones that gets people going but it does! However there was a lot of fuss around stones already and I was concerned to get something safe.


I had no wish to contribute more to stone fuss, which is why I did not post before. As said before, I was asked to say what I had done to my own stone so responded on what seemed to me to be a pretty genial thread compared to many others on oven stone topics. As also stated I had already thought that the flour blackening might be a problem. 


Some posts on this thread, including yours, have reassured me that the heat of a domestic oven will not crack a stone. However, here again, when I set out to get a stone,  I had heard of many stones cracking in domestic ovens, even those sold as food safe.


I have seen electric kilns fired regularly and even helped build and fire a kiln for raku a couple of times and seen the pottery emerge still flaming! I know there is a big heat differential in temperature between these and a domestic oven. However having heard of so many stones cracking I was still unsure how my own stone would fare. It has been robust so far, thank goodness. 


I have already acknowledged that coating may not be necessary and that has been a useful and reassuring aspect of some information on this thread.  Will probably simply use the other side if I want something non-coated. I can't keep on buying new stones. 


What I'm not convinced about is that because bakers are not potters that no advice crosses over well. I know you are not saying this but I feel it is implied in some statements on this thread. 


I still feel that kiln stone suppliers for baking use that recommend scouring and sanding the stone without mentioning the need to use a mask are missing out vital safety information that pottery suppliers do tend to give because of greater current health and safety awareness in the pottery sector.


This has been hard won and comes from awareness that exposure to silicate dust should be minimized.


Sanding or scouring a stone without a mask won't expose the home baker to dust levels that potters encounter.However exposure to any dust can trigger breathing problems for those with allergies and silicate dust can be very fine and is a known irritant.


Knowing a potter who now has to go for breathing tests, I don't think this aspect is a fuss over nothing. I think safety advice about wearing a mask if sanding or scouring a stone transfers well here. It still concerns me to see it missed out by non-pottery suppliers who advise sanding and scouring as ways of cleaning a cordierite oven stone. 


Kind regards, Daisy_A

Chuck's picture
Chuck

I also find new kiln shelves work quite well for baking  ...provided you do not do any of the things that are recommend for ceramics use. Don't try to coat it with anything. Don't apply any sort of "slip". Don't do any break-in procedures. Don't sand it. Don't try to clean it.

If you do any of the sorts of things typically done for ceramics or that almost any well-intentioned potter or ceramics salesperson will recommend or that are printed right on the directions that come with the shelf, you will both a) risk some serious health and safety issues and b) have a poor baking experience. Those are all "ceramics" instructions, not "bread" instructions.

The solution for bakers is very simple: let everything that potters tell you and everything the directions that come with the shelf say go in one ear and right out the other.

Daisy_A's picture
Daisy_A

From useful debate on this thread seems like kiln stones should be safe for home baking with wiping rather than coating and that they should be able to withstand home oven temperatures given that kilns are so much hotter than home ovens. 


That all feels reassuring given the dire warnings about baking stones in general that I came across when trying to choose a stone for home baking


However at least one international supplier mentioned on this thread does advise the sanding, scouring approach to cleaning. Might be best to give that a miss?


Would definitely use a mask if choosing to sand a kiln stone. Don't think this is OTT with silicates, given that it's mostly standard advice in the UK now for any sanding tasks that release fine dust.


However I don't know how far we have got on the initial question which was about baking stone suppliers in London? Bath Potters seems nearest with good prices and at least one online alternative has been suggested.  Anyone know of any good suppliers nearer to or in the 'Big Smoke'?


Daisy_A

Chuck's picture
Chuck

I've been following with interest the information about sanding down cordierite and the danger of silicosis. The simplest solution for bakers is simply: don't (not "be careful" or "wear a mask" but simply don't).


(While advice about "kiln shelves" or from potters can be reasonably crossed over to the baking world given sufficient thought and care, on balance the danger of carelessly translating [irrelevant] ideas like "sand the stone" seem to outweigh any possible advantages.  ...I'm pretty sure the original "sand the stone" advice came from either a "kiln shelf" or a "pottery" source, not a "baking stone" source.)

Daisy_A's picture
Daisy_A

With you there Chuck. This advice is currently on a baking stone supply site. However it is not a baking site as such and doesn't show wider knowledge of baking in general.


I agree that the advice on cleaning was probably taken originally from advice to potters and it missed off the essential safety advice relevant in the pottery context, where stones dirtied with glaze might be sanded. I also think it is not relevant to use of the stone in home baking.


My concern was that this 'cleaning advice' was out there on a site from which home bakers were buying stones for baking and that they might regard it as authoritative.


I think your comment is very valuable. My simple line would be 'don't' also.


I was also reassured when Zeb commented on her stone, saying that it needed little cleaning, even after regular use. 


Best wishes, Daisy_A


 

Mike_Vienna's picture
Mike_Vienna
Salilah's picture
Salilah

I had a spare granite "worktop protector" so took the rubber feet off it, and used that

Probably not as good as stone, as it won't absorb - but it shows no sign of cracking - they are currently £10 from Tesco

cheers
S