Prevent Unglazed Wares From Sticking To Each Other

[soilandpolish]

Hi, this is my first post and I'm so glad to have found this forum!

 

I have only a test kiln, so space is limited. I'm firing unglazed cone 6 porcelain pieces, all cylindrical and of similar size (each about 100 grams fired).

 

I want to stack them directly on the kiln floor without the wares sticking to each other. Initial experiments with imperfect forms suggest that sticking will be a problem in the next iteration, when the forms will be more perfectly cylindrical and have greater surface contact areas.

 

I had thought to use kiln wash on the wares themselves to prevent this, hoping to remove the wash with minimal effect to the finish of the pieces. I could just try this ... but I could also return the unopened bag of wash if, as I'm beginning to fear, the wash will adhere strongly to the wares...

 

The pieces could be burnished or roughed going in, it's no great inconvenience either way. But power grinding post-vit would be over the top.

 

Maybe some other substance would suit this purpose better? (This kiln wash is the standard 50:50 kaolin:silica combination.)

 

Ideally, the wash would crack off like a husk, with no bonding interactions with the wares whatsoever.

 

Just read about "shelf paper" for the first time today, and maybe some corrugated wrapping pattern with that stuff would work better? Or would it still bond?... (Today I read in a post on this forum that it's only used for glass, so probably bad idea? And then I read that you could use it but it's a particular health hazard?)

 

Maybe the finish including bonded wash, with a quick sanding, would be acceptable.

 

I could sort of stilt the pieces, placing little interstitial balls of clay -- pretty labour intensive loading, but that would reduce the contact area. But then sagging might be a problem there.

 

Any suggestions will be savoured!

 

Andrew

 

[Min]

If porcelain pots are sticking to shelves or in lid galleries the usual solution is to add alumina hydrate to wax resist. I'm not quite sure I followed what you are trying to do, firing unglazed pots touching together? If you really want to do this then brush the alumina/resist mix between pots at contact points. Approx 2 or 3 tsp per cup of wax resist. 

 

It's a good idea to fire on a kiln shelf not directly on the kiln floor. A lot cheaper to replace a shelf than a kiln floor, plus the floor is usually a bit cool so raising it up 1/2" or so is a good idea. You can use a thin layer of alumina hydrate on your kiln shelf to prevent the the pots plucking, or use wax resist on the bottoms of the pots and put a shallow layer of alumina hydrate onto a flat surface and press the bottom of the pot into it before the resist has fully dried. The alumina will stick to the resist.

 

Min

[Chris Campbell]

A picture of what you are talking about would really help a lot ... its hard to visualize. Its another one of those "It all depends ... " questions. In some cases you can use kiln wash, in others some alumina mixed into wax ... and yes, you can use the kiln paper if you also use a breathing mask when you cut it or work with it loading or unloading. Can you post an image so we can give you a good answer?

[soilandpolish]

Thanks Min and Chris.

 

I think this image will give the idea:

 

... um, I created an image to illustrate but I can't figure out how to upload it.

 

Picture a bundle of drinking straws, or (perfectly cylindrical) logs. Long small cylinders, piled lying on their side.

 

There is no glaze so I'm no worried about the bottom of the kiln, should I be? As said it's a test kiln, so there's not really furniture available for that. Maybe I could get one made in a kiln that can go to higher temperature, or get a shelf cut. It's internal size is only a cube 6 inches wide.

 

My main interest is how to coat wares in a case like this, that have a large contact area with each other, and are densely packed, so that they won't vitrify to each other. Some coating that can be removed by mild cracking off or mild abrasion at the most (or even say a soak in vinegar or something...).

 

The idea of a wax/alumina hydrate (AlOH3) coating sounds attrative. So this stuff would not adhere strongly to the wares? Maybe I could even spray a thin coating of liquid wax, then dust with alumina hydrate with a ponce?

 

This link shows something like what I had in mind with the shelf paper:

 

http://www.conwedplastics.com/files/7813/5837/1302/snakewrap.jpg

 

(not supposed to hot-link images directly). I don't think this solution will work very well somehow, shelf paper is probably brittle? But even just horizontal layers of it might work.

 

Will 1:1 kaolin:silica wash stick to a typical cone 6 vitrified porcelain body, in the absence of any glazes?

[Min]

Thanks for the more detailed explanation. Are the items hollow or solid? If the former I'm guessing you are going to have them slump during firing, if solid they should be okay. Chris is the porcelain expert, she would be able to answer this better. 

 

No, alumina hydrate will not adhere to the wares. I would put it on thickly and use a higher amount of alumina, it will just dust off when fired.

 

I have never used shelf paper, no idea if it would work.

 

Min

[Chris Campbell]

Ok ... If you are firing to cone 6 you might not need to do anything depending on your clay body. I used to stack unglazed ornaments and whenever any small spot stuck I would use a small jewellers screw driver to click it apart with no breakage. The trick is to go slow when they are totally cool ... but i hate to say that I was 100% sure. What clay are you using and is it cone 6?

[justanassembler]

I know some porcelains vitrify a bit much when six is pushed further than a hot five/just down six...  if this is the issue, firing a half cone lower might be the solution.

[OffCenter]

Min is right. Go with the alumnia hydrate. I wouldn't even bother using wax; just use a lot of alumnia hydrate. As long as you don't get it on the elements it's not going to hurt anything and if you don't have a shelf you should cover the bottom of the kiln with it to protect the floor. (You really need a shelf on the floor even if it is just a thin tile that you make yourself by mixing some alumnia hydrate in the clay.)

 

Jim

[Marcia Selsor]

you could brush a thin wash (with water) of the alumina hydrate on the pieces. It washes off easily after the firing.

The wash would help it stick to the piece. and do start with a shelf as Jim says.

 

Marcia

[JLowes]

If at all possible, I would recommend firing those standing on end rather than on their sides, particularly if you need them to remain round.  Cone 6 porcelains I have used will tend to slump at vitrifiying temperatures and upright forms would not have any weight other than their own to support, laying on their sides, the bottom row will have all the weight above pressing down wanting to make them ovals.  Other recommendations about keeping the ware from sticking to each other and the kiln are wise.

 

If your kiln is a cube, then they should theoretically occupy the same space standing or laying.

 

John

[soilandpolish]

Thanks for all the input!

 

Min and John: The cylinders are basically solid, although I'll be trying all kinds of stuff, it's my first kiln.

 

Chris: I'm using a few clays. Right now, it's actually Plainsman M340, a cone 6 stoneware. I would prefer to use their P300, a cone 6 porcelain with lower porosity, but I have none at the moment. I also have some cone 6 casting slip from the same company, but haven't gotten started with mold-making yet. Thanks for the information about "clicking apart" bonded wares. I used my fingers on the stickers last time, but I expect a lot more surface contact area the next time, and especially if I start casting or extruding....

 

In case anyone has feelings about casting (versus throwing etc.), let me just say, I'm not aspiring to be a production potter, more of a mad scientist type with a love for ceramics. So techniques will be all over the map (if I persevere).

 

John: Actually I'm making use of the diagonal length on the floor, so firing standing would limit my length to about 70% for the biggest pieces. I have fired some standing, but found that they would warp from the heat, I think due to receiving more radiant energy on one side than the other. Have considered building a box of refractory clay to shild them, so could fire a lot standing on end, but I don't have a refractory clay or a kiln hot enough to fire it, so looking for the interim solution.

 

Jim: I didn't know I could mix alimina hydrate with clay to make my own bottom shelf. The kiln is rated for cone 8, but I bought used and have only seen it bend a Orton cone 6 in the sitter. I guess the alimina-clay mixture would not be suitable for making other kiln furniture? Or could you? It would be like playing doll house, making furniture for this little EvenHeat.

 

How thin could I go with that alumia-clay floor shelf I wonder?

 

Marcia and Jim: Great! Not having to use wax is great, as my ventilation consists of a bathroom fan.

 

justanassembler: Yes. I guess I'm looking for decent strength, low absorption, but trying to prevent warping. When I get to using porcelain again, I may try this. It's a sitter-type kiln. Can I use a cone 6 cone but just nudge it over a bit so the guage sits on slightly thinner part of the cone?

 

Min, Jim, Marcia: Thanks very much, this is what I hoped -- that something (alumina hydrate) will not adhere to unglazed wares. I thought maybe the maturing clay would "sweat quartz" or something, making anything stick.

 

Alumina hyrdate sounds like really useful stuff, can protect kiln floor until get shelf, can keep wares from adhering, and can maybe make my own kiln furniture...  probably I should try to exchange my 2.5 kg of kaolin:silica wash for alumina!

 

Thanks again to all of you for kindly sharing your knowledge/wisdom/experience!

 

Andrew

[Chris Campbell]

You could build your own little trays to hold and support each one and design them in a manner that they stacked. Then you would just have to use kiln wash on the trays instead of on the pieces.

[soilandpolish]

That's a great idea, thank you! It would be easier than trying to make furniture which allowed me to fire them upright (which has the warping problem anyhow).

 

In my situation, if I wanted to make say a bottom shelf, and some trays, would I try to wedge like 30% alumina into some cone 6 stoneware clay, and get some Orton cone 8 cones and try firing it in this very kiln? Or would I need to slake my own clay from powders?

 

Maybe I should make cylinders out of this refractory [?] alumina-clay, for the firing of the trays, so that they keep the shape (like firing pots with the lids in place)?

 

I will research about alumina today, it sounds really useful, especially if I can make my own furniture. It probably won't be cylinders next month, who knows...

 

P.S. No home internet, so if my responses are slow sometimes that will be the reason. Also, I noticed the pinned post about attaching pictures, now I know to go to More Reply Options.

[Chris Campbell]

I think you are creating a lot of work for yourself. Just make some stacking trays out of a higher firing clay than the one you are using for the wares and fire to see if the idea is valid. Then if it works out and you want to make hundreds of them ... go for a more permanent, sturdier tray/shelf system. This way you won't waste a ton of time, money and energy on a bogus idea. A test run might also show you ways to tweak the design so the final one works better.

[jrgpots]

I think you are creating a lot of work for yourself. Just make some stacking trays out of a higher firing clay than the one you are using for the wares and fire to see if the idea is valid. Then if it works out and you want to make hundreds of them ... go for a more permanent, sturdier tray/shelf system. This way you won't waste a ton of time, money and energy on a bogus idea. A test run might also show you ways to tweak the design so the final one works better.

 

This might be one of those time wasting ideas, but hear me out.  I am making flutes and am making a honey comb-like furniture so my flutes don't warp or slump during drying or firing to bisque.  I made paper tubes and arranged them in a hexagon pattern as shown in the pic below, then used high fire casting slip with alumina to make the piece of furniture. This hexagon is currently being fired.  The greenware will then be placed in the honeycomb and fired.  No slumping or warping should occur.  It might be something to look at if you are making a lot of the same shape tubes.

 

jed

[soilandpolish]

Chris, yeah you're right, making more than one tray to start with would be silly. Or designing them to stack before I've even tested one. I'm more theory than practise, so overdesign happens (but you can save a lot of time at a higher level by that).

 

I'm thinking that, since the kiln is so small, custom DIY furniture is more feasible than for usual kilns: the weights involved are smaller (shelves and wares both), and space is especially tight, which justify some nifty trays and supports (like for more general use). Also it's unlikely I'll get a larger kiln for years.

 

I'm just not sure whether I can make the furniture in this ^8 kiln, let alone without buying/lugging a box of fireclay. Hmm... (including a cab ride one way, buying a box of proper fireclay is about $50 minimum investment) ... Would love if could make it with my M340 stoneware mixed with allumina silicate (for which I can exchange the big bag of wash tomorrow, spoke to the supplier). And fire it in this same little kiln. But, would hate for a big load a few firings down the line to smash down, if I could've avoided it by spending the $50!

 

jed: Yeah, that's a sweet idea. Is it a solid or hollow casting? That design looks like it really helps assure equal heating of all the wares over the whole firing. Will the flutes stand freely within the tubes, or do they lean slightly to rest againt the tubes?

[jrgpots]

Chris, yeah you're right, making more than one tray to start with would be silly. Or designing them to stack before I've even tested one. I'm more theory than practise, so overdesign happens (but you can save a lot of time at a higher level by that).

 

I'm thinking that, since the kiln is so small, custom DIY furniture is more feasible than for usual kilns: the weights involved are smaller (shelves and wares both), and space is especially tight, which justify some nifty trays and supports (like for more general use). Also it's unlikely I'll get a larger kiln for years.

 

I'm just not sure whether I can make the furniture in this ^8 kiln, let alone without buying/lugging a box of fireclay. Hmm... (including a cab ride one way, buying a box of proper fireclay is about $50 minimum investment) ... Would love if could make it with my M340 stoneware mixed with allumina silicate (for which I can exchange the big bag of wash tomorrow, spoke to the supplier). And fire it in this same little kiln. But, would hate for a big load a few firings down the line to smash down, if I could've avoided it by spending the $50!

 

jed: Yeah, that's a sweet idea. Is it a solid or hollow casting? That design looks like it really helps assure equal heating of all the wares over the whole firing. Will the flutes stand freely within the tubes, or do they lean slightly to rest againt the tubes?

The flutes can stand up if the furniture is vertical. They can also rest horizontally if the furniture is turned 90 degrees.

 

My furniture is a solid cast. But you could make a hollow cast as well. I also use this to dry my greenware to bone dry keeping them straight.