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KellyRainey

Ceramic Bakeware

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I am new to creating ceramic bakeware but my mother wants me to make her a tray to make lasagna and homemade mac n cheese in. Here are my issues:

1. I cannot afford to purchase a slumphump mold to make a plaster mold so I need an alternative method for making a mold (I am not a potter - do not have a wheel).

2. I have heard of using wood, stryofoam, the foam insulation one would use for insulating a house for a mold but I am not sure how big to make the mold for the amount of shrinkage to be taken into consideration. In other words, how deep - I was thinking 2.5" deep but not sure, how big should the area I will be slumping into or humping over be,etc.nI am looking for a 13x9 inch baking tray as the final result.

3. I am not sure what the best clay would be for functional ware like baking trays, plates, bowls, etc. Right now I am using Amaco Versa Clay #20 firing range 04 to 5 with shrinkage fired at 02 6.1%. It says it is extremely versitile and can be used for both handbuilding and throwing. I have been told I could add a grog to this clay if I wanted more strength when I was making a rather large sculpture piece but I am not sure I want to go through that since I do not have the equipment to make enough.

4. I only have local access to a few types of clay since I really cannot afford to have it shipped to me and the only place in town that sells clay only stocks a few clays and only stocks their store brand (Blick Studios) and Amaco.

 

Sorry for all the issues. If anyone could provide me with detailed instructions on creating the mold that would produce a 13x9 x2.5 baking tray (outer dimensions, inner dimensions, best type of material make it) I would be very appreciative. I know it might be difficult since I do not know the exact amount of shrinkage I am dealing with so if I could just get detailed instructions on how to do the math/calculation to determine size once I do find out which clay I should be using. If you have a clay in mind that I should use (keep in mind I really only have a store name brand Blick Stoneware, it can be found on their website or a few Amaco brands) the instructions with the clay type would be awesome.

 

I really appreciate any assistance and help I can get....

 

Thank you!!!

Kelly

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Finding out how much your clay will shrink at the temp you want to fire to is not too difficult.

Make a Ruler out of a small slice of it. Take a real ruler and mark off your clay in 1/4 inch segments so the finished work looks just like a ruler.

Then let it dry and fire it to the temp you want to use for the dish. Re measure with the real ruler and you can easily see how much it shrank.

Then you add that amount on to your measurements.

 

As to your slump mold ... You can even use a lasagna pan you have and drape it over that ... Just take it off as soon as it is firm enough to move or it will crack.

I have used the hard foam people use for insulation ... It comes in many thicknesses and it is easy to cut.

 

I don't know anything about those clays so cannot advise you there ....

 

One common problem for potters is that people/family will ask you to make things you don't usually make. They will ask a sculptor to make a mug and a mug maker to produce a wall of tile and a tile maker to build a bird bath .... they think all parts of pottery are pretty much the same.

 

Sounds like you are a sculptor ... Are you thrilled with the challenge and really are interested in creating a functional piece? Are you comfortable with making a piece your Mom will be using to carry really hot foods in? Is this an area of pottery you want to spend time mastering?

 

I ask these questions with a 'been there/done that' friendly smile.

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Hi Kelly,

I agree with Chris except I have always done shrinkage tests using centimeters.

I have used basic stoneware for baking. My clay usually had 10-12%. So you need to know what your clay will do. I am unfamiliar with most commercial clays.

 

I have written an article on slump /hump molds in Pottery making Illustrated.

Plaster is not expensive, but you seriously need to do some research, read some articles..you can go to Ceramics Arts Daily on this site and search their archives.

You can make drop molds easily by creating a negative space using a plywood cutout. That is the most simple thing I can imaging for your situation. You have specific ideas, but seem to lack the education or knowledge to execute them. Just starting looking into resources.

 

Keep asking, but research because we don't know what you already know and exactly what you need to know.

Marcia

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Finding out how much your clay will shrink at the temp you want to fire to is not too difficult.

Make a Ruler out of a small slice of it. Take a real ruler and mark off your clay in 1/4 inch segments so the finished work looks just like a ruler.

Then let it dry and fire it to the temp you want to use for the dish. Re measure with the real ruler and you can easily see how much it shrank.

Then you add that amount on to your measurements.

 

As to your slump mold ... You can even use a lasagna pan you have and drape it over that ... Just take it off as soon as it is firm enough to move or it will crack.

I have used the hard foam people use for insulation ... It comes in many thicknesses and it is easy to cut.x

 

I don't know anything about those clays so cannot advise you there ....

 

One common problem for potters is that people/family will ask you to make things you don't usually make. They will ask a sculptor to make a mug and a mug maker to produce a wall of tile and a tile maker to build a bird bath .... they think all parts of pottery are pretty much the same.

 

Sounds like you are a sculptor ... Are you thrilled with the challenge and really are interested in creating a functional piece? Are you comfortable with making a piece your Mom will be using to carry really hot foods in? Is this an area of pottery you want to spend time mastering?

 

I ask these questions with a 'been there/done that' friendly smile.

 

Chris,

You guessed correctly... I am a sculptor, so for the most part I have not had to worry about shrinkage too much. When I was in school I did learn about the shrinkage ruler and have a few for clay I made while in school (too bad I do not have clay left over from then (2003-2007). Many of the commercial clays I will be working with give me a shrinkage rate so I what I am really in need of is how to calculate the size I would need to create for wood, foam, etc mold so that when the clay shrinks the piece will be the 13x9x2.5 size that I want. Does that make sense? I have actually determined which clay I will be using and it has a 12% shrinkage rate at full maturation (which is what I need to fire at for functional oven ware). So, in other words, I know the mold I start with will need to be bigger than what I want the finished piece to be because of shrinkage but do not know how to calculate what size I need to make the mold to start with at a 12% shrinkage rate.

 

As for using another lasagna pan as a mold wouldn't I need to use a pan that is bigger than what I need in order get a 13x9x2.5? I get that if I use another pan that I have to take it off as soon as it is form because it will shrink and that will make it crack but is there a way to handle the size issue because of shrinkage at full maturation.

 

Yes, I am in fact looking forward to the challenege :-). It is something I have always wanted to do but never really focused on until now. I am told it would be easier for me if I created them on a wheel but as I said in my original post, I do not own a wheel nor do I have access and I have never learned :-(

 

Thank you for your help and "been there, done that advice" :-)!

 

Kelly

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Guest HerbNorris

Kelly, you're right when you say that you need a mold which is larger than your finished piece. How much larger? That always depends on the shrinkage rate of your clay, which in your case is 12%. So your mold must be 12% larger in all dimensions to give you the finished size you want.

To determine the mold size, just add 12% to each dimension of the finished size you want.

An easy way to do this is to muktiply (or multiply) each dimension by 1.12, and you will have the mold dimensions that you need.

So to get a piece that has a 13" finished length, you would multiply 13" by 1.12, which gives you 14.56". I'll leave it to you to do the other two dimensions.

If your clay shrank 8%, you would multiply by 1.08, 10% by 1.10, etc.

I'd make the mold 14.5, and then just ease the side out just a hair, to get the final 0.06" It's not that critical, kinda like making lasagna.

Marcia has a good point in that using metric measurements are easier to use as far as shrinkage calcs go, it's easier to measure centimeters and, if necessary, millimeters than parts of an inch. But whatever...

You need to catch the molded pan at just the right point of dryness, so that you can safely take it off the mold without collapse.

Just give it your best shot, and I'll bet it will turn out great! Besides, moms tend to be a little forgiving, and since this is the first time you're trying this, cut yourself a little slack.

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A good method to form this pan is by slab construction and using your sculpting techniques to refine the shape. Be sure your pan design has all of the necessary attributes: sturdy handles for easy and safe lifting, a foot on which to rest, and an easy cleaning surface. Also, if you go with this method do not roll the slabs out too thinly do not roll out under 1/4"; for shrinkage will be in all directions and a lasagna pan needs a little heft.

 

And finally, whichever clay you decide to use test it first for the shrinkage as mentioned, and for proper glaze fit.

 

 

 

 

 

 

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I've used blocks of wood as forms. I have some thick slabs, but have also stacked plywood and taped it with duct tape. When using a hump mold I always use a thin piece of foam between the form and the clay. The foam compresses as the clay dries and gives you a little leeway for clay set up. I also use tissue paper over the foam. If you are using a pan for a form the clay will stick like epoxy if you don't use some sort of release.

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Are you making a lot of these pans? if you are not, dont make a whole mold for just one pan... usually potters spend the time to make a nice mold when they know they will be using it for multiple pieces. find something to drape the clay over (much much much easier), like chris said an old lasagna pan or even just a 9x13. also, how specific do you really need to be with your measurements of the 9x13? i find clay to be something that is hard to truly measure, and it seems pointless in your situation. dont make the project harder than it has to be!

 

unless, of course, you plan to become a potter; then by all means make all the gadgets and gizmos to create your perfect pan.

 

remember, its just mud. amazing mud, but still mud.

 

ps - for a good release from draping the clay, i have used paper towels. some people spray kitchen PAM though, or dust with cornstarch. and again, i really wouldnt sweat the shrinkage. while 10-12% can be a noticeable difference, it most likely wont even matter. my guess is that 6.1% shrinking will put you out about an inch, meaning every side will be smaller by 1/2 inch. 8x12 pan. :)

 

pps - my math for that was 100%-6.1% = 93.9% or 0.939. then, 13(.939)= 12.27"

 

ppps - making a square/rectangular pan is not easier on the wheel. goes against physics...

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Are you making a lot of these pans? if you are not, dont make a whole mold for just one pan... usually potters spend the time to make a nice mold when they know they will be using it for multiple pieces. find something to drape the clay over (much much much easier), like chris said an old lasagna pan or even just a 9x13. also, how specific do you really need to be with your measurements of the 9x13? i find clay to be something that is hard to truly measure, and it seems pointless in your situation. dont make the project harder than it has to be!

 

unless, of course, you plan to become a potter; then by all means make all the gadgets and gizmos to create your perfect pan.

 

remember, its just mud. amazing mud, but still mud.

 

ps - for a good release from draping the clay, i have used paper towels. some people spray kitchen PAM though, or dust with cornstarch. and again, i really wouldnt sweat the shrinkage. while 10-12% can be a noticeable difference, it most likely wont even matter. my guess is that 6.1% shrinking will put you out about an inch, meaning every side will be smaller by 1/2 inch. 8x12 pan. :)

 

pps - my math for that was 100%-6.1% = 93.9% or 0.939. then, 13(.939)= 12.27"

 

ppps - making a square/rectangular pan is not easier on the wheel. goes against physics...

 

I agree don't worry about the size being perfect a little smaller could be better because of the weight, I have a ceramic lasagna pan and by the time it's full and hot it's a little hard to handle and I'm a pretty strong woman. Denice Wichita KS

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Thank you everyone. I appreciate all the input and feedback. I have taken note of all your ideas and will be starting on the pan within the week. I guess I was worrying way too much :-).

 

Thanks again!!!!

 

Kelly

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Follow up question for the experts on this - my understanding is that one of the trickiest parts of making bakeware is the clay selection and potential for cracking during use due to thermal shock (taking your pan from room temp to a hot oven and back again in under an hour).

 

My professor has told stories of complete casserole wreckage followed by a very messy clean up. Is that just an unwarranted scare-mongering? 

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Hi Kristina-

I actually do not think that is fear mongering, but there is much more experienced ceramicists here who can give you a more educated answer.

I *will* say, however, that this is a very old thread and in order to get the most answers for your question you might want to start a new post.

Welcome!

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