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I'm working on a trompe l'oeil porcelain wedding cake. The clay is Laguna cone 10 and has their added plasticizer.  Porcelain doesn't behave like sugar and shortening, of course, and sometimes crumbles when I try to extrude elements.  Can I add some sugar based material like corn syrup or regular sugar or maybe something like gelatin or agar agar to make the clay stick together better?  The additive or any mold that grows on it will burn out, but could it cause problems with drying or pitted surfaces?   I don't plan to reclaim any scraps.

Cynthia

Wcake 1 .jpg

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You might try adding a product called Additive A. It's an organic plasticizer and it is especially useful for extruding. I have not used it but from what I have read, it increases plasticity without increasing the water of plasticity. There is plenty of information online about it and many suppliers carry it.

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Nice work Cynthia. 

Given they added plasticizer, and it is still cracking while forming: makes me wonder what plasticizer they added. You could experiment with kayo syrup, but I suspect the tackiness will create issues of its own. Suspect the particle sizes of the kaolin is too large: not to mention larger particles are more prone to surface tension. Moisturizing the clay with a mister would help; but that comes with the price of higher shrinkage values. Keep it covered to impede drying as much as possible. You can take small pieces of clay and moisten them and let them hydrate over night- would help some.

tin: additive A is a polymer ionic binder. It would be classed as a deflocculant  in our little world. Darvan works on the same principle of negative ionic repulsion. It does work, but Macaloid would be more that suffice. If they added plasticizer and it still cracks: makes me wonder?

T

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(Can I add some sugar based material like corn syrup or regular sugar or maybe something like gelatin or agar agar to make the clay stick together better? )

keep the food stuff out of clay and use ceramic based materials to get your results-you are not baking  or using food here -its clay

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I once saw someone making ceramic baskets out of woven strands that were similar in thickness to some of your piped strands. They were using paper clay, and even allowed visitors to handle the greenware just to demonstrate how sturdy the paper clay was. I don’t know what type of paper fiber they were using, I imagine it was something where the paper particles broke down very small. Maybe somebody else here could recommend the right type of paper or fiber? 

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In re-reading this, I don't fully understand what you're doing. When you say extruding, are extruding coils of moist clay or using a piping bag to squeeze out slip? Can you describe 'crumbling'? If you're extruding moist clay, it probably just needs to be softer. If you're piping out slip, then I'm not sure how that can crumble, since crumbling to me means it would have to be fairly dry. Is is falling apart as it dries?

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The cake will be fired.  It is a lidded container, thrown in one piece.  Right now I'm not planning to glaze it and I'm trying to decide between cone 10 reduction or cone 6 oxidation.  I don't have my own kiln and the university where I take a class has both gas and electric.  The cone 10 will fully vitrify the clay and pretty much seal the surface without making it uncharacteristically shiny. But the reduction will give the unfinished porcelain a gray cast.  I'm thinking of adding a little pearl luster for accent later.   The cone 6 oxidation will keep the grolleg white, but the surface will be more porous.  I'm thinking about clear or white matte glaze at either temp.  If you have a good cone 10 matte white or clear, or know where to find one, I'd appreciate your help.

I've been using both a cake decorating bag with tips and a mini syringe type extruder.  The roses are made by squeezing a ball of clay between my right thumb and the palm of my left hand, then rolling the petal.  This is where the crumbling is the worst.  When I tried to make them the standard icing way, the slip was either too firm to go through the bag, or too soft to maintain its shape.  The leaves were easy to make with the cake tools.  The strings were the hardest and I didn't make as many  or as thin as I wanted.  I made the strings on a flat surface, then moved them to the side of the cake.  High failure rate with that.

I'm planning to add a gallery of some kind to the top to hide the line of the lid.

This is a time consuming winter project.  After this I think I'll make a few dozen little things for the craft fair season.

Cynthia

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Gets tough trying to remedy clay problems when you are almost done. Cutting up the remaining clay into 1" cubes: mist heavily and seal in a bag until its rehydrated. Quickest, simplistic fix. Sounds like your clay dried out over a period of time working with it. 

Coleman porcelain uses macaloid as a plasticizer: creamy and dreamy when fresh. If it gets old: not so much. Given you are working in a class, I suspect the clay selection is limited. Nice piece, do not let a hiccup deter you.

T

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Maybe the working roses by hand is dryinh out the clay moreso than the extrudingg and piping method. So making the clay for those parts a bit wetter may solve that problem.

Whew A big project..

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Porcelain is the least plastic of all clay bodies, and dries very quickly. Work wetter. Also, if the base is leather hard and you're attaching long wet coils, those coils are going to shrink more than the base and crack. So I recommend making the coils and letting them set up in their shape before attaching.

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Your cake decoration reminds me of the fine baskets being made by Belleek Potteries in Ireland. They work gum arabic into the dry porcleain clay and extrude very fine coils to make their baskets with. They say that without the gum arabic it would be impossible to make the fine detailed work. For the flowers they use the same clay and  olive oil on their hands. Excellent video of their process here, the basket ware starts at around 6 minutes in. 

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Cynthia:

The best plasticizer available in the USA is V-gum T. It will do what you were hoping the syrup would do in your original post.I mix my own clays, and use it in speciality porcelain bodies I use. However, it is very rarely used in  commercial bodies due to the price point. If you are going to continue making these types of pieces; then it would be worth purchasing 1/4lb. You need very little: and  very little will extend drying time and greatly improve plasticity. In addition, you can mix one cup at a time and add to your clay as you go by simply wedging it in. If you have gums available that are typically used in glazes: that will also work. There is another product Mark C. Uses: Magma?  Mark can weigh in on that one. Additive A is not the best option in this case: although it does work. Remember to blunge V-gum separately and add to your clay as you go. 

If you are going to continue to make these kinds of pieces ( you should), then I would consider buying dry porcelain clay mix and adding V- gum T to it as the plasticizer. Mixing 5 pounds of clay at a time does not require special tools. More work- yes, but given the type of work, it will solve a big problem. As with all things clay: some rabbit holes require their own solutions.

T

 

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3 hours ago, Min said:

Your cake decoration reminds me of the fine baskets being made by Belleek Potteries in Ireland. They work gum arabic into the dry porcleain clay and extrude very fine coils to make their baskets with. They say that without the gum arabic it would be impossible to make the fine detailed work. For the flowers they use the same clay and  olive oil on their hands. Excellent video of their process here, the basket ware starts at around 6 minutes in. 

Ooh thanks Min! The work I was talking about above was by Belleek Pottery, and it was gum arabic not paper clay. Thanks for refreshing my memory. 

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