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Sara78

Best Approach To Obtain Solid Blocks

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Hey there, 

As I've mentioned above, I am interested to know your point of view regarding the best approach to obtain solid ceramic blocks.

The final piece let's suppose that will be a cube with 4.5 inches side length. My concern is related to the fact that being solid and not enough dry, will explode in kiln.

 

As far as I've read, the possibilities are:

1. - To cut directly the clay forming a cubic shape, let it dry enough and fired (a good enough method if we don't have custom shapes which will guide me to the method 2)

2. - Building a polystyrene extruded model, making a mold and pouring/pressing in it a well moist clay (clay + water, I'll have to find the right proportion), let it dry, fired.

3. - idem as above but using slip instead of well moist clay, pouring in cast, let it dry, fired.

 

Any thoughts?

Thanks,

 

 

 

 

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In my own work I like quite heavy pieces and solid pieces...the biggest solids I've done are about 3.5 sq.   I dry the heck out of them, single fired to ^6. No problems so far, but I am not well-versed in the pit falls as I "use" flaws and accept mishaps in my approach. If the body is well-wedged the surface will be very smooth--if I don't do a thorough wedge, I will get cracks/texture/holes (no explosions!) but I aim for that effect ahead of time. 

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Thank you for your feed-back.

3.5 sq it means 3.5" side cube ? sorry I am from EU not so familiar with the US units. 

How much in days do you dry the pieces before you fire them, could you be so kind?

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We can have in mind the above example in the architectural geometric shapes area. Some will need details and perhaps will be not possible to be obtained using just the cutting clay technique; that's why may b necessarily to be made using a kind of material somewhere between a slip and clay consistency I suppose ...poured into shapes.

 

I am looking for the right solution. Thank you,

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Build it solid , then cut it open and carve out the inside, put it back together and most definitely leave a pinhole for the air to escape. I would dry it and then dry it in the kiln. Rotate it to allow all sides to dry. And I would fire it up on some coils to allow any steam still in it to escape.

Marcia

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You are going to have problems firing any ceramic that thick. It is possible, but requires a long slow firing of at least 2 days. The problem is not only the drying of physical water to eliminate explosions from the phase change to steam at 100C, but also a chemical change in the ceramic that creates more water at around 450C-600C.

 

You are aware of the problem of the the clay form exploding if the interior is not completely dry. A solid block of the thickness you describe will likely not dry by itself just sitting in the open atmosphere. Rather, you will need to gently heat it in the kiln at 90C, just below the boiling point for water, for a very long time until the heat has penetrated through the entire block and evaporated all the remaining water. A point to remember is that as the water turns to vapor, it will leave the surface from which it evaporated cooler, so while you are heating it, it is simultaneously cooling itself by evaporation. It will take a long time for that moisture and water vapor to work its way out.

 

A second vulnerable period for clay is less understood. The theoretical chemical formula for clay is Al2 Si2 O5 (OH)4, or reordered to Al2O3 2SiO2 2H2O - which is one molecule of standard alumina oxide, 2 molecules of standard silica oxide, and 2 molecules of standard water. At red heat, the molecular bonds between the alumina, silica, and hydroxyls break and the clay reforms into ceramic of just alumina and silica oxides and the hydroxyls are released, forming into more free water. This water is already gaseous so you won't have a steam explosion as before, but the water vapor must get out. The ceramic body will have open pores at the lower end of the temperature range for this phenomena, and the vapor will escape without harm. However, if the piece is very thick, there will be a significant temperature differential between the surface and the deepest interior, and the pores on the hotter surface will begin to close, sealing the escape route for the newly formed water from the interior. The result will be a spalling of the surface of the ceramic. Large chunks of the surface will just break off. The only way to avoid this is a very long firing with a very slow rate of temperature increase.

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I like your #3 option of slipcasting but not leaving it solid, then firing on coils, waster piece and/or grog. I think you will have less chance of warping with slipcasting than using slabs or hollowing out a form. If is has to be solid looking then maybe you could add a base to a slip cast piece after it has been removed from the mold.

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Test a batch of clay with 75-80% grog, then use a slip or glaze on the outside. This is the only way I could imagine you doing a "solid" block. Otherwise take the routes others have given you of cutting and hollowing, or slab building with thick slabs. Wooden forms would definitely help with the second technique in case you decided to use slabs.

 

 

best,

Pres

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My design approach for a solid block approach would be one or both of the two options:

Option 1.  Make the piece out of paper clay using dried 'blocks' of paper clay and paper clay 'mortar' to assemble the blocks.  After this was dried and bisqued, I would add a thin layer of paper clay and thinner layer of slip to produce a smooth surface layer.

 

Option 2.  Use the one of the clay bodies designed by Jerry Rothman or Fred Olsen that they used for their big sculptures.  These clay bodies have very little shrinkage and their pieces are also thick.  Rothman's clay was available from Aardvark several years ago.  If you called Fred Olsen, I am sure he would give you some advice on the clay body choices. 

 

More generally re the project:

Approach the problem by continuing to ask the kinds of questions you are doing, just go deeper into the requirements that the clay body (really the ceramic materials) must meet for final piece to be successful. 

 

From what has been revealed so far, I think you need a clay body that is solid, but possibly porous, that is dimensionally stable, dries uniformly in a reasonably short time, fires in a reasonably short time.  Does product need to be fully vitrified?   Think brick clay instead of tea cup porcelain.  Does it need to fired at all?  What about surface treatments?  Glaze, stain, paint, color, texture, gloss, etc.?

 

Could the project be made by making thin fired layers that are 'glued' together to produce the overall shape?  I once made a ceramic sphere that way.

 

LT

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Hello there,

First, thank you all for your time and support, I've found great tips reading your answers. Indeed, some market clay descriptions confirms that I should start with a clay with grog—like some of you've mentioned above, being use depending of the grog size in building medium/big pieces; could be a proper choice in this case.

 

@Marcia thanks, but I guess that will not be so sharp edge, building / cutting for craving will end up with a wobbling-looking piece.

@Dick White, a great ceramic chemistry lesson, I appreciate it!

@Min, Giselle I'll do some tests for sure using slipcasting.

@Mark, Chilly, wood/ concrete? â€”that's the challenge, to build these pieces using ceramic or a similar looking/feeling material. 

@Pres, Magnolia, indeed, as I've mentioned above using a clay with grog sounds good enough. Option 1 Mag, using paperclay also sounds good, and this will fit better for fine detail pieces, I guess.

 

To answer your questions Mag:

I think you need a clay body that is solid, but possibly porous, that is dimensionally stable, dries uniformly in a reasonably short time, fires in a reasonably short time.  â€”Very true.

 

Does product need to be fully vitrified? Does it need to fired at all? —It will be preferably to be fired up to 1150-1300*C after the biscuit firing but as far as I can see, grogged clay is low fired (1050-1080*C) at least on some producer pages.

 

Think brick clay instead of tea cup porcelain. —Sounds great! a good alternative, I'll search for that. 

 

What about surface treatments?  Glaze, stain, paint, color, texture, gloss, etc.? —Texture could be raw or if this will be possible, although I'm not so sure taking in consideration the material consistency, I'll try to use diamond papersand smoothing the surface.

 

Using pieces is not really my intention because I suppose that the gaps will be visible, I am looking for a seamless surface texture.

Anyway, now comes the "best part" because the clay market is not so generous here and the shipping price will be 10x the product price. Hope to find some materials.

 

PS: I am out of likes until next day, All the answers will receive one because are good enough for me, thanks again.

 

 

 

 

 

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I am interested in combining ceramics with architectural models (I'm not the first, there are plenty of examples) not in deepest details but following a predefined shape. Could be somewhere between architectural-model-deco-art. 

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