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LeeU

Clay for slab building

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My current project is making herb markers for retail sale. The basic form is like a paint stirring stick with a point at the end (no indent at the top). Greenware is about  9" x 1" x 1/8". The pic is not the final design--I'm not running the stamp to the top, for example and the point will be a bit longer/pointier. I'm still perfecting my technique for a retail production process-it is quite the opposite of my usual headspace when working w/clay (I'm very rough & tumble/freeform/warts & all). While I am doing this mental (& physical touch) reset to get into a mode of more precision & refinement, I have learned that the clay I am using is not suitable--way, way too moist/soft/sticky. In the past I have used Bella's Blend, a supposedly "true" low-to-mid fire body at 05/5 with great results, tho I personally favor stiff clays w/grog. I am looking for some suggestions, based on experience, regarding a body (any supplier-I'll pay the shipping!) that might be especially suited to making this form. I think I want to go low fire using Mayco Stroke & Coat, IF it is likely the sticks will be strong enough to stick in a planter outdoors (thoughts?). If not, I'll do 5-6. I really-really-really want to do single fire. Someone would have to convince me if that's a bad idea and give me a good reason why! Thanks in advance-I am experiencing way too much breakage with the current clay. 

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It looks like the clay is working well for detail.  Maybe it just needs a little time on a plaster slab to set up a little.  Moisture content from suppliers is not consistent, so better get used to that.

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Single fire shout out. You won't find me trying to convince you that's a bad idea!

If the end user keeps them outdoors through winter, they may freeze crack. However, if you were to fire them upside down in a holder like cones, you can glaze the entire inserted part, which can negate a lot of moisture uptake, leaving only the top susceptible to water, which can also give a good rough place to grip them for removal.

It does seem a simple enough shape to accomplish with any clay.

What kind of breakage? 

What's your process?

Sorce

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I don’t have a claybody recommendation. But when I make coasters,. I roll out the slab at the beginning of my work day, then come back 3 or 4 hours later to make the coasters. A few hours of drying will remove the sticky/mushy factor from most clays. The amount of time is individual, depends on your climate. 

And I think a low-fire single firing will work. 

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On 7/30/2020 at 10:01 AM, Sorcery said:

fire them upside down in a holder like cones, you can glaze the entire inserted part,

What do you mean a holder like ones? I was firing them flat, glazed on one side. Please describe this holder--and are we talking about glazing just one side or both, in terms of overwintering strength (I'm in New Hampshire & most of my customers are in NE. We freeze hard & long up here).   The breakage is the stake snapping in half when I look at it cross-eyed! Has even happened during drying when not touched after being set on the drywall. My process is to roll (table top Bailey) & rib-compress a slab, set up a row of paint sticks, cut the tops in a line across the sticks and then down each side of each stick. Gives me perfect sizing.  I don't have my metal v-shape yet to make the points (like a cookie cutter for the tips) but I am cutting the points just fine. If any slight smoothing on any given edge is needed, I do it gently with a tiny piece of damp chamois. I let them firm up a bit and then carefully move them from the slab mat to the drywall (I use a large thin pizza-peel-like spatula,  slid under the whole line and onto the board in one motion and don't touch until dry and ready to glaze.  They dry under a thin dry cleaner bag w/a tile on top to weight them flat. I remove the tile once they are past the stage where they could still warp. SO far so good, with that.

And Mea,  I am working hard to maintain the patience to walk away and let the clay firm up  before cutting/stamping (I am impossible sometimes-talk about shooting oneself in one's foot-I do know better, but no, gotta jump on everything right away). I'll probably switch to a stiffer clay regardless-this is clearly not the right body for this form. ..probably terrific for throwing. Thanks.

Edited by LeeU

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12 hours ago, LeeU said:

They dry under a thin dry cleaner bag w/a tile on top to weight them flat. I

This must be ware...get it...ware....the breakage occurs. 

I exclusively slab build, with at least fine grog or sand clay.

Working on Hardie backer, I rib in all four directions, flip, rib all four directions, flip, and realest this till leather hard. This ensures nothing warps. Porcelain takes more flips than an open groggy clay, and also needs more ribbing, so any clay is ready when it is ready kinda automatically.

Using this method with your clay should ensure no warpage, and no need for the tile atop.

I'll draw you a pic of the holder an firing I'm imagining. Later. Apologies.

 

Sorce

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This white clay is Amaco 46. Which is my grog free clay. Ribbed as such, only this one, which was likely thrown on an unflat surface after discard was slightly warped. 

No topper needed. 

Only 3 to four good even layers of "molecule packing". The "memory remover", or "maker" as it were.

 

Running out. Let's chat!

 

Sorce

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lee, why the plastic?  that thickness should not have a problem drying between drywall sheets overnight.   are you cutting the clay from a new bag of clay without wedging, slamming it onto something sturdy like a concrete patio block (if nothing better)before rolling?  

if you would like a pair of printers blankets, just ask.    roberta uses the same roller, i think and she likes hers.

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Though some folks have succes drying between layers of things, It is actually uneccesary, and as we are witnessing, actually highly detrimental, depending on the clay, and prior treatment of it.

Just ONE extra swipe of the rib on one side is enough for some clays to want to bow. Any minor amount of bowing trained into the molecules IS garaunteed to break if that bowing has nowhere to go.  Hence the breakage in this project.

Most of the shrink occurs by leather hard, shrink is what makes things bow, by ribbing and flipping until leather hard, we completely eliminate the need to "keep things flat".  No shrink no bow.

Add in the "pinning and shrinking", which is essentially the same phenomenon as "s" cracks, and it's quite easy to see why near every piece is cracking.

But screw speculating failure.

I am absolutely positive all you have to do to find success...is...

Make a slab correctly, rotating and flipping between about 60 and 80% evenly.

Then Rib perfectly evenly. Depending on slab size, x amount of strokes in your most comfortable position (usually towards you) then spin the slab and do all 4 directions. Sandwich and Flip and do all 4 directions. Note, spin the slab, because you can't apply the same pressure with an away stroke as a towed stroke. This is a requirement of perfect. Spinning on a wide banding wheel works.

After a couple flips the clay should no longer stick to the Flipboard at all. One more ribbing for good measure. 

You may decide to outline your cuts and texturize here, to minimize texturing failures that can occur with thin strips.

Then cut out your strips. Some clays may require a downward full sheer cut to not introduce warp again. Dragging a knife down one side reorganizes those side molecules again, which can then warp during firing.

These can be left in the wide open to continue drying. 

If you, @LeeU can't get near 100% success with this method, I will buy you a box of clay.

Sorce

 

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Thanks for all the info--I already do just about everything mentioned--have for years--incl. printers blankets/proper ribbing technique etc.  I have never had this problem until this bag of clay.  I like the technique suggested of applying the stamp & vine to "outlined" stakes on the large slab on and then cutting them using a full shear cut---I'll try it.  I like the drywall for my humid space, so now I have enough for top/bottom.  Anyway, it seems like "problem solved". I  switched to T3  and have not had a single crack/warp since. 

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