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Clay Has Memory - Applied To Wheel Thrown Forms


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i think i have a basic understanding of what clay has memory means. i definitely have a better understanding of it with hand building (if you only roll the clay slab in one direction and try to form something in another direction there is a possibility that it might warp).

 

when does it develop its memory? when you stop playing with it and leave it alone? how does it apply to wheel throwing?

 

i understand the statement but dont know how to apply it in wheel throwing (in my world that means i dont really get it). 

 

i would like to use the principle to my advantage. in my voracious readings i read somewhere of how to utilize this while making plates, but alas i didnt write it down.

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One of the easiest things to notice in the way of memory is a thrown teapot spout that has been cut at an angle to match the top rim of the teapot. If the wheel is going in a counter-clockwise manner, the spout will when fired-unwind slightly in a clockwise motion, there for the angle of the cut needs to be slightly to the right 3-5 degrees for the cut to be parallel with the rim.

 

Other instance of this would be a bowl that has been thrown thinly, and later when cheese hard gets warped lightly. When fired it comes out the way it had been originally. 

 

Instance of this memory are something that as you work with the clay, and notice changes is firing, and evaluate those changes that you are able to make conclusions about memory, firing cycles, assembly techniques and other things about the clay. A lot of what we do out there is intuition, and without apparent thought even though years ago we had an AHA moment that became innate and basically a priori knowledge that we act on without thinking.

 

 

 

 

best,

Pres

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One of the easiest things to notice in the way of memory is a thrown teapot spout that has been cut at an angle to match the top rim of the teapot. If the wheel is going in a counter-clockwise manner, the spout will when fired-unwind slightly in a clockwise motion, there for the angle of the cut needs to be slightly to the right 3-5 degrees for the cut to be parallel with the rim.

 

Other instance of this would be a bowl that has been thrown thinly, and later when cheese hard gets warped lightly. When fired it comes out the way it had been originally. 

 

Instance of this memory are something that as you work with the clay, and notice changes is firing, and evaluate those changes that you are able to make conclusions about memory, firing cycles, assembly techniques and other things about the clay. A lot of what we do out there is intuition, and without apparent thought even though years ago we had an AHA moment that became innate and basically a priori knowledge that we act on without thinking.

 

 

 

 

best,

Pres

 

Actually, the spout continues to twist in the direction of the torque, clockwise as you look into the spout.

 

Memory is not an issue for most wheel thrown forms, mostly just for those long narrow things like spouts. It has to do with the alignment of the clay platelets. You can trim the outside of a pot totally smooth, then the throwing rings come back after firing because the pressure of your fingers aligns the platelets in a certain way during throwing. So you have to smooth the pot during throwing rather than trimming it smooth.

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I make square bowls

Here is how clay has memory in a thrown form.

I throw say a 1.5# cereal bowl-round-let dry to trim state 

Trim a foot and rewet with sprayer-paddle it square

This is common form for me.

In the glaze fire  the square bowl tries to go round again-just a bit-its like it knows where it was at one time and is trying to get back there .

The more square the bowl is the less it can go back round.I make this square bowls in regular and chopstick bowls with a fee notches in the rims for holding high quality chopsticks -I bought a few cases of square sticks a few decades ago with gold bands.Almost out now-so much for a lifetime supply idea.

As to teapot spouts that an easy one as its written on my wall in shop they always (if you throw on a standard direction wheel) will unwind in a clockwise manner looking at the spout as stated above.

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As to teapot spouts that an easy one as its written on my wall in shop they always (if you throw on a standard direction wheel) will unwind in a clockwise manner looking at the spout as stated above.

 

They don't unwind. They continue to wind. Look down at the wheel and image you're holding onto the tip of the spout with the wheel turning. That's the direction of the torque, and they continue to turn that way when fired. So it's not really memory in that it goes back, it's memory in that in remembers which way to twist.

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OK, got me, poor example there :wacko: . How about the bowl example? :huh:

 

 

best,

Pres

 

I don't think you're necessarily wrong about that being memory. I think the same phenomenon is in effect either way. Whether in a narrow spout or a wide bowl or rolling a slab, the platelets are being aligned in a certain way during the making, and during firing they tighten up. In the case of a narrow spout it causes twisting, which probably happens in all thrown forms to some degree, it's just not noticeable in a wider piece, nor is it very noticeable in a spout that hasn't had the lip cut at an angle. In a bowl or slab that has been altered, as they tighten up they try pull the shape back to the original configuration. When you alter a piece, the platelets are no longer aligned in a way that agrees with the form. In the case of a squared bowl, they platelets were aligned to make that specific round form, not a square form. I tend to think of it as returning to a state of equilibrium, where the particles are happy, kind of like a slinky returning to its closed position.

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Pictures of clay alignment, 2 clays thrown then cross section shots. First one shows how the clay is aligned after coning, second with no coning. (yup, I know good wedging would do the same thing) The article the pictures are from is written about S cracks but the pictures show alignment well.

0310-ppp-feat3-fig6a.jpg  0310-ppp-feat3-fig6b.jpg

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I tend to think of it as returning to a state of equilibrium, where the particles are happy, kind of like a slinky returning to its closed position.

 

OK I understood that one sentence and I know what platelets are. :ph34r:

 

Is there a way for me to control warping due to memory in say, large hand-built bowls or platters? Like in the original post I can sense them trying to achieve some semblance of a former shape even when I roll out a slab, but was not aware this continued into drying and firing.

 

Is there a simple way to counteract this? Do some clays warp more than others?

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Yes, some clays warp more than others. Definitely. To reduce warpage, roll your slab in several directions when you make it. Also go over it with a rib to compress the platelets after it's rolled out. I find that I need to do that anyway to get rid of the canvas marks. Compress the edges as you smooth them out during and after construction, to set the platelets into their final position.

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Yes, some clays warp more than others. 

Why? is it because of the chemical composition. so clay is different from dirt because of its plasticity. meaning is plasticity the main difference? what exactly gives the clay its plasticity? is plasticity a chemical composition or just finer material. does dirt have platelets too? dirt platelet? or is dirt on its way to become clay once it has been ground fine enough which might or might not happen. 

 

all kinds of rocks yield clay right? that's what gives it its colour. iceland has black clay - so that's metamorphic? and the colour is really about iron content.

 

sorry just thinking aloud.   

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 add 10% molochite. 

i just read about molochite on digital fire. is molochite another word for grog? that's what the description sounds like. 

 

is that what's used in sculpture clay which makes walls hold up better but not good for throwing? is that what i feel when i touch the clay. 

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Preeta  --- study grog verses grolleg.    Warning: long boring post ahead- flee--save yourself!!

 

Clay plasticity is an molecular electrostatic force called bond polarity. All elements have either an electropositive or electronegative charge: and these charges cause elements to bond (cling together) or repel each other. The simplest way to illustrate it is magnets: very large to very small magnets; with either positive or negative charges. it is common knowledge that if you put two negative ends of a magnet; they repel each other; or if you put the positive to the negative: they stick. That very simple principle also occurs on a molecular level.

 

Each ingredient in clay has a molecular electrostatic charge; which does not effect the other when they are dry. However, when water is added: those charges are transferred between each of them. No different than dropping a hair dryer into a tub of water: the electrical current is conducted into whatever else is in the tub. So the water is the conduit in the clay body that carries the electrostatic charges between ingredients: clay, silica, alumina, and feldspar. All clay, rather stoneware or porcelain are just varying amounts of alumina and silica: aluminosilicates. So you have to look at each ingredient as a magnet: as the atomic radius of each element decreases in size: the ionization energy increases: which causes the electronegativity to increase.   Big magnets to little magnets in easy terms.

 

Silica has an electronegativity value of 1.90 (big magnet) and sodium has a value of 0.93 (smaller magnet). So then you look at atomic radius: how big the molecule is: silica is a golf ball molecule, and sodium is a soft ball molecule. It is easier to strip an atom off a soft ball, and harder to strip an atom off a golf ball. Being easier to strip an atom makes it is much easier to melt: so that makes it a flux. Being much harder to strip makes it a transitional metal or metalloid. So the bigger the atom is: the easier it is to melt; but that also means a much lower electronegativity value (smaller magnets).

 

Now for the application of these terms-attributes.

 

Silica and alumina have much higher electronegative values than sodium or potassium (fluxes). All clay is alumina and silica: which have similar electron polarities: so they will bond (clump) in the presence of water. Mixing the two without a feldspar or a natural plasticizer ( ball clay, macaloid,bentonies, or hectorites) will just produce a grainy slurry that will dry into hardern chunks of cake. When you add the feldspar: the electronegativty (electron bond) changes:from a strong positive charge to a much weaker positive charge: so now the mixture begins to stick together to become the basics of a clay body. However, a clay body needs more than that to become plastic.

 

To become plastic, water has to be absorb onto the surface of the clay platelets. To accomplish that you either have to add an extra fine particle clays such as ball clay, macaloid, or hectorite; or a synthetic polymer such a V-gum T.  Any combination of these requires more water, and in addition absorb water onto the platelet much faster than a kaolin or fire clay. In addition, they also change the electrostatic charge of the entire mixture: allowing a greater molecular absorption of water. The exact mechanism means it has changed the higher electropositive charges of the clay into an electronegative charge: causing the platelets to repel each other. When  the clay platelets begin to repel (slide past each other instead of bonding to each other) you have plasticity. The higher the negative charge is; the more plastic it is.

 

Nerd

 

Edit: when you add sodium silicate to a slip you are seeing an change in electrostatic charges. The sodium creates a negative charge in the mixture; and the particles begin to repel each other (thinning). That reaction is short lived because the sodium mixture has a short reaction time.

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Nerd, so when we roll and flip and compress the clay platelets are we forcing them to align and thereby removing some of their plasticity?

 

Not a scientist but am fascinated by this subject and trying to picture in my head the why's and what's of it all.

 

T

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Well Pug: let me see if I can visualize this with words. Plasticity is created by electrostatic charges, and memory is cause by grain boundaries of the clay. There are some interrelated properties that effect both, and cause reactions in both. However, memory has more to do with particle sizes of the clay primarily, chemistry secondly, and finally electrostatic charges do play some role in memory.

 

As always, let me use everyday items to illustrate. Kaolin is like the size of rice, and ball clay is the size of table salt. (particle sizes) Obviously a cup of salt will naturally compact more than a cup of rice. However, salt is basically round so it will stack at random until the cup if full. Rice is elongated; it has a definite shape and will stack according to that shape. (grain boundaries). The elongated ends will stack because of its natural shape; instead of stacking randomly like salt. Now throw in the electrostatic charge: the ends of the grain of rice are positive; and the side are negative. So the natural shape of the rice, coupled with the electrostatic charge makes the rice stack along its natural elongated shape.

 

 

220px-CrystalGrain.jpg

The particles that are stacked against each other tightly represents a ball clay: very fine, round: so it naturally stacks tightly together. The other areas with open spaces are like kaolins: larger, elongated: so it has naturally occurring spaces between them. So when you slab roll a stoneware body (fire clay/ ball clay); there is little room to compress on a molecular level: so there is little tendency to return to its natural grain boundary. Porcelain is primarily kaolin (rice) which has a large grain boundary; which also means there is larger open spaces between the clay particles. When you slab roll porcelain: there is a compression of grain: which naturally wants to return to its original space. The water in the clay it what fills the open spaces; and that water has an electrostatic charge based on the composition of the elements that make up the clay body. That electrostatic charge also wants to repel the adjoining clay particles: furthering the tendency to repel the adjoining grain.

 

Plasticity and memory are from different attributes of the clay, and its accompanying chemistry. Plasticity is primarily based on electrostatic charges, and memory is determined more so by the grain size (boundaries) of the clay particles. Although electrostatic charges has some role because the clay particles want to repel each other. Plasticity and memory both change as the body dries: because the loss of water changes the chemistry. Water is the conduit that carries the electrostatic charges between elements: so as it disappears: so does the electrostatic polarity between particles. Water is what also fills the spaces between the salt (ball clay) and the rice (kaolin) that wants to push the grains of clay back to their natural state when pressure is applied. As the water disappears; the mechanical forces separating the clay particles also disappears: which means memory also disappears..

 

Although plasticity and memory are different functions: there are some shared attributes.

 

Nerd

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wow, even i understand this. :mellow:  thanks, nerd.  and i will continue to beat my clay slabs to death after smashing them onto the ground and rolling them. (no warping on the big ginko leaf mold fired to 04!  no warping on the brocade geranium either.) :)

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 Warning: long boring post ahead- flee--save yourself!!

 

thanks for your advice nerd. i took your advice and ran right into it gleefully. and really 'enjoyed' your reply. makes sense. i understood it. thanks to prof. z. i just need to think in terms of chemistry. 

 

it wasnt boring at all. quite the opposite. i tried talking about this with my proff today and he called me a nerd. 

 

will read up on grolleg - i vaguely remember that as an english kaolin. 

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Nerd, thank you thank you thank you! I am beginning to understand so much more when it comes to plasticity and memory! I've just been figuring it out by experience, if I do this that happens, if I do that this happens, etc.

 

Most of the students I encounter, even ones that have been doing this for years, have never heard of clay memory. I demonstrate how to use the slab roller and the first thing I always hear is, I never flip and rotate my slabs! Hmmm so I explain in a very basic way about clay memory.

 

I start out by making a scrambling knot motion with my hands, saying when you start out your clay is undisciplined just going wild and partying. Oh I should state I have found students like to know but also tend to remember better if I can explain things in a fun way. If later on I see them forget about memory I simply walk by and say, gee I wouldn't want to be living with that tray it's going to throw wild parties every time you leave. They look up grin sheepishly then rotate and flip their clay.

 

Next to further demonstrate I show them by drawing lines in a grid fashion on a rolled slab, saying you are trying to get your clay particles to line up with each other.... I had no clue about differing shapes or sizes of particles so that explanation helps me understand more. THANK YOU! I tell them, but if you only roll in one direction or on one side only those particles are aligned and the others will want to go back to the shape they were in, in essence a warped tray is trying to rip itself apart to return to a state it understands.

 

I also have them drop their slabs on a ware board on to the floor, to settle the clay, I do this with any clay I plan to use for a flattish item, Jewelry, Ornaments, plates, platters, cheese boards, etc. my thinking behind this is if I have been moving the clay slab around chances are I have at some point I bent it and by dropping it gravity is working to tell the clay to forget that little inadvertent bend and lay flat. Not sure if that IS what dropping the slab does but I know from my own pieces if I do this step things seem to be just a tad bit flatter when it's all said and done.

 

Again thank you so much I learn something new every week on this forum!

 

T

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Preeta said: i tried talking about this with my proff today and he called me a nerd.

Welcome to the American Society of Nerds. The only requirement for membership is reading (and enjoying) technical articles that bore people to tears.

 

 

I've actually had more college agricultural soil science than I have ceramic technical education. For some reason I'm still trying to get the two to gel, which logically, they should do, somehow...

Actually, they are directly related. A fair amount of our terms and knowledge comes from the soil sciences. Plasticity, elasticity (memory), deformation, hydrolysis, hydration, oxidation, reduction: even our terms for the amount of water comes from soil sciences. WOPL (water of plasticity) is a soil science term used to indicate the amount of water any given clay will hold without becoming saturated (slip). This one should be familiar to you:

Nerd

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Preeta said: i tried talking about this with my proff today and he called me a nerd.

Welcome to the American Society of Nerds. The only requirement for membership is reading (and enjoying) technical articles that bore people tears.

 

Preeta, I used to hear term nerd quite a bit as a teacher, I always told the kids picking on another kid about being nerd. "Wake up, look around you, who is making the money, and running the world right now. That computer you use everyday uses software originated by a nerd, the phone you use, envisioned by a nerd. . . so don't be dissing the nerds out there, become one!" Some listened, some did not.

 

As to clay particles, I think it is a subject that is often not taught in the schools, especially in HS and undergrad. I really haven't had a lot of formal ceramics training, maybe 6 total courses in my lifetime. Didn't hear anything about clay particles and alignment on my own. Only learned about them from reading Hamer? from cover to cover. Helped me with cracks, compression and other things. Still had problems with cracking off the hump for years, then took a commission for 2K small cups or vessels for a religious workshop called Filling your Vessel. Took me a year to do it. In early research as I had to beat the S cracking problem as I had sooo many cracked pieces in the first bisque, I Found a video of a Japanese potter throwing off the hump using a pancake then drawing it up to form the walls. He explained that the clay particles were flat in the pancake, and then drawing the pancake up into the form caused the particles to curve around the base instead of having a confused area at the base, and the bottom was much more compressed. Tried it, it worked, my understanding improved, and I finished the order after several months, but on time.

 

 

best,

Pres

 

 

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awww pres. the prof. was just joking and meaning it more as a compliment.

 

however i DID have a proff tell me to stop asking questions in class. give the others a chance. i used to give the others a chance to ask and when they didn't i'd ask. then a week later he apologized and asked me to ask questions again because it broke the ice. i always play devil's advocate too and i also ask for others who i know want to ask but are afraid to. i feel i have the advantage of having crossed my 40s where i lost my self consciousness and was no longer quiet and shy like them. so i feel i need to contribute and ask for the others. 

 

my daughter straight out calls me a stalker. the other day she shared her favorite rap song with me. i was blown away and in tears by the poetry and raw emotions in there. daughter really liked the song and listened to it often but didn't know anything else about the song. but i needed more. so i went and researched the band. because just hearing the words weren't enough for me. 'i just enjoy the song ma. i dont need to know all its history and stuff.' i find people's lives fascinating. every piece of art - whatever form it may be i find is a self portrait. so i always try to find their story. and i also realize what i find fascinating others may not. so i've learnt to keep my mouth shut or i come off as a know it all.

 

and you are right Pres. At the community college level only the basics are shared. that's the attitude of education there is. esp. in clay the proff has so many students that he does not have time to really talk to any one, one on one. yet other proffs have time to sit and chat and share. 

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