Why my clay acts like this?

[glazenerd]

Hi Tina:

Been following, going through the information you posted. Sand additions are called "temper" in our clay world: first used in native pottery, and later by the brick industry to make clay more suitable for pressing. While sand added to the problem; it is not the problem. You soaked your clay for several days and still had lumps: this indicates the real problem- it is called "cementing." Cementing is a severe form of flocculation; caused by high iron/alumina levels that create a strong positive charge in the clay which makes it resistant to uniform dispersion of particles: which in turn results in delamination, sheering, and cracking. It requires more than adding plasticizers to the clay: you have to break the strong positive charge that creates this problem. Acidity creates flocculation and alkalinity creates deflocculation.

Now lets put that theorem to the test: 1. Find two 1" hard clumps of clay. 2. Fill 2 glasses, bowls, dishes with a 1/2 cup of tap water. 3. Add 1/8 teaspoon of sodum or potassium feldspar to just one  glass (leave the other plain tap water). If you do not have feldpsar; then add 1/8 teaspoon of baking soda.  Stir it well to disperse the powder. 4. Drop one chunk of clay into each glass/bowl. (Do not stir or agitate.) Let it stand for 30 minutes. 5. Use your finger or spoon to see if the clay chunk has dissolved on its own.

If my theorem is correct: then the chunk of clay in the glass with the feldspar/baking soda will have dissolved on its own.  Feldspars/ baking soda create alkalinity; which in turn creates a negative charge in the water; which in turn neutralizes the positive charge that created the "cementing" property.

Tom

Edited October 29, 2022 by glazenerd
typo

[oldlady]

tina, do not buy the Keraplast.   it is not a clay you can fire to make it into pottery.    it is just for making pretty things to sit around and be looked at.  it will never hold water so cannot be used that way.   it is extremely expensive, too.

you are correct, peter h and hulk are awesome.   they are able to research on their computers to find just about anything.

please check the white studio, hulk lists, i do not know where it is or if it is close to you.   peter's map shows many town names, where is the nearest one to where you live?

i congratulate you also on your skills with the english language.   to search so hard for something you do not truly understand and have to do it in a second language is impressive.

[Kelly in AK]

There is clay suitable for pottery probably not too far from where you live (“a small town in the southern part of the country”). Do not be dissuaded, do not be discouraged. It is clear through your posts you have made great efforts to understand the process of making pots. It is also clear you have learned a great deal, you are ahead of where you were. From what I see Georgia has a ceramic tradition. I want to encourage you to explore it any way you can. 

https://georgiatoday.ge/the-history-of-georgian-ceramics-one-of-georgias-oldest-traditions-still-very-much-alive-today/

https://wander-lush.org/georgian-pottery-ceramics/

[JimLurking]

18 hours ago, glazenerd said:

Hi Tina:

Been following, going through the information you posted. Sand additions are called "temper" in our clay world: first used in native pottery, and later by the brick industry to make clay more suitable for pressing. While sand added to the problem; it is not the problem. You soaked your clay for several days and still had lumps: this indicates the real problem- it is called "cementing." Cementing is a severe form of flocculation; caused by high iron/alumina levels that create a strong positive charge in the clay which makes it resistant to uniform dispersion of particles: which in turn results in delamination, sheering, and cracking. It requires more than adding plasticizers to the clay: you have to break the strong positive charge that creates this problem. Acidity creates flocculation and alkalinity creates deflocculation.

Now lets put that theorem to the test: 1. Find two 1" hard clumps of clay. 2. Fill 2 glasses, bowls, dishes with a 1/2 cup of tap water. 3. Add 1/8 teaspoon of sodum or potassium feldspar to just one  glass (leave the other plain tap water). If you do not have feldpsar; then add 1/8 teaspoon of baking soda.  Stir it well to disperse the powder. 4. Drop one chunk of clay into each glass/bowl. (Do not stir or agitate.) Let it stand for 30 minutes. 5. Use your finger or spoon to see if the clay chunk has dissolved on its own.

If my theorem is correct: then the chunk of clay in the glass with the feldspar/baking soda will have dissolved on its own.  Feldspars/ baking soda create alkalinity; which in turn creates a negative charge in the water; which in turn neutralizes the positive charge that created the "cementing" property.

Tom

This 'cementing' reminds me of the more common 'hard-panning'?

And in other parts of the world temper = grog?

The Canadian Tony Hansen has lots to say about grog but nothing about temper. Glazy doesn't help much either.

[PeterH]

Maybe of interest ...
Temper (pottery) https://en.wikipedia.org/wiki/Temper_(pottery)
A temper is a non-plastic material added to clay to prevent shrinkage and cracking during drying and firing of vessels made from the clay.
... and goes on to list 12 types

I don't know how useful this definition is, or how widely it would be accepted.

Note that the definition doesn't cover the use of  "combustibles" such as coffee grounds or expanded perlite to add texture to the fired surface.

Are there any additions to a flameware body purely to modify the fired thermal properties, rather than the shrinkage/cracking of the body during drying and firing? [Mica might be one?]

 

PS It doesn't pass modern  health & safety requirements -- and it has nothing to do with your questions -- but have you heard of  Obvara Raku? Which I believe has it's origins in sealing porous cooking vessels.

Marcia Selsor's Tips on Obvara Firing
https://ceramicartsnetwork.org/daily/article/Marcia-Selsors-Tips-on-Obvara-Firing
The obvara firing technique is a technique originally used to seal low fire pottery. It is believed to have originated in Eastern Europe during the Middle Ages.
 

 

 

 

 

[Callie Beller Diesel]

@JimLurkinghi and welcome!

To add to what Peter said about terminology, all grog is temper, but not all temper is grog. Grog is clay that’s been fired and then ground into assorted sizes of grit. It can be added to clay bodies, or its used “off label” to large pieces on in the kiln to prevent cracking/warping/glaze getting onto shelves. North Americans tend to refer to the specific temper they’re using by name, whether it’s sawdust, paper pulp, chicken grit, decomposed granite, sand, etc. 

Temper is a term I’ve seen used more frequently in British or European references, or in archeological/art history writing. In those contexts, it’s a broad category that could mean anything from straw in adobe to river sand in assorted primitive firings, to chamotte, which is French grog from a specific clay.

 

(I will not make sparkling clay jokes, I will not make sparkling clay jokes, I will not make sparkling clay jokes)

[glazenerd]

Tim:

Temper is well known among those who collect and process natural clay; and those who fire primitive pottery. Temper is added for malleability; in lieu of known clay formulation methods. Grog is added to increase green or fired strength, or it can be added to control warping, and or increase thermal shock properties.  Hardpanning is more associated with glaze than clay; although it can happen in soil deposits if conditions are right. Processing natural clay rarely comes up on this forum: although it has gained popularity in the last decade. 

Tom

[suetectic]

On 10/31/2022 at 6:58 AM, glazenerd said:

Tim:

Temper is well known among those who collect and process natural clay; and those who fire primitive pottery. Temper is added for malleability; in lieu of known clay formulation methods. Grog is added to increase green or fired strength, or it can be added to control warping, and or increase thermal shock properties.  Hardpanning is more associated with glaze than clay; although it can happen in soil deposits if conditions are right. Processing natural clay rarely comes up on this forum: although it has gained popularity in the last decade. 

Tom

I'm unsure what malleability means outside of degrees of plasticity.

I'm wondering too further regarding.

On 10/30/2022 at 9:14 AM, Callie Beller Diesel said:

all grog is temper, but not all temper is grog

I'm curious as well what an example of temper not grog is.

I'm better with tldr versions so please forgive me if I'm trying to over simplify. I'm continually trying to uncomplicate my understanding of things.

I'm wondering how much clay particle charges go into flocculating or deflocculating glaze slurries or if there is a more important mechanism working.

So many threads to hijack.

as an edit I was searching something unrelated exactly but found a post "The locals added fiber from cat tails or cat tail fuzz to make handles. They wedged it in.  It worked.  It help bind the clay. It was an earthenware."

Can this then be temper? as it improves the malleability but is not grog?

Edited November 2, 2022 by suetectic

[PeterH]

19 minutes ago, suetectic said:

I'm curious as well what an example of temper not grog is.

This gave 12 examples of types of temper, only one of which is grog.
Temper (pottery) https://en.wikipedia.org/wiki/Temper_(pottery)

[suetectic]

32 minutes ago, PeterH said:

This gave 12 examples of types of temper, only one of which is grog.
Temper (pottery) https://en.wikipedia.org/wiki/Temper_(pottery)

Whoops thank you for pointing out the wiki already posted.

So now I wonder if the 'grit, sandstone, limestone, igneous rock' are considered temper because they are not 'tempered'?

Referring to "Some clays used to make pottery do not require the addition of tempers. Pure kaolin clay does not require tempering.^[5] Some clays are self-tempered, that is, naturally contain enough mica, sand, or sponge spicules that they do not require additional tempering"

Florida looks like a good place to study 'tempering' in ceramics. In particular the archaeology department at the University of Florida.

Edited November 2, 2022 by suetectic

[PeterH]

15 minutes ago, suetectic said:

So now I wonder if the 'grit, sandstone, limestone, igneous rock' are considered temper because they are not 'tempered'?

Not the way I read it, I think it's the clay/body that is tempered.

https://dictionary.cambridge.org/dictionary/english/tempered
tempered (adjective): limited or controlled, or made less extreme.

So you achieve  a tempered clay by adding temper to a less manageable one.

From Hamer & Hamer
Temper. An addition to clay which improves work-ability, e.g. sand and grog. Temper will also affect the fired result but it's introduction is essentially to assist forming and uniform drying.

 

 

[suetectic]

43 minutes ago, PeterH said:

Not the way I read it, I think it's the clay/body that is tempered.

https://dictionary.cambridge.org/dictionary/english/tempered
tempered (adjective): limited or controlled, or made less extreme.

So you achieve  a tempered clay by adding temper to a less manageable one.

From Hamer & Hamer
Temper. An addition to clay which improves work-ability, e.g. sand and grog. Temper will also affect the fired result but it's introduction is essentially to assist forming and uniform drying.

 

 

This helps.

So maybe only clay and refractories can be grog and temper includes organic or non-refractory material?

Edited November 2, 2022 by suetectic

[Callie Beller Diesel]

@suetectic grog is one thing: fired ceramic that’s been ground up to a sand like consistency. Temper is lots of things that can get added to a clay body to adjust it.

[suetectic]

1 hour ago, Callie Beller Diesel said:

@suetectic grog is one thing: fired ceramic that’s been ground up to a sand like consistency. Temper is lots of things that can get added to a clay body to adjust it.

so mullite(from kaolin) is a grog while kyanite is a temper? nvm both are ultimately derived from kaolin if I understand correctly so both can be grog if ceramic includes kaolin.

I want to be able to explain this in simple terms in possible.

I should have probably suggested previously that temper 'also' includes to help indicate temper includes refractory and non-refractory material.

Edited November 2, 2022 by suetectic

[Min]

41 minutes ago, suetectic said:

I should have probably suggested previously that temper 'also' includes to help indicate temper includes refractory and non-refractory material.

I would suggest that the definition of temper would also include organic and inorganic materials. Grog could be further defined as to being soft grog (not vitrified) vs vitrified. Also whether the word temper is used as a noun or a verb.

[Babs]

4 hours ago, suetectic said:

so mullite(from kaolin) is a grog while kyanite is a temper? nvm both are ultimately derived from kaolin if I understand correctly so both can be grog if ceramic includes kaolin.

I want to be able to explain this in simple terms in possible.

I should have probably suggested previously that temper 'also' includes to help indicate temper includes refractory and non-refractory material.

You are overthinking this I feel.

you have a clay body .

It is not the best to work with.

You add a temper to it, or temper it by

adding the substance of your choice, or want to test,.

this substance is the temper which can be a grog or any other substance you find helps you to work with the clay body.

Ceramics is difficult enough without getting bogged down in the semantics imo.

[Tina01]

On 10/29/2022 at 8:00 PM, glazenerd said:

You soaked your clay for several days and still had lumps: this indicates the real problem- it is called "cementing." Cementing is a severe form of flocculation; caused by high iron/alumina levels that create a strong positive charge in the clay which makes it resistant to uniform dispersion of particles: which in turn results in delamination, sheering, and cracking. It requires more than adding plasticizers to the clay: you have to break the strong positive charge that creates this problem. Acidity creates flocculation and alkalinity creates deflocculation.

I did try the experiment, with a lump of clay that was still not dissolved. added 1 teaspoon of baking soda in water then added the clay, it started to break:

however after half an hour:

then waited one more hour, but even after stirring there were some smaller lumps:

and they're there now after 4~5 hours.

 

so I  repeated the process with dried pieces (they were not lumps, but pieces of my recent failure project) . Again added 1 teaspoon baking soda to one container stirred well and added the parts, left one is just water:

after 15 minutes:

after 1 hour, water only:

with baking soda:

after that, I stirred both and let them sink:

I didn't  notice a difference in particle size between the two while stirring and in first experiment I could achieve the same result using a mixer (for dissolving the lumps, not the cementing , if that was the problem).

So, did it help? I can't judge,  and let's say it did, what should I do next? adding baking soda to the dry clay powder? 

[Tina01]

Another failed attempt:

cracks in drying time although I made my best efforts, wrapping it in two layers of thick towels. and it shrinked but there where still plenty of space if it wanted to shrink even more and not crack.

[Tina01]

I finally found a semi-trustable source for clay unfortunately it's a  one hour drive there, so I just bought ~20lbs of dry clay powder and 4lbs of bentonite clay, to see how it works. interestingly they have about the same volume. And oddly the clay is slightly greenish in color, anyone knows what it means? 

the bentonite one has a peculiar odor to it, is it normal? when wetting grows even larger in volume (maybe 3~4 times). in very smal quantities dries to a likely thin transparent fragile sheet of plastic.

made a tile for shrinking ratio, and roughly it's 5% (went from 10cm to 9.5cm):

didn't dare to mix bentonite with it, as I guessed the plasticity is fine enough:

then the problem that I always have was present again:

rolling the slab (6mm thickness):

but the back side:

if I smooth either side, the other looks like above. 

to reduce this I've wetted the board, it helps, but not enough. 

should I add bentonite clay to it? I guess about 2% right? or does it need more water, wedging, or aging (letting the wet clay sit for a week)? 

In addition to above, it might need some grog also (crushed breaks in 40 mesh)? I found these on digitalfire.com , 40 comes from size of sugar so I have something to compare with. 

Edited November 2, 2022 by Tina01

[glazenerd]

Hi Tina:

Lets skip down to the pictures where you drop in the squares of your clay. "pieces of your failed attempt."  Notice on the right (with baking soda) the clay begins to dissolve as soon as it hits the water. In the next picture: the plain water (left) is partially dissolved, but not fully dispersed. On the right (baking soda), the piece is fully dissolved, AND fully dispersed. The next pic ( 1 hour, water only) the clay is still not fully dispersed, and there is cording present. (cording means visible lines of color and distinct lines in the clay). 4th pic (one hour with baking soda) the clay is completely dispersed, no cording. 5th picture ( I stirred both and let them sink). the left has completely separated between material and water. The right has separated into three layers; each layer being (large particles on bottom, medium particles center, and fine particles on top (looks like colored water).

After reviewing: you have three points. The cementing problem is medium; I have seen worse. 2. The clay lacks any naturally occurring feldspar ( sodium, potassium, nor any calcium) 3. The particle distribution is mostly larger.

Lets see how to word this without being too techie. Feldspar ( sodium and potassium) along with calcium create a negative charge in the clay/ and water. When that negative charge is absent; clay forms clumps even when wet (flocculation, and when severe- cementing). Feldspars are alkaline, and alkalinity creates a negative charge; which repels adjoining particles; or what potters call plasticity. Plasticity is a function of deflocculation. That same negative charge ( or lack thereof) also plays a role in drying. A strong positive charge ( your clay currently) will add to cracking when it dries; which is further compounded by larger clay particles. So to correct it; you have to create alkalinity ( which is done by adding feldspar or calcium), and by the addition of fine particle clay.  You have bentonite now: do you have access to feldspar?  sodium, potassium, or calcium?

Take a pint of water, and add 1/4 cup of baking soda (stir well). Add 8-10 pieces of your "failed experiment clay chunks"; and let them dissolve completely ( about an hour). Stir it well, then add 2 tablespoons of bentonite ( little at a time, stir between each addition). Let it sit overnight, and pour off any excess water that comes to the top. Empty it out on a board or table (something flat) and spread it out. Let it dry down to a "clay consistency".  Then just roll it out as a flat slab and let it dry. All we are checking is cracking- nothing more.

Tom

 

Edited November 2, 2022 by glazenerd
typo

[Tina01]

2 hours ago, glazenerd said:

You have bentonite now: do you have access to feldspar?  sodium, potassium, or calcium?

unfortunately not, for calcium I can ground some seashells?  but still I'm not even sure that it's really bentonite, wrote its properties but nobody has confirmed yet. 

I was blamed for adding unwashed beach sand but shouldn't it contain (or contaminated with) calcium and/or sodium perhaps? 

2 hours ago, glazenerd said:

then add 2 tablespoons of bentonite

isn't that too much? would be much more than clay itself in volume!

Thank you,  will try that.

Edited November 3, 2022 by Tina01

[Min]

On 10/29/2022 at 8:26 AM, Hulk said:

Isn't Georgia known for white clay?
Perhaps pottery shops in Georgia could direct you to suppliers.

Some may carry supplies! For example, the MODI Ceramic Project in Tbilisi, who feature Seramiksir products
MODI ceramic shop

This shop's website mentions Georgian white clay, " The business prides itself on being the first studio to develop and produce the acclaimed Georgian porcelain..."
About us – White Studio
 

Here's a listing of global suppliers, interesting!
Ceramic Materials Suppliers — pottery to the people

I found a  potter in Georgia that might be able to help if Tina is looking for a Georgian contact, perhaps this fellow could help with where he gets his clay or materials from:  https://www.homofaber.com/en/discover/discover-gigisha-pachkoria# . 

[glazenerd]

Tina:

greenish clay typically indicates calcium and/or magnesium is present. In some cases; calcium/ iron. Bentonite can absorb 15 times its weight in water: so it will swell when water is added.   Yes, the formula I gave you is very rich in plasticizers; I did so with intent.  Note: when you post pics: number them, so the discussion is easier to follow. Also, do not throw away this test batch regardless of outcome. I plan on reusing it.

The weird smell may be organics.

Tom

[Tina01]

21 hours ago, Min said:

I found a  potter in Georgia that might be able to help if Tina is looking for a Georgian contact, perhaps this fellow could help with where he gets his clay or materials from:  https://www.homofaber.com/en/discover/discover-gigisha-pachkoria# . 

Thank you so much! this was a great favor, I'll contact him for sure if needed. but from my past experience in arts, generally speaking it's more likely to get scientific answers from the internet, that is most "masters" try to dictate what they have learned and never doubt on their teachings, whether there might be better and more correct approaches available. 

Again, thank you, your time and effort are greatly appreciated.  

[Kelly in AK]

I apologize for stepping backward a few comments, and am repeating what’s already been said in some ways, but I want to help clarify the language.

To “temper” something is to make it useful/manageable. Tempering steel makes it useful for knives, tempering clay makes it useful for pottery. The term “tempera paint” comes from this use of the word, tempered pigments.

Concerning pottery, the most frequent place I’ve seen the word “temper” used is from people interested in the archaeology of clay. People more on the making side of things tend to describe specific materials (e.g. sand, grog, molochite, etc.). 

Edited November 3, 2022 by Kelly in AK
Clarity