Why my clay acts like this?

[Tina01]

@Babs @Hulk @oldlady

@Min

@PeterH @JimLurking

@glazenerd

 Can you guys please check my last post about the new clay and kindly guide me? (the one that shows coil, test title, and problem with the flattening)?

TYSM.

p.s. if any other photo required (from dry clay, bentonite, board surface texture, etc...) I will happily provide. 

Edited November 4, 2022 by Tina01

[PeterH]

10 hours ago, Tina01 said:

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.  

I think you misunderstand the point @Min was making. The artist she named must get their clay from somewhere, and perhaps they can help you get in touch with a supplier/source of pottery-grade clay.

[suetectic]

On 11/2/2022 at 12:54 PM, Babs said:

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.

I agree completely and appreciate this opportunity to help clarify the term. If I can avoid unnecessary complications and confusing language I am able to better explain myself if need be.

I like to consider myself somewhat well read and have a nice collection of books and magazines but it's very possible I just haven't been paying attention.  In the decades I've been involved in ceramics the discussion has always been around grog. I'm not super educated from any official ceramics program and I also don't prospect for clay for any sort of structural work so this is a good lesson.

I better leave this thread be or start my own.

thanks OP!

[Min]

@suetectic, we do go off on tangents on the forum but at the risk of hijacking the initial thread its best to try to keep them short. Can't know in advance how off topic a thread will go but at this point it would be best to start a new thread with your temper definition question if it's going to go any further. thanks 

[Min]

@Tina01, I think you need to decide if you want to try and fix your current clay or try and find a new supplier who can sell you a ready to work with clay for your chosen firing range.

If you decide to try and rescue your current clay it's likely you will have to test and modify every batch. I'm guessing you are a new potter and while fixing your current clay is probably doable I would suggest removing this obstacle from your path of learning to make pots, might make the journey easier at this point. 

[Tina01]

4 hours ago, Min said:

I think you need to decide if you want to try and fix your current clay or try and find a new supplier who can sell you a ready to work with clay for your chosen firing range.

I want to try both, however now that I've found a consistent type source, need to know what am I doing wrong and what to tweak. 

@Babs says roll a coil around your finger, shouldn't crack. 

I did so and it was relatively smooth, but when making the slab it's all cracked at the bottom surface. 

I know there might be many factors involved, but want to know most probable ones. 

e.g. does it need to be mixed with bentonite, if so, how much? does it need more water? more wedging? adding temper (cattail)? should I sieve it? should I set it aside to rest after mixing with water? or should I just work on a non water absorbent material rather than wood? or something else? 

 

[Babs]

4 hours ago, Tina01 said:

I want to try both, however now that I've found a consistent type source, need to know what am I doing wrong and what to tweak. 

@Babs says roll a coil around your finger, shouldn't crack. 

I did so and it was relatively smooth, but when making the slab it's all cracked at the bottom surface. 

I know there might be many factors involved, but want to know most probable ones. 

e.g. does it need to be mixed with bentonite, if so, how much? does it need more water? more wedging? adding temper (cattail)? should I sieve it? should I set it aside to rest after mixing with water? or should I just work on a non water absorbent material rather than wood? or something else? 

 

If your clay was my recycled,or like a tonneI bought behaving like yours, I would add " fines" which can get lost  after throwing pots. 

@glazenerd has a magic solution, and or add bentonite.

But it is hard to judge without hand on it.

If the board you are working on is very absorbent, your clay may need to be wetter  , or you could roll on a canvas or a cloth.....

Areyou releasing the clay from the board during the rolling process. Compress that surface by running ribs on it.

You plate mold should be coated with a releasing agent, green soap, oil sprayed. It looks like it has caught on the rim where it has cracked on left hand side. This would stress your whole pot.

Your plate may need slow drying. It is shrinking quite a lot.

As glazenerd wrote, change one thing at a time.

I think you are closing in on this, keep testing. 

Don't prejudge  on the "Masters " .they got where they are because they observe and test ad infinitum. Don't have to pick up all they say   just what is relevant to you. All blinkers off in this game

Edited November 5, 2022 by Babs

[glazenerd]

Tina:

Your new tan clay is medium + plasticity. Common for clay to be smooth on one side, and textured on the other when you first start rolling it out. Most of the cracks are on the edges: which is just stress from being rolled. It could use some help; but not much. You can start with 1% bentonite additions. I did not bring up the new clay in my other post, to avoid confusion. Upon viewing it; my initial thought was to use it in part with your reddish clay to help even out PSD (particle size distribution). Common to blend clay to help with plasticity, working properties, and fired properties.

You made the comment. that both the clay and bentonite had the same volume. Do not be deceived by that: bentonite is ultra fine particle, and the trapped air makes up a large part of the volume.

Tom

[Tina01]

16 hours ago, Babs said:

If the board you are working on is very absorbent, your clay may need to be wetter  , or you could roll on a canvas or a cloth.....

it's an A2 drawing board , made of chipboard / MDF

16 hours ago, Babs said:

Areyou releasing the clay from the board during the rolling process. Compress that surface by running ribs on it.

compressing it with rib before the final thickness is of no use and from my experience at the gaged level (~6mm) is just hiding the the problem (cracks), not solving it. They will later show up as what you've seen.

16 hours ago, Babs said:

You plate mold should be coated with a releasing agent, green soap, oil sprayed.

it was. and the circumference of clay was certainly free.

16 hours ago, Babs said:

Your plate may need slow drying. It is shrinking quite a lot.

it was wrapped in two layers of very thick towels. 

Thank you btw, my question for now was about the cracks in rolling stage bc it had happened to me with every type of clay I have worked with so far. Two types of ready to use, one recycled and the one that is dry/raw and I'm trying to process. 

[Tina01]

16 hours ago, glazenerd said:

thought was to use it in part with your reddish clay to help even out PSD (particle size distribution).

No, I probably won't mix the reddish one bc I don't have enough, and also for the acidity. So I will try bento... but regarding PSD, 

It has far less impurities than others. photos show the remainder in sieving, after washing (7 times)  and disposing water each time to dump any sutck fine particles,  I  remained with particles that were sink almost immediately and clear water.

After drying, they were still like dried clay (by color and crack pattern), are those just fine sand that are clay like color? 

macro shot:

and should I dispose them or let them to be part of the body?

Edited November 5, 2022 by Tina01

[Babs]

That cracking at edges when rolling shortish, i.e. low plasticity clay body, is common.

Releasing clay between rolls, rolling in different directions,

rolling in a gentle manner can alleviate this.

From your wedged slab, cut a slice close to the thickness you require, the less handling the better imo. i.e. less stretched

Clay may need to be  a little wetter.

Try rolling on a canvas.

Just thoughts.

[Babs]

Btw if you are sieving and washing, you msy be throwing away the fine particles you require for plasticity

[Tina01]

32 minutes ago, Babs said:

Btw if you are sieving and washing, you msy be throwing away the fine particles you require for plasticity

Thank you. Yes I  knew that, those were what didn't pass the sieve for a test, therefore I washed them to find out what they are actually and whether they are beneficial or harmful, in order to find out if I have to sieve all the dry powder I've bought or not.

 

[Babs]

46 minutes ago, Tina01 said:

Thank you. Yes I  knew that, those were what didn't pass the sieve for a test, therefore I washed them to find out what they are actually and whether they are beneficial or harmful, in order to find out if I have to sieve all the dry powder I've bought or not.

 

So the grit you have washed out is from clay powder you bought?

Might be essential for hand building and sculputural forms.

On the other comments, cracking as shown when rolling is quite common.

Rolling stretched the ribbing over really helps with my clay.

[Babs]

https://www.instagram.com/p/CifWcsnugTo/?igshid=YmMyMTA2M2Y=

This guy says some where some clay he works with us up to 50% sand!

Have to change expectations, he is adapting how andxwhat he makes to suit the clay body imo

 

Edited November 6, 2022 by Babs

[glazenerd]

Tina:

When deciding what to add or remove in a clay body; it comes down to application and firing technique. 1. Functional or non-functional. Functional has specific limits, non-functional has none. 2. Firing- pit, kiln, raku: different firing techniques create their own demands on clay. So before I can answer: how do you plan on firing it? What temperature (cone) do you plan on firing it to? Are you making functional or non-functional pieces.

Tom

 

[Tina01]

55 minutes ago, glazenerd said:

Tina:

When deciding what to add or remove in a clay body; it comes down to application and firing technique. 1. Functional or non-functional. Functional has specific limits, non-functional has none. 2. Firing- pit, kiln, raku: different firing techniques create their own demands on clay. So before I can answer: how do you plan on firing it? What temperature (cone) do you plan on firing it to? Are you making functional or non-functional pieces.

Tom

 

Thank you Tom. 

1. Of course functional. (perhaps sometimes decorative, like very small figure sculpture or calligraphy or maybe some ornaments)

2. only firing I can do is using charcoal as fuel, it's not very difficult for me to make a temporary kiln with breaks. I hope I can get to 900°C (1652F) or above, using charcoal and a blower. that should be a cone 4 I think?

btw I just made a psd test , it's  my new clay after sieving.  might be useful:

[glazenerd]

Tina:

This test tells me a lot: at 10min. indicates your clay has very little fine particles.  At 1hr.15 min it is completely separated. Your clay is mostly comprised of 2+ micron particles; which is large in the world of clay. It also tells me your clay has no appreciable amounts of sodium, potassium, or calcium. I have tested wild clay that has stayed suspended for several days because of the feldspar content and sub-micron particle size.  Run the same test using your bentonite: see how it goes.

Google two things and check to see if they are available to you. 1. potassium fertilizer; which should show up at local farm or garden shops. If they have it: what is the potassium content, and how much phosphates?  2. Fullers Earth: which is fairly common in the Asian markets. Given the temp range you are firing to: Fullers Earth would be more beneficial for many reasons.

Much easier for North American, European, and Australian potters to fix things because we have easy access to many different materials. There are many areas that availability is limited: if any exist at all.

Tom

[Tina01]

On 11/3/2022 at 2:03 AM, glazenerd said:

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).

@glazenerd Regarding that clay, it is certainly acidic but doesn't have wide psd. I took this photo again today, 5 minutes after stirring both:

as you can see there's no gradient anymore as in the last week photo:

It had caused by the reaction of acids and baking soda which release CO2 gas and those gas bubbles prevent the particles to settle down. 

Upon stirring them again today, I found that again some lumps had been formed in the water-only container but not in the right one. Should I try this (look for lumps) with the new one? I already have that in water for the psd test . Or any clay may form lumps staying under water?

[Tina01]

4 hours ago, glazenerd said:

at 10min. indicates your clay has very little fine particles.  At 1hr.15 min it is completely separated. Your clay is mostly comprised of 2+ micron particles; which is large in the world of clay. It also tells me your clay has no appreciable amounts of sodium, potassium, or calcium.

Thank you a lot, although it was disappointing! 

4 hours ago, glazenerd said:

Fullers Earth: which is fairly common in the Asian markets. Given the temp range you are firing to: Fullers Earth would be more beneficial for many reasons.

Does it have any other name? I can't translate it. Or what does it's made of? and what is the mixing ratio? 

4 hours ago, glazenerd said:

Much easier for North American, European, and Australian potters to fix things because we have easy access to many different materials. There are many areas that availability is limited: if any exist at all.

Absolutely! and unfortunate for me.

Edited November 6, 2022 by Tina01

[PeterH]

1 hour ago, Tina01 said:

Does it have any other name? I can't translate it. Or what does it's made of?

Fuller's Earth https://en.wikipedia.org/wiki/Fuller's_earth

Fuller's earth is any clay material that has the capability to decolorize oil or other liquids without the use of harsh chemical treatment.^[1][2] Fuller's earth typically consists of palygorskite (attapulgite) or bentonite.^[1]

Modern uses of fuller's earth include as absorbents for oil, grease, and animal waste (cat litter) and as a carrier for pesticides and fertilizers. Minor uses include filtering, clarifying, and decolorizing; active and inactive ingredient in beauty products; and as a filler in paint, plaster, adhesives, and pharmaceuticals.^[1] It also has a number of uses in the film industry and on stage.

Probably bad news, cat litter may often be calcium bentonite. 

See Digitalfire for the difference https://digitalfire.com/material/bentonite

Edited November 6, 2022 by PeterH

[Tina01]

3 hours ago, PeterH said:

Fuller's earth is any clay material that has the capability to decolorize oil or other liquids without the use of harsh chemical treatment.^[1][2] Fuller's earth typically consists of palygorskite (attapulgite) or bentonite.^[1]

This is so confusing, it means that some bentonite can be Fullers Earth? bentonite has calcium sodium potassium types with extra fine particles and plasticity but FE also contains bentonite, isn't plastic, and has the same metals? 

now I have doubts which one do I have?  is it bentonite or FE? any suggestions how to find out? (except for eating bc digitalfire.com says FE strongly sticks to the tongue).

one table spoon water:

one tablespoon of it inside tube, but water couldn't penetrate more than 3mm so I  shake and stir it:

not disolved, full of lumps, so I dumped it out, still stuck at bottom and dry parts:

what that came out:

is it bentonite or FE  or something else? 

Edited November 6, 2022 by Tina01

[Tina01]

9 hours ago, glazenerd said:

Run the same test using your bentonite: see how it goes.

couldn't run the test (see the pictures above). It was an immediate transform. 

[neilestrick]

I'm not trying to be a downer, but I think your best bet is to contact another potter in the area and see where they get their clay. You could spend a ton of time trying to figure this out and end up not being able to fix it. Most clays are not used alone, but are blended with other clays to achieve the properties you need, and not all clays are good for making pots. The other thing you need to consider is your ability to fire pots. If you can only get to 900C (cone 010), then you're not going to be able to make functional work. Pit firing and other non-functional techniques can make some really great work, though. You really need to be able to get to 1000C in order to use glazes.

[Tina01]

8 hours ago, neilestrick said:

I'm not trying to be a downer, but I think your best bet is to contact another potter in the area and see where they get their clay. You could spend a ton of time trying to figure this out and end up not being able to fix it. Most clays are not used alone, but are blended with other clays to achieve the properties you need, and not all clays are good for making pots. The other thing you need to consider is your ability to fire pots. If you can only get to 900C (cone 010), then you're not going to be able to make functional work. Pit firing and other non-functional techniques can make some really great work, though. You really need to be able to get to 1000C in order to use glazes.

Thanks for your suggestions and information. I might do so but since joining this forum and doing some research I now know a lot more. I'm interested in learning so perhaps I'll do both.

but I had no idea that a handful of dirt is so complicated! making wine was certainly easier than this!