Tina01
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Posts posted by Tina01
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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?
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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.
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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.
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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.
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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.
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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.
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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?
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@PeterH These were pretty interesintereg! Had no idea about it! I'll try to reach more people that possibly know the regions better, however living in remote areas makes it difficult, on the other hand it's nice if I would be able to collect my own. at least I'll know what's inside!
Thanks for the links!
@HulkThat was interesting either! hopefully I could be able to do some research through them. Unfortunately there was no supplier in that page form Georgia, but I will keep trying, currently was able to get some workable clay (still no professional specs on them) with help of some friends. but next steps would be much more difficult! (glazes, stains, etc...)
thank you!
You guys are awesome!
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12 hours ago, oldlady said:
oh! that is very bad stuff, i do not want to call it clay.
yes, indeed, unfortunately :-(
12 hours ago, oldlady said:seeing it makes me feel like i should send you some good clay but i cannot afford the shipping costs. is there any other country that you can buy clay from?
thank you so much for your kindness! Answering my questions is a huge favor one can do for me :-)
it would be easier for me to search for natural clay and process it, rather than ordering, waiting, paying for the clay, shipping, and also paying for customs (as an imported good)!
12 hours ago, oldlady said:there is no future in trying to work with whatever that stuff is.
Again yes, I'm so disappointed. :-( but won't just leave it.... I found the expensive white one is also available on Amazon in terra cotta
https://www.amazon.com/KOH-I-NOOR-013170700000-Keraplast-Drying-Modelling/dp/B0094FZZWU/
but I can't use it as earthenware, correct? My goal is to make something functional, even just a flower vase.
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On 10/23/2022 at 5:42 PM, oldlady said:
drying out the clay in thin slices works very well. once the clay is totally dry, the water you add will immediately be sucked up and the clay will soften. if the clay is not totally dry it will not work. left overnight, the clay you have wet will be usable the next day. i do this in a bucket and collect dry bits as i work each day. when i want to use it, i add the water to just above the dry clay and let it soak in overnight.
Well I found that I should buy a different brand, except for the third one which I'm not into modeling, sculptures, talking to my friends.
however I tried both methods, but both are time consuming. with wetting wet, the inner region still is stiff, needs experience to know how much water is needed and may take much longer than a day depending on clay amount.
with dried slices, I added water to the level that you've mentioned but they turn into thick slip so again I had to remove water, (pouring on a fine texture fabric above some folded towel). that again takes time. perhaps it's because of different clay.
during that process after failure I tried to filter the clay using a strainer, and found various sizes of natural stones in 1kg (about 2lbs) of it, and guess it's abnormal and also being short, nearly worst clay possible!
the ones that didn't pass:
and many that passed:
now I set the clay aside to drying , having no access to bentonite, what can I add for increasing plasticity? I have some iron oxide powders (red and yellow) and zinc oxide(white). will they be helpful?
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1 hour ago, oldlady said:
tina, could you please identify your location for us? i do not think you are in the United States but in the country of Georgia. that makes a very important difference so we do not give you information you cannot use.
from experience, i learned that trying to wet clay that is already partly wet does not work. drying out the clay in thin slices works very well. once the clay is totally dry, the water you add will immediately be sucked up and the clay will soften. if the clay is not totally dry it will not work. left overnight, the clay you have wet will be usable the next day. i do this in a bucket and collect dry bits as i work each day. when i want to use it, i add the water to just above the dry clay and let it soak in overnight.
if you know of people who use this clay, talk directly to them to ask what they do.
Thank you
yes, sorry about the confusion! not in US, but in a small town in southern part of the country. That's why I'm so limited in availability of material and also online shopping.
Also thank you for sharing your experience. I will try this either among the other method of earlier post.
Unfortunately don't know anyone in person but my best guess is that those had left at the store for a long time so I will try another store. also will look if I could find a pottery workshop .
thank you for your help again.
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2 hours ago, PeterH said:
This sort of idea is often recommended:
https://www.clayartcenter.org/clay-art-center-blog/2020/3/how-to-rehydrate-bone-dry-clay-easilyVideo of the same idea on a slightly smaller scale:
Thank you, will try that for sure! I hope it works. Could have save me a long time and lot of work if knew that earlier.
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On 10/20/2022 at 11:36 PM, Babs said:
Crack the dried clay down as much as possible snd then slake.
Sand is your prob.
If already a handbuiling clay ,dnt need it. Coil abit of clay and bend the coil around your finger, shouldn't crack.
On 10/21/2022 at 9:16 PM, Callie Beller Diesel said:Some white firing clay bodies, especially some mid-fire porcelains, don’t reclaim well unless you have all the components added back into the mix. IThat’s because some of them have neph sye as an ingredient, which is slightly soluble, and it affects thixotropy and plasticity. If you add or subtract too much, it can make your clay extra short. Because you’re reclaiming clay that hasn’t been used, I don't think this is your problem, and drying the batch that doesn’t have the sand added will confirm or disprove that.
BUT.
If you didn’t wash the sand and it was from an ocean beach, there could be any number of possible solubles that will also mess with that particular point of chemistry. If your clay body is one of these clay bodies that doesn’t like to be reclaimed AND you added extra sodium or calcium solubles left behind by sea water, that would also explain this reaction. Especially because you let the slurry sit for a few days, and everything had a really good chance to marinate together.
Thanks to everyone for their help.
It seems you all agreed that adding sand caused the problem. So I threw them away and probably won't add anything in the future.
As for buying clay, there's not many options to choose from, there are only 3 types available here, and the packaging is so poor quality that they are just softer than leather hard and wedging them is quite hard. I don't know how others deal with it and wonder what to do with them?
1. Normal, raw wild clay (perhaps with some processes).
2. Clay mixed with a plant called Typha latifolia, (bulrush?) advertised to be more crack resistant than the regular one.
3. White, air dry clay, that is very expensive. better packaging, softer, but I guess it's only for sculptures and not firing.
And there's no cone or any other info available.
I bought all, however don't know how to properly add back water to them. Is making a slab and submerging in water or forming to a bowl then pouring water in it is a good idea?
Thank you again everyone!
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1 hour ago, Min said:
I wouldn't do this until you have fired some test tiles to see what the sea sand is doing to the clay. If it contains calcium (from seashells) it could really affect the firing. Also 20% sand is a lot for making small(ish) pots like in your example. I'ld suggest starting from the beginning and making some tests with 5%, 10% and 15% sand. Wash the sand, dry it then weigh out the amounts and add it do dry clay and slake it down, mix it up with a paint mixer then when workable make some test tiles and fire those (with no glaze) to whatever cone the clay is rated for then examine the test tiles.
Was it sea sand that was recommended to you or just "sand"? In ceramics when sand is mentioned it's silica sand. Silica sand comes in different mesh sizes, the smaller the number the courser the sand.
I'ld also try making some pots without any added sand, clay might be just fine the way it is.
No, actually the clay was dried (not used from purchase time , I don't have access to raw or wild clay if that's what you mean). So I really don't know if it already has something in it or not. I guessed not, therefore added the sand.
It was not recommended or special, as I mentioned, just picked them up from a beach.
Oh about the silica, didn't know that either, the guy on youtube says add sand, wood ash, crushed fired clay, etc... for absorbing thermal shock...
yes... I won't add anything more to the currently recycling batch and also will compare it with new ones I should buy.
When it is percent, how does it differ if it's a small pot or big?
except for these additions to handle thermal shock, what can I add for increasing plasticity and avoid cracking in drying and firing time?
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34 minutes ago, Hulk said:
I'd missed the percent sand.
Now I'm curious how my clays would behave with twenty percent sand added.Looks like you smoothed those small cracks over.
The big cracks, do they still appear when the piece is allowed to shrink - removed from the mold sooner?the small cracks on the outside yes, although I knew it won't help and they shouldn't appear in the first place. What is visible in photo are from those on the bottom side (on the mold).
Yes, that was disappointing so I removed them and added back to the rest of chunk with a little water stored in a plastic bag.
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48 minutes ago, Jeff Longtin said:
My hunch is that there is too much sand in the clay. I would have suggested you test the clay first before adding that much sand.
Has the sand been washed? I've never worked with sea sand but I wonder if it adds salt to the clay? Do you know the mesh size of the sand? A smaller mesh would have less impact on plasticity.
Yes, you're right, I should have test it but since adding sand was more easier to clay/water mixture in bucket than to the clay later, I did that.
The sand was not washed (if you mean by tap water) I really can't tell the mesh size, but I collected them from the beach (will attach a photo) .
The most weird thing is if they clay is too wet, it will be sticky but shouldn't crack. However mine was cracking while shaping, flattening, bending... not only at edges but all over the slab.
leaving it to dry and wedging helped a lot, but still far far from a regular workable clay. By the way, why there are some lumps still in the bucket and it's not uniform after 6 days? I hardly think that those disolve at all.
the lumps
sand grains, pencil for reference
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1 hour ago, Hulk said:
I like recycled clay!
It's a bit of work, on the other hand, the material is "free."
I'm bagging the clay when it is just a bit wetter/softer than what the vendor provides, however, not so wet that it's very sticky - I can wedge it without having to then scrape off my hands, and although some bits stick to the wedging board, it's not much.Well mine was a bit wetter and more sticky but it was cracking at the same time.
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1 hour ago, Babs said:
The mold ,steel bowl , needs to be coated with something to prevent clay from sticking to it as it dries.
Strops of damp newspaper, plastic wrap, green thick dishwashing liquid etc.
How did you wet the clay down?
Was the clay previously thrown into pots? Can lose fine particles which make clay plastic.
Make a slurry of clay leave for a couple of days, spread out on plaster board to dry , wedge and see if it is better.
May need some bentonite to jncrease plasticity.
The clay was not fired or anything, just had dried in its packaging.
I crashed the blocks to the size of golf ball chunks (more or less) then put them in a bucket, filled with water.
After 4~5 days and stirring everyday , there were still a few lumps not dissolved in it but I didn't pay attention to those. Then according to some recipes I mixed about 20% sea sand to it and put it in a pillow case to dry.
I have another bucket with same clay sitting for a week now, but still it has some clay lumps in it, I guess I should use an electric mixer.
But for current batch I'm not sure if it's because of added sand or not. I can't pull them out so either I have to discard it and don't add anything to the new bucket, or if sand is ok redo the wetting procedure again as you told?
p.s. No, they are just regular clay (not a well-known manufacturer or brand) but I'm sure they're good as I've seen people use the same without problem.
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Hi I'm Tina and just joined here, I'm a total newbie in pottery.
I had some clay that were bought a couple of years ago, obviously they were bone dry. I attempted to recycle them and start making something. However it didn't go well.
The problem is that although the clay was wet and sticky (to wooden board and my hands), at the same time many small cracks were forming when I tend to flat it with a rollor. or making a coil out of it.
I tried to wedge it for half an hour, adding a bit more water, but that didn't help much. small cracks all over the slab and more severe cracks around the edges.
what could be wrong with it and what should I do?
more info with pictures:
Thank you so much for helping me!
Why my clay acts like this?
in Clay and Glaze Chemistry
Posted
it's an A2 drawing board , made of chipboard / MDF
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.
it was. and the circumference of clay was certainly free.
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.