Cracking in drying

[MattA]

This is one of my bigger pots (about 14") that has survived the drying, next step firing. Hopefully soon, like you I had a bit of trouble tracking down a gasfitter to do the job.

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Simple hand formed block with carved inside & underneath.

[GavinG]

Just another couple of ideas - Maybe make the pots a bit thicker?

And with the white suiban, fired on a slab on the same material, I've always found it helpful to fire on pads of fireclay and sand (50/50) - no warping underneath, supports the bottom, and doesn't stick to pots.

Good luck,

Gavin

[vgarth]

Thanks Matt. that's an interesting idea for shaping a pot, carve out from a block. I might try that at some stage - it certainly looks lovely. I wish you firing success.

And also Thanks Gavin, already the next pot I'm working on is a bit thicker, since the slabs were cut with a wire harp and I couldn't get them any finer. I wondered about rolling it a bit finer with a rolling pin, and was afraid that might cause the cracking later, but from what Penny of Mudlark pottery has said, it looks like I can give it a bit of a roll, if it's been well banged first. Anyway, current pot is definitely thicker, we'll see if too thick as it goes on. I think I sometimes fear thick as course, and ugly, which in most throwing eg tableware, it is. But bonsai pots are allowed to have some solidity, I guess.

And thanks for the suggestion of how to make the pads to put under it. I was planning next time to use smaller pieces of same clay, but fireclay and sand sounds good.

But that leads to another question - When people recommend sand to put on the kiln shelf or add to clay, do they mean ordinary sand I get in a bag at the hardware? Brickies sand basically? Or some special type from a pottery supplier?

And Penny, you said to dry upside down, on something soft ( I have some sheets of foam rubber and now know what to use them for, thanks) but would you support the inside of the base while it's drying like this? Put some blocks of foam rubber in there maybe? I'm worried the floor will sag.

And yes, Penny, you're right, the Feeneys red raku does have grog - back in class I looked at it again and it's full of a fine grit. Just didn't recall it as being groggy compared to Feeney's BRT which must have a courser grog. And I wasn't throwing, so I noticed it less.

Once again my unending gratitude to all, including the Ausbonsai people, I did fine a printview button, after getting out of the post page, and it printed successfully, as did the file Matt sent me.
Val Garth

[MattA]

Apart from a few pinch pots all of my pots are carved, I have also experimented with marbling different clay bodies together to look like they are carved from a block of stone (I hope)

[mudlarkpottery]

Hi Val.
Any sand will do. You can also use pieces of fibre under the feet. That will smooth out any unevenness in either the shelf or the feet and will help as the pot shrinks during firing. It would be a good idea for you to support the base of your pots as they are drying. Scrunched-up newspaper will do at a pinch. As the clay shrinks when it is drying, the foam or newspaper has enough give in it to move with the clay - otherwise, more cracks.
Penny.

[vgarth]

Thanks again Penny.

[Pat K]

Hi Val,

You've had so much good advice that there's nothing really for me to add except to reiterate what has already been said and that is to be always aware of the mechanical properties of clay.
I don't want to teach you to suck eggs BUT......

#1. As clay looses moisture it begins to shrink

#2. Joining sections of clay in different stages of drying is doomed to failure.

#3. Putting these pots (#2), into a plastic bag in the hope of evening out the moisture content is hopeless....the damage has already been done!

#4. The solution....put the sections of the pot into an enclosed space to even the moisture BEFORE construction begins.

This is my method and I haven't had a cracked pot in 4 or 5 years!

Good potting and cheers,

Pat

[vgarth]

Thanks Pat, I will do better next time I hope. I thought the pieces were evenly moist when I joined, all came from the same bag of clay, but some waited around a bit longer, in the other room, perhaps one lot dried more than the other. Hmmm, on recollection, were all done in the same session? I'm not sure. Now I think about it, I finished a smaller pot first. Next I started the big one, and some slabs were rolled out, cut and and then time was up, they were wrapped up together for constructing in the next class. Then when I arrived, I found I couldn't count. This design didn't need two long and two short sides, I needed more short pieces. I did have to roll and cut more the next week. That could have been a big part of the problem.
The latest pot, simpler in shape, (just a rectangle) has all been done in one session except for its feet. And in fact the feet were cut but not joined, and are wrapped with it. And all of it did come from one bag of clay, and was banged not rolled, and cut with a harp cos that's what was available. So I really hope this latest one will be better. If I can get it right, I can move back to the harder shape, see if I can get it right with that.
Thanks again.
Here's a pic of the latest one, not fully constructed yet when I took this shot:

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Val Garth

[cuwire]

Hey Val thanks for posting your work.

If I can get it right, I can move back to the harder shape

I do not think that what you are doing here will prove to be simple as you think and you are a very gutsy potter with the sizes you are working on.
Your new endeavor will be to keep the sides straight in this precise geometric shape if they bow in too much the whole effect will be lessened.

I think that this shape simple as it may be is classic minimalist I first saw a similar pot in an artists studio with Fig planted it looked so striking.

Any way I am on my second and learning a bit as I go but when I get one to be a perfect oblong after drying I will be happy ... but then there is the horrors of the kiln.

Mine are 200x300x95 yours appears to be a substantial half metre in the direction i can see.

Keep on potting

Cheers David

[vgarth]

Cheers David,
36 cm on the long side - not up to half a metre yet.
Val Garth

[vgarth]

Here's the latest attempt, set aside to dry now, draped and in a humid cupboard. Forgot to take my sprig moulds to class today, so improvised a decoration. Probably not really bonsai style of decoration... we'll see how it looks later.

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[bonsaipotter]

Hi Val,

I searched through my old bookmarks for some great reference sites about the things that can go wrong. You might like to check them out - I think they are really good.

http://ceramicdefects.com/df01.pdf
http://www.cheminfonet.org/art/ceramics101.pdf
http://www.frogpondpottery.com/articles/crackwrp.html

Cheers,
Happy Potter

[vgarth]

Thanks Happy Potter,
I will have a look. My latest handbuilt pots are still slowly drying at my teacher's place. I think no cracking so far. None the less, I will check these sites out.
Cheers,
Val

[vgarth]

Well, these were fired successfully right at the end of 2012, but I've been very slow to post. I'm extremely happy with all the advice I was given, and expecially that of Penny at Mudlark.

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Then finally, at home and with no teacher, and doing the firing entirely by myself as well, I have made lots of regular thrown pots and lots of clumpy irregular pots (not too much of a challenge), but also this precise pot made to order for someone. I was very pleased with it.

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Feeling much more confident, though to do it right is a lot of work! But very satisfying work/play.

[bonsaiLov]

What a shame ,looks like you put a lot of work into them, creative