Clay particle orientation and joining slabs

[andrewiles]

I've been watching the awesome videos from Washington Street Studios on YouTube.

One of these discusses the orientation of particles within clay and how this impacts shrinkage when drying:

At around 19:30 he describes how joining pieces of different orientations can cause problems.

I've been handbuilding some slab pots and I'm now trying an extruder. This seems to be a problem. If the z-direction is out of the table, the rolled slab will have clay particles oriented in the xy plane while the extruded walls will be oriented in the xz or yz plane. In either case the walls will tend to shorten in the xy plane more than the bottom slab.

Anyone have thoughts on this? I know @ABCarve was using an extruder in some of this work and I see @penumbra is looking to buy one. I'm starting to dry my first pot with extruded walls now.

 

[ABCarve]

I've been watching the awesome videos from Washington Street Studios on YouTube.

One of these discusses the orientation of particles within clay and how this impacts shrinkage when drying:

At around 19:30 he describes how joining pieces of different orientations can cause problems.

I've been handbuilding some slab pots and I'm now trying an extruder. This seems to be a problem. If the z-direction is out of the table, the rolled slab will have clay particles oriented in the xy plane while the extruded walls will be oriented in the xz or yz plane. In either case the walls will tend to shorten in the xy plane more than the bottom slab.

Anyone have thoughts on this? I know @ABCarve was using an extruder in some of this work and I see @penumbra is looking to buy one. I'm starting to dry my first pot with extruded walls now.

This was the first year I used an extruder. My pots have gone through the bisque firing without a problem. I’m just now starting to glaze. Glaze firing will tell the tale. Stay tuned.

 

[ABCarve]

One thing he didn’t discuss was how grog and other fillers interrupt those platelets.

 

[Colorado]

Interesting post!

 

[ABCarve]

I had two different teachers at university. Both advocated for rotating the slab. Neither of them did it in their own practice. I have done it both ways and haven’t had a problem. The only problem I’ve had was drying to quickly or unevenly. I used to cover my pots only on their walls because they dry out more quickly. I had problems with that technique. However I’ve seen pros use that very technique and swear by it. You must find your own way and that means pots will crack. Everyone will kill some trees along their path. Good luck!!

 

[penumbra]

Phil will be missed. He was such a gentleman and so knowledgeable. You didn't have to agree with everything he said (though he was usually right) but he put it out there for thousands of potters.
RIP, 7/21/21

 

[Bob Hunter]

The only problem I’ve had was drying to quickly or unevenly. I used to cover my pots only on their walls because they dry out more quickly. I had problems with that technique.

Yes I would worry more about slow drying then molecules....

 

[andrewiles]

I had two different teachers at university. Both advocated for rotating the slab. Neither of them did it in their own practice. I have done it both ways and haven’t had a problem. The only problem I’ve had was drying to quickly or unevenly. I used to cover my pots only on their walls because they dry out more quickly. I had problems with that technique. However I’ve seen pros use that very technique and swear by it. You must find your own way and that means pots will crack. Everyone will kill some trees along their path. Good luck!!

I wonder how much of this is due to studio humidity. I'm going to bring a little humidity sensor to the studio next time I go. It feels rather muggy in there and I suspect the RH is high. Higher RH probably means fewer drying issues during slab construction.

 

[andrewiles]

Yes I would worry more about slow drying then molecules....

Yeah, I'm probably getting ahead of myself. I'm finding it hard to control drying with these large pots when I'm not in the studio every day. Bag trick leaves one side drier by the opening. And the part of the pot facing down invariably dries slower. The rotation process is tedious. I'm going to bring one of my pots home to dry so I can manage the drying better.

 

[andrewiles]

Kind of off topic, but for anyone not up to speed on these things I found this presentation useful for basic drying concepts: https://www.yumpu.com/en/document/read/34584431/drying-alfreds-clay-store

 

[ABCarve]

I wonder how much of this is due to studio humidity. I'm going to bring a little humidity sensor to the studio next time I go. It feels rather muggy in there and I suspect the RH is high. Higher RH probably means fewer drying issues during slab construction.

The bigger the pot the more having a greater % of grog or other fillers becomes necessary. Have you looked into using a wet box?

 

[andrewiles]

The bigger the pot the more having a greater % of grog or other fillers becomes necessary. Have you looked into using a wet box?

Funny you ask. I just brought my last pot home to experiment with humidity control. I have it in an unused storage container. Going to start measuring the humidity to see how it changes with occasional lid removals.

Yeah, the pot in this picture is the first I've tried with added grog. I'm limited to what they sell at the local store for now.



This is all going to be pretty comical in the end, since I still haven't even finished firing a pot yet. Getting some glaze test tiles back tomorrow though!

 

[ABCarve]

A wet box has about 2- 3” of plaster poured into the bottom of it. Once it sets up you can add more water for it to absorb. It will keep the humidity at 100% and your pot in stasis until you remove it. It gives the moisture content time to equalize. It does the same as your pot being inside a sealed garbage bag and not just under it. It’s just a lot easier to put it in there.

Funny you ask. I just brought my last pot home to experiment with humidity control. I have it in an unused storage container. Going to start measuring the humidity to see how it changes with occasional lid removals.

Yeah, the pot in this picture is the first I've tried with added grog. I'm limited to what they sell at the local store for now.

View attachment 419218

This is all going to be pretty comical in the end, since I still haven't even finished firing a pot yet. Getting some glaze test tiles back tomorrow though!

 

[August44]

How long would you suggest keeping a newly built pot in a wet box?

 

[sorce]

I believe "Appropriate Drying" is found with a good understanding of "slow drying"(it's not just slow) and molecules.

This is pertinent and recent.
Post in thread 'Pottery beginnings' https://www.bonsainut.com/threads/pottery-beginnings.51798/post-933432

I been contemplating extruder walls for a while. Reckon I'll score mad thread graft points and save that for @penumbras extruder thread and talk about that other thread where you wet joined that one joint.

Sounded too smooth to me, like ....you been hit by....you been struck by .....

Sorce

 

[ABCarve]

How long would you suggest keeping a newly built pot in a wet box?

I let mine sit overnight. Sometimes longer if there are greater differences in component moisture content. I’ve left pots in for weeks when I wasn’t sure where it was going design wise.

 

[andrewiles]

I'm going do make a small pot as an experiemnt. 2 walls rolled and 2 walls extruded. See if there is any difference in shrinkage and warping.

An interesting thing I just learned about drying is that it has two stages before going into the kiln. Shrinkage only occurs in the first stage, which goes until the clay is leather hard. Between leather hard and bone dry very little further shrinking occurs and you don't need to dry slowly. Called the critical point in this slide:

The issue I'm trying to work through right now is this:

 

[JeffS73]

I can tell you that just this last week I had a pot beyond leather hard drying out in the garage where I was firing the kiln, I'd neglected to move it. Pot cracked. It could have been other stresses, I've only made a handful of pots, but I would have preferred to know it had dried slow and even all the way to bone dry.

 

[andrewiles]

Yeah, I'm, finding that when people say dry slowly and evenly, they mean it. I had a pot at the local studio under a plastic sheet and against a wall. It dried out in about a week but had a warped side from where it had dried much faster away from the wall.

Now I'm drying my pots in some storage containers I had laying around. I open the lid for a bit each day. Once the lids go back on the humidity jumps back to 99% within a few minutes -- amazing how quickly the clay releases water.

 

[August44]

Yeah, I'm, finding that when people say dry slowly and evenly, they mean it. I had a pot at the local studio under a plastic sheet and against a wall. It dried out in about a week but had a warped side from where it had dried much faster away from the wall.

Now I'm drying my pots in some storage containers I had laying around. I open the lid for a bit each day. Once the lids go back on the humidity jumps back to 99% within a few minutes -- amazing how quickly the clay releases water.
View attachment 420120

So Andrew you are not using the plaster in the bottom of those storage containers? You're having good luck without that? Nice rectangle!