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Hand-built Sculpture Disaster


LeeAnets
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I've been doing clay for a while now, so not a total noob, but have had my biggest disaster in clay to date. I have to admit I have not done a ton of hand building in the last few years, but have done enough to know the basics. 

I was hand-building some larger pieces. Scored and slip attachments to sides. (The same way I have scored for ten years without having issues.) I dried them very slowly under plastic, as I live in northern Arizona and things dry way too fast here. 

They were built with Laguna's Rod's Bod. I built each piece one at a time, during the day, so the slabs would be close to the same moisture. I throw out my slabs for each piece all at one time, by hand, and finish by rolling them between dow rods to get thickness relatively close. I kept extra slabs covered while working on the main piece.

The only thing I can think that may have had an effect was that I let these dry in my garage. (We just moved into this house, so I consider this a variable I haven't dealt with before. In my last house, I dried my hand built items inside the house, and had no issues.) My garage is not heated, but attached to the house, so it never got below 45 degrees F. But the temperature ranged from probably 70 F in the day to 45 F at night. It never fell below freezing, though.

Everything looked fine, but when they were bisque fired, most of the attachments fell off. (see photos)

Could the range of drying temperature have cause my problem?

I am racking my brain trying to figure this out. Please help...

IMG_9729b.jpg

IMG_9730b.jpg

IMG_9728.jpg

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When the bond is not right they can jump off.

Reasons -here are a few

slabs are different moisture content- Slabs are to dry to work well. my guess is this one

wrap them fin plastic for at least a day to even out next time

not enough slip  used or  enough pressure when joining

Not enough time wraped up to equalize moisture content

bisque fired to fast ( I doubt this one)

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Okay, thanks Mark C. Two things you said that it might be...

I will try wrapping all slabs for a day before using them. 

I am also wondering if I did not use enough force when I paddled the pieces together - like you said. I may not have had enough "back" pressure behind it.

Thank you.

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Min - I did see slip come out; I always have to clean it up with a sponge. I do wiggle pieces together where I can (ie: especially vertical walls going onto a slab base), but I wouldn't know how to do that to the parts that wrap around the main structure. How do you giggle yours?

Russ - I will keep that in mind. Many times it happens naturally in the process if I have scored, added slip, and then see my scoring isn't enough. Then I will rescore on top of the slip. 

Again though, I have no idea why this was the time that everything went nuts. I've never experienced such an unsuccessful bisque firing...

Thanks everyone!

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Cool sculpture Lee!

All the other joins survived ok?

fwiw (I don't do much joining - handles, knobs, sprigs), I wet the clay on the receiving end a bit before scoring - just a wet fingertip, damp brush, or sponge; the sheen dissipates as the water is absorbed into the clay, then I'll score. Typically, I'm not joining bits that are exactly the same wetness. I'll also wet the piece to be applied if it's a bit dry, depending. I apply slip to the piece to be applied after scoring, and that only so that it will squeeze out to then be smoothed into the crease, for if both pieces are dampened just right, they'll join without slip. Uhm, I said without slip, however, others may point out that it depends on the clay.

The older gentleman in the Ingleton videos points out in his teapot making clip that scoring isn't necessary (for his process), which I misremembered as slip isn't necessary (about 8:40): 

Throwing / Making a Pottery Teapot on the Wheel - YouTube

There are variables, to be sure. Van Gilder, in some of his vids, wets, but doesn't score or use slip.

That your scoring is so clear (with a few exceptions, where the breaks are) - tells us somethin. Will you post back with more pics of your cool sculptures?

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Great info and thanks for the link.

I did have two survive the load and will go forward with glazing those. (Again, another reason I’m perplexed!) As soon as they finish I will post them. Thanks for asking!

In the mean time, I will try some testing with different variables and see what happens. 
 

Thanks!

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I have seen this sort of problem in the past with student pots when I was teaching HS. I don't know as it is a perfect solution, but here is my take.  If any air is trapped in between the two layers of clay that are joined, it may expand enough to cause some expansion cracking thus weakening the joins and causing the pieces to fall off. We used to put pin holes on the inside of the pot where the so that the bottom surface could let air escape into the pot as it expanded. This was often a problem with a lot of the "fairy houses" we used to make, as the students would want to add layers of clay over the base pot for facades. After a few times of trying to figure why some would survive and others would not we started to try the pin hole technique. Had very few problems after that. You may also try magic  water instead of slip, as this was also an improvement in overall construction processes.  You have to remember that HS classes I taught were 50 minutes long (subtract 15 minutes for set up and clean up)  and therefore projects had to be planned out, slabs cut to size, assembled, decorated and finished over the course of several weeks, much the same as your situation.

 

best,

Pres

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I left each piece sitting under plastic for a week. Then removed the plastic and left them sitting for another two weeks. 

Although, especially looking at the second picture at the base of where the attachment was I wondered if there was something trapped under there. 

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11 hours ago, Pres said:

If any air is trapped in between the two layers of clay

I am with this one...

Especially if you were trying to line up edges well, it makes you seal up the edges first, trapping the air. 

Then, unless you push so hard you break the seal, it'll feel good and attached no matter how hard you push.

What does the scored side of that fish shaped piece look like?

Those score lines shouldn't be visible at all, that clay should be homogeneous. It had to be air, or just not enough "scoochy scoochy". (That's a technical term I love as learned from a HS teacher on YouTube!)

Then Shrink either drying or firing, made them break off. If attached well, you may have still seen cracks where it cracked. Ar other attachments still on and cracked?

Sorce

 

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12 hours ago, Pres said:

If any air is trapped

So as i have been studying this...I am wondering whether this was the culprit. And I am thinking about your pinhole idea, Pres. Here's why...after joining and paddling the pieces together (maybe not having enough pressure as well) I cleaned up the edges and smoothed the creases over with a tool and sponge. That might have sealed their fate, because in drying, there would have been no way for air to escape at all. Now, If I had joined them perfectly there may have been no need for any air to escape, but...

What does everyone think?

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@JohnnyKgood call, on the dryness of the slabs, sometimes leather hard slabs seem to be damp enough, but really aren't. I usually prefer to assemble when slabs are cheese hard than leather hard. 

@LeeAnets The formula use has been around for years. . . 1 gallon of water, 3 tablespoons of liquid sodium silicate, 1 1/2 teaspoons of soda ash

best,

Pres

 

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38 minutes ago, JohnnyK said:

were too dry when you scored them

The slabs were wrapped in plastic and attached probably within 2 hours of making them. I worked on the main piece (walls and base) then added the main attachments next. I seriously doubt they were leather hard by that time, being wrapped tightly in plastic.

 

1 hour ago, Sorcery said:

Those score lines shouldn't be visible at all, that clay should be homogeneous.

 

Maybe my scoring is so visible because I am too aggressive with scoring?? 

Also, I used a ton of slip on both sides - the base and the attached piece(s).

Now, I will say that I did attach them right away - should I wait a few minuted to let it absorb the slip more?

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I'm anti slip. Just score and water droplets from a needle bottle. Your skip could be the culprit if it's different. I believe slip in a jar can become so bacterially different, it could effect the drying rates. Especially taking into account @liambesawnotes of Fungi gathering metals and minerals, it's what they do.

This picture shows best the smooth parts that were attached well.

1772340151_Capture_2020-12-27-10-54-12.jpg.b83bb6e445b12809afb13e7b3e3f7a77.jpg

 

If you concave the attachments slightly, so the center is first to contact, you will never trap air, or begin at one side and roll it out the other side.

If you're a criminal, like they do fingerprints!

Sorce

 

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1 hour ago, JohnnyK said:

From what I see in the last photo, your pieces were too dry when you scored them, of uneven dryness between the pieces, and not enough slip was used between the pieces. AS @sorce says: "Those score lines shouldn't be visible at all, that clay should be homogeneous".

I agree on this point from that photo -also a lack of slip-I just do not see much slip in there.

Edited by Mark C.
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On 12/28/2020 at 3:38 AM, LeeAnets said:

Other attachments were on, but not cracked. One sculpture came out with no problems. Of course I have only bisque fired it so far.

 

 

Air doesn't cause explosions,  moisture does.

Score your piece one direction ,attachments right angle scoring to first direction, slip deflocced and wiggle each piece into place hand inside and firm pressure.

Bet the one which survived was first constructed as stuff drys out waiting, waiting .

I sprigg attach thus and then go over sprigg and edges of join with slip...nothing trapped inside  so that part of your assembling not the problem.

Stuff too dry to start with could be.

My main body usually softer..wetter than sprigg..like handle to mug.

Basically need to meld attachment to body of pot firmly , if try to detach after joining, should be difficult and messy.

 

 

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