[Clayart] S crack remedy?

[vpitelka at dtccom.net]

Hi Ken - 
Good advice from Woof below.  Throughout my teaching career, I discouraged students from repairing cracks unless they appeared on a complex vessel or sculpture and where there was a good chance of fixing them.  In this case, if you have a bad S-crack before firing, chances are that even if you tried to repair it, the crack would reappear in the glaze-firing.  You learn a lot more by making another pot than you do by taking the time to attempt repair on a damaged one. 

With fine-grain claybodies like porcelains, when you trim the bottom, it is a good idea to go over the trimmed surface with a smoothly-rounded wood tool (like the back of a spoon, but wood).  The rounded end of the wooden knife that comes in the standard Kemper tool kit works well for this.  This further compresses the clay, decreasing the chances of cracks appearing.  
- Vince  

Vince Pitelka
Professor Emeritus of Art/Ceramics
Appalachian Center for Craft
School of Art, Craft & Design
Tennessee Tech University
Now Residing Chapel Hill, NC
vpitelka at dtccom.net
www.vincepitelka.com 

-----Original Message-----
From: Clayart <clayart-bounces at lists.clayartworld.com> On Behalf Of David Woof
Sent: Thursday, November 12, 2020 5:05 PM
To: Clayart international pottery discussion forum <clayart at lists.clayartworld.com>
Subject: Re: [Clayart] S crack remedy?

Greetings Ken,
happy to see you back posting!

The ultimate best repair for an S-crack is to understand the cause of S-cracks and recycle or toss the offender and start over.

If you fuss around trying to fix something that happened because you didn't understand the Dynamics of S-cracks you will continually have more S-Cracks!!!.

For starters when you open the ball of porcelain or clay, you must:
(1) compress the newly opened bottom by pressing your fingertips in several firm passes over the bottom.   Some folks use whatever rib fits their hand and diameter of the intended bottom for the compression effect.  Either/Or...you *must​*compress the bottom.

(2) don't throw with excessively watered throwing slip, or let throwing slip stand in bottom to soak into the Bottom clay or porcelain,   (Ok to throw "loose, but never sloppy")

(3) After throwing, as soon as you can flip the pot upside down without distortion do so because if bottom remains last to dry, the tension created between/against the dryer side walls will cause cracking. The bottom material has to give way to relieve the forces of tension.

(4) After trimming, again finish the drying by inverting the pot on a non-absorbent surface to allow the pot's bottom to keep up with the overall drying.
The inverted form creates a mini humid atmosphere which evens out the drying of the sides and especially the rims of bowl forms.
 On taller bowl forms I wrap a couple inches of plastic, or I paint wax resist on the rim areas to make sure the rims stay flexible while the other parts dry first.  Saves Bowls from cracked rims.

Some ones now will write in to say they don't wax rims and don't invert either......bla bla.   (So "bully for you" dude or dude-ett, happy ya got it workin for you.) How many $300.00 to $500.00 dollar Bowls did you make, sell, or lose last year???
I ain't talkin to you anyway!

Ken needs to have a road map for success and figure out his own viable shortcuts as he gains experience with his particular throwing body, technical methods and throwing style.

Misneach,

David Woof........................If it hurts so much...why are you still doing it???????
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________________________________
From: Clayart <clayart-bounces at lists.clayartworld.com> on behalf of Ken Chase <kchase235 at gmail.com>
Sent: Thursday, November 12, 2020 9:22 AM
To: clayart at lists.clayartworld.com <clayart at lists.clayartworld.com>
Subject: [Clayart] S crack remedy?

Hello:
Haven’t posted in a long time but read everything.
Trying porcelain and made one I really like but has a Large s crack at the bottom. Is there a pre bisque repair? Thanks

Sent from my iPad
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