S- Cracks

[glazenerd]

It is not about pots, how long they sit: or how you wedge it. Just simply a study on the effects of sodium in clay. Now I have to back up to the 30-60 day period and check for crystallization of the sodium. More interested in what makers do to overcome the effects of sodium. I think perhaps in the short term more problematic than the sodium itself. Sodium in porcelain is easy to spot: because the clay is short. Rapid drying seems to be a close second.

 

I have a working theory on why it does not happen to walls: will present that when I am done testing. The Romans used arcs to build bridges, coliseums and houses; because it is the strongest of all shapes. It distributes weight and stresses evenly across its radius. That is the mechanics, but I do believe S cracks are based in formulation. Testing will tell.

 

Nerd

[neilestrick]

It is not about pots, how long they sit: or how you wedge it. 

 

Nerd

 

If it's about S cracks, then it's totally about pots.  I guess I'm just wondering if the effects of the sodium really matter if the working of the clay negates those effects.

 

Drying fast is not an issue. Drying evenly is. I dry my porcelain pots in the kiln quite often, with no ill effects. 

[Mark C.]

A forum friend and I have been discussing the cause/s of s cracks. I would like to poll the forum for some additional information.

 

1 do you experience this problem more with stoneware or porcelain?

2. If stoneware, is the body white, tan, grey, or dark?

3. If porcelain, do you know if sodium was used as the primary flux?

4. Does it occur more during hot weather?

5. Have you noticed any differences in outcome if the base is thick or thin?

 

Feel free to share thoughts, opinions, or other information. Thanks for the input.

 

Tom

!-I use so little stoneware -only for salt pots-I do not experience this in my cone 10 Dave's porcelain from Laguna-no s crack issues

2-White stonewares are classic cracking and uneven drying bodies especially B-mix

3-I think that is used more in a lower temp flux for say cone 6 bodies-they need to flux out so nepsy is used more often-I'm not a cone 6 person

4-no hot weather drys my work as faster and I like it that way

5-I never have thick bases-cracking can occur more on thicker uneven pot walls or bottoms-usually beginner issues and to much water left inside

6-Neil summed up cracking very well

7-S- cracks are a non issue with me

8- S-cracks most likely are a combination of poor clay bodies along with poor forming skills-I do not think you can separate them that easily .

Take b-mix as an example(cone 10 body)-its greasy wet sticky -super uneven drying-loves to crack as drying is a challenge to even it out-yes it has legs (throws well) but the drawbacks are outweigh the positives at least for me.Many beginners like it as it throws well but the cracking drives them nuts.

9-thats my info for the poll

[Mark C.]

I tend to dry my pots as fast as they can-Like today I will throw them and put them in sun until I can trim them then put them back in sun and by end of day pots are bone dry depending on forms-handled pots need to be babied more.

S-cracks do not show from this fast dry process-they show from poorly thrown processes more like lack of compression.

[glazenerd]

Mark:

You use mostly porcelain, and s- cracks are mostly associated with stoneware. I do agree compression is a key factor in this issue, but not the only issue. Sodium has been used in porcelain for several decades, it is becoming more common place in stoneware. The big distinction between porcelain and stoneware is ball clay. Ball clay holds water much differently than kaolin; so that difference alone changes drying times and drying properties. There is a lot of chemistry involved as well, but will sit that aside. Not saying sodium is causing s- cracks, just exploring if it adds to the problem. Which I am fairly certain that it does in stoneware, because of the chemistry.

Nerd