Cold weather & drying clay

[heatherw724]

My studio is not heated and it has been in the 30's at night. I noticed my large bowl, that were drying, had S cracks.

I am familiar with this problem and think I should've dryed them slower but I was wondering if the cold weather excellerates the drying or has any effect on pots as far as cracking while drying.

I am also at high altitude so does that have any effect on drying greenware?

[Guest JBaymore]

The partial pressure of water vapor in the air affects how quickly more water molecules will evaporate off the surface of a given material. So the dryer the air surrounding a piece, the more rapidly liquid water in the clay will evaporate into the air. As the temperature goes UP, this accelerates that drying, and as the temperature goes down, this retards the drying.

 

Typically as the temperature goes down, the humidity drops. And high altitude exacerbates this situation. So this may be your issue. The air is getting REALLY dry.

So cold dryer air might be somewhat similar to warm damper air .

 

 

One thing that you have to watch out for is the wet clay that has already been formed into objects FREEZING. Wet pots (or sculptures) freezing will show cracking of the clay.... but not typically the S cracks you are describing.

 

And to make sure that this whole "frozen clay is useless" subject does not start up again...... if non-formed wet clay freezes... just thaw it out, wedge it up, and use it. It is fine.

 

best,

 

................john

[Pres]

The partial pressure of water vapor in the air affects how quickly more water molecules will evaporate off the surface of a given material. So the dryer the air surrounding a piece, the more rapidly liquid water in the clay will evaporate into the air. As the temperature goes UP, this accelerates that drying, and as the temperature goes down, this retards the drying.

 

Typically as the temperature goes down, the humidity drops. And high altitude exacerbates this situation. So this may be your issue. The air is getting REALLY dry.

So cold dryer air might be somewhat similar to warm damper air .

 

 

One thing that you have to watch out for is the wet clay that has already been formed into objects FREEZING. Wet pots (or sculptures) freezing will show cracking of the clay.... but not typically the S cracks you are describing.

 

And to make sure that this whole "frozen clay is useless" subject does not start up again...... if non-formed wet clay freezes... just thaw it out, wedge it up, and use it. It is fine.

 

best,

 

................john

 

 

 

John,

I actually prefer clay that has frozen over the Winter, thawed in the Spring or in the house in Winter. I find that the water that comes to the surface leaves a stiffer body if I cut off the outer edges. At the same time, If I want my clay wetter, just wedge it all up. I do like to recycle slop with the freezing/thawing method.

[macdoodle]

PRES, what is the freeze/ thaw method of recycling slop?

[macdoodle]

JOHN,

So formed objects always need to be kept above 32 degrees and even if it is cold if the air is below say 40% humidity? use plastic (or a humidifier?) for slower drying?

[Guest JBaymore]

JOHN,

So formed objects always need to be kept above 32 degrees and even if it is cold if the air is below say 40% humidity? use plastic (or a humidifier?) for slower drying?

 

 

If you let wet pots freeze, the water will form ice crystals... and start cracking the clay in the process of the expansion (ice takes up more volume than an equal amount of water). Most times you can see the cracks in the body if you catch the clay while it is still frozen. But sometimes it freezes at night and by the time you see it... the obvious ones APPEAR to have settled down as the ice crystals go back to being liquid water. But they are still there... to show up later.

 

Been there, done that, bought the T shirt .

 

 

And yeah... low huumidity is low humidity. So water "wants" to go from the liquid state to the vaporous state. Plastic is your friend. Or beter yet, a damp box.

 

On a related side note.... when working over in Japan I've worked with one particular clay that if you cover it with the usual plastic to retard drying like we frequently do here in the USA.... it ALWAYS cracks. BUT.. ..... if you simply cover it well with sheets of dry newspaper draped over the pieces, it retards the drying quite nicely and does NOT crack. My theory is that the tiny bit of moistrue that collects on the inside surface of the plastic then is re-absorbed in the contact areas by the dryer clay.... and that expsnsion of the clay where the water is re-absorbed is what does the damage.

 

 

best,

 

..............john