[Ray Bright]

I'm trying to run two batches of greenware, one weeks dry the other one week dry, and wonder if I can somehow dry them both a little more before 1-firing them? I've heard, only in passing, about "candling" which I assume means a slow low heat cooking of the greenware to dry it out. Is that what candling is? And, is that a good way to insure my greenware is sufficiently dry? Is there a way to 'know' the clay is dry enough for cone 05?

R

[Chris Campbell]

A good rule of thumb is that if the piece feels cool when you touch it to your cheek, it is still wet.

Candling is slow heating kept below the boiling point of water ... About 200F or the very lowest setting with the lid propped open to let moisture escape.

[Ray Bright]

Candling is slow heating kept below the boiling point of water ... About 200F or the very lowest setting with the lid propped open to let moisture escape.
[/quote]

Does candling work? I'm a little scared, as my last firing had one item blow up and ruin everything else in the kiln. Think that one item was wetter than the rest.

[Chris Campbell]

I am not a great believer in rushing clay but sometimes you just gotta give it a push when deadlines are looming or the rain just will not stop. This is always done with a degree of risk. Thinner pieces are more forgiving and easier to judge but thick walls and sculpture can be deceptive as to whether they are dry enough. My teachers told me to hold a mirror near the cracked lid during the candling and if there was any fogging it was too early to turn up the heat. You can candle as long as you need to ... just stay below the boiling point.

[neilestrick]

If it's a manual kiln, just put the bottom element on Low and crack the lid and inch. Let it run till you're confident everything is dry, anywhere from 4-12 hours. I don't fully trust the mirror and fog trick, because there could still be one piece in there that's not totally dry, but not producing enough water vapor to fog the mirror. It never hurts to just candle overnight before each firing.

[yedrow]

You could also make a tent around your work, in a metal frame if you have it. Use some cheap thin visqueen for your tent. Put a small electric heater at the bottom and turn it on. The thing will puff up and move the water right out of your work, protected by a blanket of humidity.

Joel.

[Jime]

if it's just a few pieces that you're more worried about, you could treat them separately.
I have put a piece on my pottery wheel to turn while I get a hair drier on it, or if your oven does low temperatures consistently, you can put it in there


here's a story that I just have to share, as part of the pottery bloopers.
I made my partner 4 matching beer steins for Christmas. They were incredibly elaborate, my first real attempt at sgraffito, and I spent a ridiculous number of hours on them. Once I finished carving, I decided to speed them up just a little bit, and I put them in the oven on low. I checked on them every once in a while and they were doing great. I had to leave the house on a quick errand, and I decided to be responsible and turn the oven all the way off while I was gone.

her comes the fun part.

that oven knob was completely misleading, and I ended up turning it to full blast broil instead of off!!
I ended up coming back to the house with my partner, and I shooed him away so I could take them out of the oven and keep the surprise going...
they had EXPLODED. as only pottery can. every one of them had burst into shards and crumbs.
I cried and cried and cried and showed him the pieces, and told him that under no circumstances was I remaking them and that he was getting NO Christmas present. There were very bitter tears that night.

and then, the next morning, I got up again and started remaking them. he was VERY surprised that christmas

so, if you use the oven, make sure it says LOW, not BROIL

[oldlady]

[so, if you use the oven, make sure it says LOW, not BROIL
[/quote]


i use the oven in my kitchen often. it has a setting of 170 degrees. if i put wet things in it i set the timer for 15 minutes and turn off the heat after it rings. if i leave the heat on, my flat pieces arch their backs and warp horribly.

after quite some time doing something else and once everything looks and feels dry, i put the pieces in the kiln and set a preheat of 10 minutes. since the kiln takes a looonng time to get to the preheat temp, a 10 minute hold is a lot. this only works if you have the same kind of L&L kiln that i have.

[Pres]

Ray Bright, on 22 October 2012 - 06:45 AM, said:

I'm trying to run two batches of greenware, one weeks dry the other one week dry, and wonder if I can somehow dry them both a little more before 1-firing them? I've heard, only in passing, about "candling" which I assume means a slow low heat cooking of the greenware to dry it out. Is that what candling is? And, is that a good way to insure my greenware is sufficiently dry? Is there a way to 'know' the clay is dry enough for cone 05?

R

Like many of the others have said here-take your time. Best to let the clay dry thoroughly, but if in a hurry, after a week most should be good with and overnight candling. I often do this with work that may be a little iffy with moisture, leave the lid cracked or to the side part way and fire bottom switch on low. Next morning I put the lid on and remove the top site plug. For me, just placing my hand up to the hole 30 minutes later will let me feel if the air is either dry or wet. Then if dry I continue my normal firing for bisque. If wet, I leave the kiln on low until the air is dry. then fire/

[ClayByMck]

I must be lucky. I fire leather hard clay all the time with no issues. This is my favorite cone 04 schedule. Its in the kiln for a while but its not sitting on a shelf drying for weeks on end.

90° F per hour up to 185° F
hold at 185° F for 4 hours
100° F per hour up to 600° F
200° F per hour up to 1922° F
Let the kiln cool on its own

[OffCenter]

ClayByMck, on 02 December 2012 - 09:22 PM, said:

I must be lucky. I fire leather hard clay all the time with no issues. This is my favorite cone 04 schedule. Its in the kiln for a while but its not sitting on a shelf drying for weeks on end.

90° F per hour up to 185° F
hold at 185° F for 4 hours
100° F per hour up to 600° F
200° F per hour up to 1922° F
Let the kiln cool on its own

You're not firing leather hard clay. You're candeling leather hard clay then firing dry clay. Unless your clay has lots of impurities in it or is extra thick there is no reason not to turn the kiln on high after getting 20 or so degrees (just to be sure) past boiling point.

Jim

[Pres]

Pres, on 30 October 2012 - 10:34 PM, said:

Ray Bright, on 22 October 2012 - 06:45 AM, said:

I'm trying to run two batches of greenware, one weeks dry the other one week dry, and wonder if I can somehow dry them both a little more before 1-firing them? I've heard, only in passing, about "candling" which I assume means a slow low heat cooking of the greenware to dry it out. Is that what candling is? And, is that a good way to insure my greenware is sufficiently dry? Is there a way to 'know' the clay is dry enough for cone 05?

R

Like many of the others have said here-take your time. Best to let the clay dry thoroughly, but if in a hurry, after a week most should be good with and overnight candling. I often do this with work that may be a little iffy with moisture, leave the lid cracked or to the side part way and fire bottom switch on low. Next morning I put the lid on and remove the top site plug. For me, just placing my hand up to the hole 30 minutes later will let me feel if the air is either dry or wet. Then if dry I continue my normal firing for bisque. If wet, I leave the kiln on low until the air is dry. then fire/

Just a side here, candling is often known as watersmoking, or pre-firing. All the same, but the slow time in the beginning will remove any mechanical water still in the clay and atmospheric water still in the clay. Remember that there is also the chemical water that will come out from 200 to 1000F. Main reason for your shrinkage of the piece.

[Marcia Selsor]

you can check to see if any moisture is leaving the kiln by holding a glass jar inverted near the cracked opening of the lid. If the jar fills with moisture, don't shut the lid yet.
You can also hold a mirror or a piece of glass near there too. Steam tells you what you need to know. I used this system on gas kilns as well as electrics. I just put the jar in front of the top peephole.
Marcia

[Benzine]

Pres, on 03 December 2012 - 08:21 AM, said:

Pres, on 30 October 2012 - 10:34 PM, said:

Ray Bright, on 22 October 2012 - 06:45 AM, said:

I'm trying to run two batches of greenware, one weeks dry the other one week dry, and wonder if I can somehow dry them both a little more before 1-firing them? I've heard, only in passing, about "candling" which I assume means a slow low heat cooking of the greenware to dry it out. Is that what candling is? And, is that a good way to insure my greenware is sufficiently dry? Is there a way to 'know' the clay is dry enough for cone 05?

R

Like many of the others have said here-take your time. Best to let the clay dry thoroughly, but if in a hurry, after a week most should be good with and overnight candling. I often do this with work that may be a little iffy with moisture, leave the lid cracked or to the side part way and fire bottom switch on low. Next morning I put the lid on and remove the top site plug. For me, just placing my hand up to the hole 30 minutes later will let me feel if the air is either dry or wet. Then if dry I continue my normal firing for bisque. If wet, I leave the kiln on low until the air is dry. then fire/

Just a side here, candling is often known as watersmoking, or pre-firing. All the same, but the slow time in the beginning will remove any mechanical water still in the clay and atmospheric water still in the clay. Remember that there is also the chemical water that will come out from 200 to 1000F. Main reason for your shrinkage of the piece.

I had never heard the term "Watersmoking" until recently. I have always just known it as "Candling".

But now that I do know it, I'm thinking of using the term, as the title to my first solo album. I don't perform music at all, but if I do so later, and make an album, I'm definitely going with that title.

[BarefootPottery]

Here are two great firing schedules that might help:


Damp ware bisque profile

This profile is used for pots that are past leather hard butare not bone dry
90° F per hour up to 185° F
hold at 185° F for 4 hours
100° F per hour up to 600° F
200° F per hour up to 1922° F
Let the kiln cool on its own



Thick as a brick bisque profile

This profile is used for sculptures or kid made wares thatare thick as a brick and would explode from the steam in a normal firing
90° F per hour up to 185° F
hold at 185° F for 8 hours
100° F per hour up to 600° F
200° F per hour up to 1922° F
Let the kiln cool on its own.

I forget where they came from, but they have never failed.

[Diane Puckett]

For pieces that are not quite dry or have thick bottoms, it is a good idea to use some small stilts to raise the bottom of the pot off the bottom of the kiln shelf to give an outlet for any steam released from the bottom.

[OffCenter]

BarefootPottery, on 03 December 2012 - 11:18 PM, said:

Here are two great firing schedules that might help:


Damp ware bisque profile

This profile is used for pots that are past leather hard butare not bone dry
90° F per hour up to 185° F
hold at 185° F for 4 hours
100° F per hour up to 600° F
200° F per hour up to 1922° F
Let the kiln cool on its own



Thick as a brick bisque profile

This profile is used for sculptures or kid made wares thatare thick as a brick and would explode from the steam in a normal firing
90° F per hour up to 185° F
hold at 185° F for 8 hours
100° F per hour up to 600° F
200° F per hour up to 1922° F
Let the kiln cool on its own.

I forget where they came from, but they have never failed.

Your first schedule has already been posted in this thread. Both are candeling added to a bisque firing and both are overkill.

Jim

[Wahine]

My studio is in my house, which I keep very cool, summer and winter. I have trouble with stuff drying too fast. If I leave a mug out uncovered, overnight, it is completly dry. That cool to the touch trick to check for dampness? What if its 55 degrees Fahn? My stuff always feels cool. I have to work to keep stuff damp if I want to work on it multiple days.



-chantay