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Importance Of Drying Slowly


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I am trying to understand what slow drying is and why it is important. is it just to avoid cracks? what happens when you fast dry? i understand some technical stuff like clay platelets and how they move.

 

i am told some items should be really slow dried like plates, but others you can dry less slowly like bowls. if that is so why is that?

 

i will be in 3rd semester community college class. i notice advanced students who are also TAs still have cracks in their bowls. apart from compression and or too much water used to throw could improper drying play a role for the cracks?

 

i have been both throwing and hand building bowls (both pinch pots and slabs). i prefer the uneven feel so with the hand built pieces since there is no need for trimming (i build them in one sitting), maybe put slip on them and then air dry them. depending on the weather they are bone dry within a day or max two. usually the school candles especially if there are sculptural pieces going into the same kiln. i have not had any problems with cracking.

 

does slow drying apply both to thrown and hand built pieces equally? in my classes from two different teachers the wheel throwing teacher emphasized drying more than the other teacher which was a handbuilding class (small handbuilt pieces which were done in one sitting). i have even taken a handbuilt bowl at leatherhard stage put it in the oven and baked it for 8 hours at the lowest temperature and it then went into the kiln and i have had no problems.

 

to understand drying i've played with clay thickness and molds. thin clay 3/8" on the outside of the mold left for 3 hours on the plaster of paris mold without cover and then air dried without cover and the cracks appeared during glaze fire. same experiment with half inch thickness of clay and no cracks. i was told i should have covered them and slowly dried them before putting them in the kiln. 

 

what confuses more is i have watched youtube videos of korean production potters who throw bowls for an hour, set it out to dry in the sun for an hour and then throw for an hour and then trim the ones that they had put out in the sun. i am guessing its high fire clay as they wood fire, but does that make a difference? of course climate plays an important part - tropical wet heat instead of dry.

 

is there a different philosophy towards drying between the east and the west?

 

i have been scouring websites and books trying to understanding the process of drying but have not come across any so far. if you have any suggestions i'd welcome them

 

B mix clay 

Bisque fire ^04

Glaze/2nd fire ^5

 

 

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The main thing cracks occur from is uneven drying. When the particles are drying they are shrinking, when the shrinking occurs uneven, cracks happen. So that is why people cover pots to help the clay dry slower and evenly. 

 

There is a big difference in clays and cracks. Some clays you can flood the pot with water and throw the entire time with a pool of water in the bottom and it wont matter a bit, others like to be thrown dry. Some clays require more alignment of the clay(sometimes called compression). It really is up to you to figure out what your clay desires. If you have really good throwing skills and trimming skills then your cracks will decrease drastically. 

 

I am sure others will chime in, but as the man says, "it just depends". Find what works for your clay and stick with it. 

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I agree, its not the speed but the eveness of the dry out. If you are there to baby sit your pot while it dries then you can dry it faster moving out of drafts and turning it so the sun hits it evenly. I don't have that kind of time so my pots get a plastic bag over them to slow the drying and make an uneven dryout less likely.

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I often attach handles and put the mugs into the kiln to dry quickly. If the pot is even, and the drying occurs evenly, you can dry them as fast as you want. Bowls and plates d o not dry evenly. Vertical forms do better.

 

Neil,

What clay are you using? I just posted a comment about the tempermental nature of B-Mix and that no matter what I do, the handles fall off mugs. I've given up throwing mugs with it,

Nancy

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Preeta, I'm impressed with your experiments! It's really the best/only way to determine what your clay will do in your environment.

I wonder if the Korean potters put their pots in the sun in an area that was sheltered from breezes. They surely know their materials' limitations very well.

Your curiosity will lead you to discovery - best of luck!

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Hi all,

 

This question may fall into this drying topic/

 

I recently threw a large garden planter. It was dried outside. The weather is cooler these day, but the pot was outside exposed to air and medium heat (not in sunlight).  I candled it at 80 deg C for 6 hours.  During the bisque which I fired to 960 everything was fine. I manually shut down when the cone was in the correct position.  However 10 minutes or so later when the bung was removed just to check. The one shelf had toppled.  Later when the kiln was able to be opened I found that this pot had exploded.  I can understand if the pot had been subjected to a fast ramp and also not candled, but if it was too wet surely it would have "exploded" at a temp lower than 500 as super heated steam occurs at around 375.

 

I would really like to understand what happened as I have to replace the piece and I don't want the same thing to happen.

 

Thanks

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Hi all,

 

This question may fall into this drying topic/

 

I recently threw a large garden planter. It was dried outside. The weather is cooler these day, but the pot was outside exposed to air and medium heat (not in sunlight).  I candled it at 80 deg C for 6 hours.  During the bisque which I fired to 960 everything was fine. I manually shut down when the cone was in the correct position.  However 10 minutes or so later when the bung was removed just to check. The one shelf had toppled.  Later when the kiln was able to be opened I found that this pot had exploded.  I can understand if the pot had been subjected to a fast ramp and also not candled, but if it was too wet surely it would have "exploded" at a temp lower than 500 as super heated steam occurs at around 375.

 

I would really like to understand what happened as I have to replace the piece and I don't want the same thing to happen.

 

Thanks

Your pot was still wet inside. Was it thick walled?Large pots need to get dried out longer than small thinner ones. A slower ramp may help this.

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I am trying to understand what slow drying is and why it is important. is it just to avoid cracks? what happens when you fast dry? i understand some technical stuff like clay platelets and how they move.

 

i am told some items should be really slow dried like plates, but others you can dry less slowly like bowls. if that is so why is that?

 

i will be in 3rd semester community college class. i notice advanced students who are also TAs still have cracks in their bowls. apart from compression and or too much water used to throw could improper drying play a role for the cracks?

 

i have been both throwing and hand building bowls (both pinch pots and slabs). i prefer the uneven feel so with the hand built pieces since there is no need for trimming (i build them in one sitting), maybe put slip on them and then air dry them. depending on the weather they are bone dry within a day or max two. usually the school candles especially if there are sculptural pieces going into the same kiln. i have not had any problems with cracking.

 

does slow drying apply both to thrown and hand built pieces equally? in my classes from two different teachers the wheel throwing teacher emphasized drying more than the other teacher which was a handbuilding class (small handbuilt pieces which were done in one sitting). i have even taken a handbuilt bowl at leatherhard stage put it in the oven and baked it for 8 hours at the lowest temperature and it then went into the kiln and i have had no problems.

 

to understand drying i've played with clay thickness and molds. thin clay 3/8" on the outside of the mold left for 3 hours on the plaster of paris mold without cover and then air dried without cover and the cracks appeared during glaze fire. same experiment with half inch thickness of clay and no cracks. i was told i should have covered them and slowly dried them before putting them in the kiln. 

 

what confuses more is i have watched youtube videos of korean production potters who throw bowls for an hour, set it out to dry in the sun for an hour and then throw for an hour and then trim the ones that they had put out in the sun. i am guessing its high fire clay as they wood fire, but does that make a difference? of course climate plays an important part - tropical wet heat instead of dry.

 

is there a different philosophy towards drying between the east and the west?

 

i have been scouring websites and books trying to understanding the process of drying but have not come across any so far. if you have any suggestions i'd welcome them

 

B mix clay 

Bisque fire ^04

Glaze/2nd fire ^5

My high fire porcelain mugs are thrown put in the sun until dry enough to pop off plaster bats (usually 2-3 hours ) and then handled and covered inside for 1 night then dried for a day.

I can put them in the kiln after handling if they are even in dampness but small cracks can occur at handle unless they are just right with same moisture . I can sun dry them that day if needed soon as well.

The trick is even throwing and wet handles all the same moisture .B mix is no good for this

I am a production potter so speed is a key element-no babying of pots except teapots.

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Joel thank you so much for that link. that was VERY helpful.

 

ok so now i understand. its about uneven drying and not speed.

 

thanks Rae for your encouraging words. the korean pottery video i saw on youtube and i could not tell if there was a breeze or not. but that IS a thought. 

 

neil that is interesting. have had no problems with cylinder forms but yes have had issues with bowls and plates. 

 

Mark one day i aim to be a production potter. so i am trying to keep speed in mind eventually. what i have found with cups is throwing day one and then covering it for 24 hours. then i come back and first pull the handles. while the handles are drying on wood without cover i trim the cups and then attach the handles. usually about 45 mins between pulling handle and attaching handle. then they are air dried. gets into the kiln that evening or next day. so far i have never had any problems. 

 

nancy off to check your thread. 

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Hi all,

 

This question may fall into this drying topic/

 

I recently threw a large garden planter. It was dried outside. The weather is cooler these day, but the pot was outside exposed to air and medium heat (not in sunlight). I candled it at 80 deg C for 6 hours. During the bisque which I fired to 960 everything was fine. I manually shut down when the cone was in the correct position. However 10 minutes or so later when the bung was removed just to check. The one shelf had toppled. Later when the kiln was able to be opened I found that this pot had exploded. I can understand if the pot had been subjected to a fast ramp and also not candled, but if it was too wet surely it would have "exploded" at a temp lower than 500 as super heated steam occurs at around 375.

 

I would really like to understand what happened as I have to replace the piece and I don't want the same thing to happen.

 

Thanks

AndreaB, as Mark C says, thickness is probably a factor. Stresses to thick/thin areas can happen even without steam. Others may correct me, but I don't think all the free water leaves clay until Quartz Inversion (1050 deg? or so). If the body just separated from the base and toppled, it's a thick/thin problem. If the base turned into a pile of flat shards, probably moisture.

 

Preeta, drying your pots upside down, as soon as the rim can take it, makes it more certain to dry completely. For fragile-rimmed pieces, I put them on a rack made of flat strips (actually, it's a recycled baby crib side) that allows air to circulate beneath them. The "cheek test" is pretty reliable for determining dryness - put the bottom of the piece against your cheek. If it feels even remotely cool, it's not dry enough to fire.

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preeta, have you said what kind of surface you use when you take your pots off the wheel and put them down?  is it drywall so the bottom can have moisture wicked out?   turning them upside down as soon as they can take it is very important if you do not use drywall.  putting them on a wire rack with air coming up through the rack is also helpful. 

 

how do you trim your cups?  the simple rolling the base on a flat surface and tapping the center should be enough for most mugs.  if you are planning to be a production potter, that is a skill you might want to practice.

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For me the b-mix would be the issue as it dries so uneven-lips are dry and bottom is wet.B mix is notorious for cracking

I use plaster bats for my porcelain production as it dries the bottoms as fast as the tops dry as soon as I can release them from the I gather them on larger bats

(many overlook this point as to why to use plaster) cover them until  ready to handle-usually after lunch. Then  extrude the handles and handle them then cover for the night.Mugs get handled same day as produced 99% of time.

Maybe try a stone ware clay as its more forgiving.

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aaargh. second time typing. my post disappeared.

 

rae i do turn them over the moment the rims are ready, i usually put fragile rims on a sponge but the slats is a good idea. for sure better circulation. thanks to our kind lab tech i do know about the cheek method. she is very thorough with her job so she never puts anything in the kiln that is wet. when she does put in uneven pieces she candles overnight.

 

oldlady on a wooden board. i dont think we have dry wall in school. 

 

i do roll and tap for trimming. i learnt that from youtube. the first school i went to hand griffin grips and encouraged that. but i looked on youtube and never used the griffin grip. in my present school i dont have access to one so i roll and tap.

 

Mark at this moment i am researching local options to replace the Bmix. for sure i will not throw plates with bmix (i might just to see the difference). in our school people have so much cracking with plates. and most of them use bmix.  so far i have not had any problems with bmix - neither with my cylinders, cups or bowls. i had no idea about bmix till i came to this board. 

 

mark how thin do you throw your cups? we dont have any plaster bats in school. our school studio is open max 5 hours. the winter sun was not hot enough to dry them evenly. after i put them in the sun face down and thought they were ready (maybe 3 hours) i realized they were hard outside but soft inside making it difficult to trim. it was easier to leave them overnight and do the handles first thing next day.

 

but oh ho ho. not proficient enough to go anywhere near throwing with porcelain yet.

 

would a plaster bat be preferable for throwing plates to help with drying? 

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Plaster bats are not for school situations they break to easy

Sac is a hot climate in the spring and fall so drying should be easy and fast compared to our redwood coast.

I tend to throw things on the this side and making efforts always to thicken them so they last longer in daily use. Mugs -sponge holders spoon rests-vases-most pitchers are all No trimmers. 

Sine you are just starting I suggest a better clay body than b-mix a light colored stoneware will throw as well and not crack a much .

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Ditch the B-Mix. It's not a good clay unless you have a studio that you can climate control or you have the time and ability to do exactly what you want with it, and why go through all this trouble. I used it for a while when I was beginning, it is just a super frustrating clay that is too fine grained. Get a nice buff or white stoneware.

 

If you can post what suppliers offer in your area we can give you some great choices. If you have a highwater supplier in your area try little loafers, it is fantastic and the best white cone 6 stoneware I have ever thrown and I have tried a lot of clays over the last 2 years.

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I agree with Joseph F get a hold of a bag of little Loafers from Highwater Clay. It's wonderful for throwing as well as hand building. It's the only clay I use.

 

T

I think little loafers is not at all out west here. You east coasters are more in the loafer zone.

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Yea I don't know where the OP is located! I imagine shipping clay coast to coast is a bit expensive for the price they get for it. Surely there is something better than B-Mix in the west coast? 

 

EDIT: NM, I see her location under her username. California. So yea, I doubt you get any Loafers! Maybe someone who works in cone 6 white stoneware can recommend some west coast clays.

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Laguna's, (west coast division), Dover White is one of the first clays I used, I found it very forgiving for attachments, little warping etc. But getting glazes to fit was a bit tricky, they tend to craze unless low expansion. Their midrange Half and Half (half porcelain, half stoneware) is okay, not as white as Dover though.  

 

I don't think there is 1 perfect clay for making all wares, might have to use a different one for platters or slabs than you do for mugs and smaller stuff.

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There can't be enough said about allowing things to dry slow! And that goes with a good decent clay, which B Mix isn't. Immho :)

I told once of a potter acquaintance in Asheville, NC whose niche is 34 inch platters. She makes several platters and fills a sealed metal cabinet with them, and marks the calendar. When the cabinets are open in THIRTY days they are leather hard, and she proceeds to finish them with incising and trailing. I think there be some sprigging in there too. HGTV did a video of her but I haven't seen it in years..(Nine hours filming for 5 minutes video)

 

Water expands 1,700 its volumn when it turns to steam around 200 - 212 degrees F.

I am not sure where the 375 temps come from, but that's way too high for drying out pottery. Sculpture is another animal all together. At the college, it wasn't too uncommon to have the kiln soak over the weekend for sculpture, then bisque fire Monday. (The kiln was a 40 cf Baileys gas kiln)

 

You'll learn what you can and can't do with certain clays and forms. I'd make certain forms from different clays and see how they do. Smaller items might not need grog, but larger items might need a clay with grog, to keep from cracking.

 

So, types of clay, form, techniques, experience mean everything! Don't email the Korean master potters to tell them they're doing pottery all wrong! :)

 

Have fun, research, watch more of the YouTube, and keep notes. If you find a good pottery book, check out the bibliography since there's always a chance there's a better one listed. Use the colleges inner-library system to look over a book before you buy it.

See ya,

Alabama

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there are two main suppliers where i am. if i need anything else i'll have to travel a few miles. 

 

Industrial Mineral Company gets its clay locally and their factory is right here, IMCO. i have not tried any of their clays. they have Great White and navajo wheel red. and some darks too. 

 

http://clayimco.com/mid-range-clays.html

 

I can only get mid range ^5 Laguna brand at the other place. i am hoping they will have more choices in store. they are very helpful and knowledgeable so i can go in and talk to them.

 

http://www.ceramicsuppliesnow.com/index.php?cPath=308_309_311&from1=pdm

 

i know students here at school just use a high fire clay just to get what they want. i want to avoid that unless i am forced to.   

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 IMCO's Geostone cone 10 clay is really nice!!!! I used that for quite a while when I high fired. If they make a midrange version of that that it might be worth trying. Less crap in IMCO's clays than Laguna's (like bits of metal, wood, and unblended chunks)

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