clay cracking. need a lil help

[Ryan_Gill_HuntPrimitive]

I am trying to figure some clay work out. I found a good clay deposit, very sticky stuff. brought it home and soaked it to get the aggregate to sink and poured the slip off the top and used the good, decently clean clay. I made a pair of pinch pots to learn from and plan to fire when dried out.  Three days have passed and as my pots are drying they are cracking...i figured this would be a problem....  I get a little water and apply to it and rub up some cream (like I would when I used to finish cement) and filled the cracks in.  I figured I should do this or add a little extra creamy clay to fill in the cracks as I go until it is totally dry.    I hope that is the right thing to do.....      any suggestions?  Is the cracking inevitable? or do I do just like I have been? or does it mean there is too much sand in my clay? or not enough???    any tips would be appreciated

[bubby]

sounds like it still had too much moister when you made it, but i'm just guessing, maybe iowabow will chime in he does lots of pottery

[sleek]

I have done a little clay work. I add sawdust to my mixture, and it takes a bit, like just shy of 1/3 dust. You can also use straw. It needs to be completely dry before firing. The dust/straw adds strength, and if fired moist, the water expands and can actually blow pieces off. warm it up slowly and evenly, cool it off the same. Let us know how things turn out... with pics

[KShip85]

I'm no master but I've worked a fair bit of pottery.  My first guess would be to echo drying slower.  How thick are the walls?  Another issue might be the clay isn't elastic enough.  Adding some bentonite would help with that issue.  I've not done a ton of primitive clay work but I would think principles carry over from more complex clay bodies to more simple ones.  How did these dry? Just open air or were they partially covered?  Nearly all my clay work was loosely covered with a plastic sack for a week or two before uncovering to dry out completely.


Kip

[Ryan_Gill_HuntPrimitive]

thanks guys. as of now only one is cracking....it was the first one I did and it isnt as nice, so maybe it was me varying the thickness too much....maybe not..the other could start at any minute! they have just been drying open air in the house since I did them. perhaps I should go ahead and throw something over the nice one to help prevent cracking.  I may try the say dust too. I heard about adding cattail fluff....same principal as the sawdust I suppose. I might try that next time.  I feel like I have so much to learn with pottery that is why I didn't want to start! but now that i have I am stuck and must master it or I wont be content...  the clay seemed pretty good. could just about tie it in a knot without it cracking or breaking...but i still think it could have been better

[Pat B]

You might need to add some sort of reinforcement like with concrete. Maybe something like chopped up straw or moss. Something that would burn out when fired but would hold it together until it dried out. This is a complete guess on my part. I don't really know! 

[PrimitiveTim]

Ooh is that that real bright orange clay like they've got up in Tallahassee area? 

[Ryan_Gill_HuntPrimitive]

nope, just ol grey colored clay. I could probably get some of that orange clay. there is a deposit just up the road a ways...  figure it's any good?  I don't remember it being near as sticky.. but I guess once it is concentrated down it would be...hmm

[Ryan_Gill_HuntPrimitive]

second one has a crack this morning    I covered it with a damp paper towel.  guess i will try some plant fibers next time. I hate making something just to have it ruin a couple days later.  I guess if nothing else I can fire them and grind them up for temper in the next pots

[Ryan_Gill_HuntPrimitive]

I watched a bunch of youtube videos on firing the pots....  no one gives and idea as to how long to fire them.   Is it a 1 hour ordeal or a 6 hour ordeal like cooking chert?  I have the chert cooking in a fire pretty well figured out..im tempted to try the pots the same way...I can't imagine the pots don't blow up in the open fire

[Ryan_Gill_HuntPrimitive]

well covering with a damp papertowel proved to be dumb.....now they are mushy again....15 minutes and they are ruined...guess I will soak them down again and start over. I'll add some saw dust or something of the like

[richardzane]

pottery with native clays is what i do for a living ,now for 30 years.

there is alot of things that could cause cracking.
--it might be TOO much shrinkage(too much bentonite) not enough temper (crushed rock ,sherds,shale,shell, or sand)
or --too much water added after the pot begins to dry...will crack a pot
or --slumping...when clay sags it tends to split  (where are your cracks showing?) from the rim,  the base?

If you want to work outside you'll like to use a good cattail mix.
this works for me and has for my students too:
mix some thick clay slip ,about 2.5 gallons, then push into the slip, the fluff from the heads of three to four cattails.
keep pushing it under...it wants to float... once its soaked - saturated . smear the clay out on a piece of formica (or lay it out on a cloth on a concrete surface to dry.)
you can also hang it in a cloth bundle from a tree to dry to the plastic stage.
this mix is NOT The clay you will build a pot with...this is only the starter mix. keep it stored in plastic( or in a cave) out of sunlight (it will sprout!)
whrn you are ready to make a pot take a good pinch of the cattail mix and add it into your clay,wedge it in good
till when you pull pieces of clay apart you see the fibers all through it.

Find a round object (ancients would use an old cooking pot.) you can use a bowling ball or a round plastic light fixture to get your first cooking pot from.
---pad out a fat tortilla of clay and coat it thickly with fine wood ash. I use a paint brush to spread it on the clay tortilla.
plop that ash side down on your rounded form and with a wood paddle begin to paddle it over the rounded form evenly.
CHECK IT OFTEN so its not sticking...if its sticking even a little, flip the bowl form into your palm and add more wood ash.

eventually you will have the rounded base of your pot made. the cattail fuzz will keep the pot from cracking and you are working with gravity
when you paddle down over a form. let it stiffen up a bit before you remove it from the form.
to remove it from the form flip the form upside down(pot and all)  and let the pot slide away into your hand.
then set it in a bowl of sand or a dry mud bowl with a rounded interior to hold it.

this is just the first stage but i think you'll like cattail fuzz clay, you can paddle it very thin, which is what you want for safe firings.


 

[richardzane]

here's some visual aides for paddling..this is clay with cattail fuzz and crushed shale temper
and here I'm working outside with a breeze blowing

[BryanR]

Twisted,

I would say you need to add grog - 10 to 20 percent of he piece of clay your working with.  Grog reduces the shrinkage that you're seeing as the pieces dry.  i buy mine online, not very expensive.  Comes in several types of material.  Go for cheapest price.

Firing is easy, takes about an hour hour/half in my metal fire pit.  Build a nice tall fire structure to support the burning wood so large logs don't fall and break your pottery.  Keep the fire going for about an hour, then let the coals cool overnight.  If you get a ringing sound plucking your finished pieces, you are doing it right.

No harm done so far, as you can always redo the unfired clay by adding a bit of water.

I also like to heat my pieces in the oven the night before I fire pottery just to make sure all the moisture is out.  About an hour at 200 degrees.  This isn't really necessary if you've air dried for a week or more.  I just hate losing a piece in the pit.

My last round, 5 of 7 pieces made it through. 

[richardzane]

 primitive firing  (more than one way to skin a cat- but this is what works for us)

the day before the firing build a fire on the area you have chosen to fire your pots keep it going all day to assure the ground is dry.
if there is any moisture from the earth (or in the vessels) , the steam will crack your pots or cause them to explode in the stage before red heat.

the firing day a non-windy morning is best, build a BIG fire on the spot and let it burn down to coals. put dried pots you are going to fire around the coal bed
and adjust them occasionally with leather gloves on..
when they are FULLY dry, after an hour or so...they will actually have a ring to them when they are thumped.

lay some broken sherd(everyone has broken sherds!) over the coals and place the pots face down over those sherds.
take your time, this will further dry them. take a mixture of dry wood ash and wood chips and cover the pots entirely.
there will be some smoke. once the wood ash is packed into a nice rounded hill over the pots(might take a wheelbarrow full of the mix)
then you can begin laying dry thin split wood right on the mound of ash, i never use any wood thick enough to crush a pot if it falls.
the wood might ignite on its own if not, start small fires all around the mound...and let her go.
the ash mound acts as a pottery protector from flame. the flame will be trying to find your pots and look for any weaknesses
or air bubbles.
though it can be useful as windbreak or a covering you really don't need any metal to do a primitive firing.
you will be adding pieces of split wood as the fire burns for a good hour, keep covered with coals and you may catch glimpses of glowing pots
you can either let the fire die slowly on its own, or t be safe, you can shovel DRY sand or dried earth over the mound and let it cool slowly.
open it carefully the next day. rub vegetable oil on the warm pots, just like you season a new cast iron skillet.
the mixture of ash and wood chips will give you the fireclouds and coloration typical in primitive firings.

these pots can be cooked in. rounded bottom pots are the safest form for cooking  (use three stones for leveling it)
but to prevent cracking a cook pot, make sure the stew or liquid you are cooking or boiling is brimming full,  if you have a good blaze going.