Throwing big

[CactusPots]

To get past the limitation of centering and opening a single piece of clay, what's your preferred method, assuming you do this.

Throwing 2 or more sections and joining before final pulling and shaping

Adding coils to a thrown base and final pulling and shaping.

Is there a better way?   Or do you just stop at your limitation?

[liambesaw]

I like throwing separate pieces and joining, but even that is severely limiting.  You can go high but it's difficult to go wide.  If you want wide and high, coilings the ticket.

This bird bath was thrown in 3 pieces and joined.  

[oldlady]

cactus,  how many big pots have you made?   is it enough so you have developed skill making them before getting to the point of firing any?    the photos show excessive thickness for any size pot.

try a few more that you cut through to see the wall and floor thickness before putting one in the kiln.

this reply was to the other thread and i don't know how to move it.

[Mark C.]

When I made big pots I threw them in sections and joined them-up to three at a time. (never did the coil deal). Measured the diameters and scored and slipped them together and then threw them more as one on the wheel.. Made thicker and then thrown thinner .In terms of firing I always used some sort of slide material in the firing so they did not grab. I have poosted all this before. I have some very small ball bearing size high fired porcealain  balls that came from Coors ceramics in midwest-They where a gift from another potter in the 80's who made large works. Coor's reacently told me they will not sell small amounts  of them (they are made in exact sizes and are used in technical uses. Coils work fine waster slabs as well.

In terms off firing bowls upside down it works for small ceral bowls  and meduim size ones only-nothing large.

[neilestrick]

These are some porcelain planters I did a few years back. They're about 45 pounds each. To give you an idea of the size, they are sitting on 13in bats. The base is thrown as a 7 pound disc that covers the whole bat, with a short lip that sticks up about an inch. Then I take a bag of clay (25lbs), cut it in half, and throw two cylinders about 3/4 inch thick. They are stacked onto the bottom slab, and the whole thing is pulled up and shaped.  This is all done at once, while everything is still wet. No drying of any pieces. I do not score when joining them, because it makes little air bubbles in the joint that are visible after pulling. Just make sure the joint is dry and they'll stick fine. I use a metal rib to scrape down the surfaces and get the slurry off. Pulling the walls gets everything joined securely. That forms the bottom 2/3 of the pot, up to the ridge that you see in the pot. I just leave the lip thick to create the ridge, which gives me a wide surface to attach the next ring. I let all of that stiffen up a little bit, then throw another half a bag into a ring, attach it to the top of the pot, pull and shape. I do score that joint since the two pieces are different moisture levels, and because I'm not pulling through the joint there's no air bubble problem.

[CactusPots]

On 6/28/2020 at 10:24 AM, oldlady said:

cactus,  how many big pots have you made?   is it enough so you have developed skill making them before getting to the point of firing any?    the photos show excessive thickness for any size pot.

try a few more that you cut through to see the wall and floor thickness before putting one in the kiln.

this reply was to the other thread and i don't know how to move it.

Throwing big pots is in fact a new thing.  The pots look good to me in the green stage, I don't see any reason not to bisque fire them.

We could probably have an interesting discussion on what is the proper thickness for "any" pot.  I'd maintain a planter should be thicker than a bowl.  The first one I fired was on its base and split in half when I threw it on the shard pile.  The wall thickness is about 1/2".  A better thrower (which I will be if I stick at this) would no doubt make a thinner pot, but I think it should work.

[CactusPots]

Here's another look at the pot's flaw. I just pulled on the crack and exposed this.    I'm going with the "don't fire big pots on their rims".  I have one left from this series, I'll try it right side up, on a waster slab, in the middle of the kiln.

 

[Hulk]

The colour gradient interests me. Might break some bisque (that I don't like much) later today; will report back. Would more firing time be indicated? Is there sufficient oxygen?

Is there lighter layer in the base portion as well? Looks like the base section is thinner; might more uniform thickness make a difference? There may be more than one cause o' cracks goin' on.

 

Broke some bisque - cone 5/6 buff and red clays - not seeing any colour gradients - uniform color across the section, electric fired, with powered vent, to cone 04. The thickest part is just over 5/16 inch, at the foot ring.

[liambesaw]

Wow it delaminated, that's interesting!  May be a temperature gradient involved from firing faster than the pot could equalize.

[Babs]

Are you possibly incorporating slurry from throwing into wall of pot as you throw?

Base trimmed and so thinner than walls.

Area from base to wall thicker can cause trouble.

Thicker pots, gradual longer drying required. Moisture trap

Not sure of your technique but looks like the joining may be trapping wetter area which is  causing the "inside wall" cracking evident up entire wall.

Horizontal crack...anywhere near your joining.

I've centred half clay required, dented top of that and added a further ball to that and centred again...just saying.

Opening clay..heel of hand, arm firmly braced,  moving slowly away from me to 12 o clock and thenback to normal opening works for me. 

Pres here opens with his elbow.

[glazenerd]

Have my concerns this clay body has formulation/contamination issues. The recent two samples are fired to? 

[CactusPots]

I appreciate all this feedback.  I had a few beginner courses 20+ years ago, but I'm largely self taught.  I mostly avoid areas that cause a lot of trouble.  Like this.

The delamination is entirely in the added ring section, so I'm thinking the primary issue must be in the way I opened the clay.  I must have pushed a layer onto the wall when pulling it up.  Not sure how I did that, but next time I try this technique, I'll have to be more mindful of that.

The clay body is Laguna Soldate 60 WC843    fired to 06 1823F

The color differential inside the bisque is a subject I never gave any thought to.  Sometimes a pot fired inside another will have this color change on the outside.  The kiln is a Skutt 1027 fired to 400 with the lid propped slightly, then closed.  Fired to completion with the top plug out.  Here's another example of this color.  I get it pretty regularly, but it doesn't seem to make a difference.

 

[Pres]

When in grad school, as a non declared student, I believed my throwing skills to be sufficient enough to start throwing larger. At the time Takaezu was all the rage, and I read a lot about throwing large, and sculptural ceramic. I started by throwing pieces that were multiple cylinders, and got to about  50" in that manner. Then I tried a coil piece, starting with a 24" base on a bat, with a 20# starter. Coiled up and thrown in steps for one week, 6' in the end, dried to about 5' in Summer 2 weeks later bisque fired then glazed and fired. Sold at student show after course was done for @$200 . Paid my studio fee. I could have never done it during a semester, or at home. The kilns were big enough, the wheels were enough I could monopolize one, and there was equipment to help me load it into the kiln, hand skid loader.  This class was about 1976.

One thing I did learn in all the reading was to not overlap the coil layers when pulling, pull each on the other, weld together at the join, but not to try to pull layer below into the coil above when pulling the coils.

Enough for me that I could do it. Now I usually only throw big with 3 sections if at that. Too much work. Still like to throw larger pieces, bowls, storage jars, lidded containers. Especially like combining slab and thrown pieces.

 

best,

Pres

[CactusPots]

Of course, big is a relative term.  For me, 25 lbs of wet clay is big and I doubt I'll go much bigger.  Most of my demand is for 8 lbs and less.

I joined the 2 sections at around 1 inch thick and then pulled up to my 1/2 inch final.  So maybe that's where the laminations came from.  I did the joining right after the initial throw for the bottom piece.  Both sections as soft as can be.  No slip.  ls that the ticket, or are you allowing some stiffening to get a thinner joint?  So in that case the joining is pretty close to the final form. 

[Pres]

If the bottom section is much drier than the top section, and you pull up the two together, you end up with lamination problems as the two sections of the wall are mismatched.

 

 

best,

Pres

[Babs]

I've seen potters torching outside f lower pot to stiffen enough to support the additional clay but well away from joining area.

[Pres]

Used to light a fire inside at PSU, allowed it. newspaper, or sawdust keep feeding for a while. Takaezu used to do it, where I got the idea. I think it was in my first Nelson.

 

best.

Pres