Partial glazing of large pot in soda fire

[Pyewackette]

The studio manager where I work has said that you cannot partially glaze a pot, say, by glazing the inside only, or the pot will implode- literally implode.  He says it will pull the clay inwards and cause it to actually break. If the glaze shrinks more/faster than the clay wouldn't it just crackle, and wouldn't that actually be a glaze defect?  If it shrinks slower, wouldn't it shiver off and then again be a glaze defect? 

I know compression between inner and outer glaze on the clay body is an actual thing but ... actual breakage doesn't seem reasonable to me with any glaze allegedly formulated to fit the clay body in question, which is supposedly what we have. 

I ask in relation to this pot:

It's around 3' tall (I will measure it next I'm in the studio) and was textured with slip added after trimming.  I plan to use flashing slip on the body.  I would like to use several different slips to get slightly different effects, he seems to think that's silly because he seems to thinks most flashing slips end up looking the same (I may have misunderstood his reasoning but he does seem to think its a waste of time and effort).

But I would like to glaze the neck and rim and inner rim with either Patrick's yellow or Autumn yellow, both of which turn sort of brown to tannish brown or very slightly orangey brown in cone 10 reduction.  Partly because soda firing just doesn't seem to work very well on the insides.  I plan to spray on both glaze and flashing slip(s).  I would spray the flashing slip(s) onto the bone dry work and then the glaze after bisque fire.

So if I glaze only the top inside and out is my piece likely to implode or otherwise do something bad because I didn't actually glaze the whole thing?

Edited November 2, 2023 by Pyewackette

[Chilly]

Personally, I think he's talking out of his .....sit-upon.

I do think not glazing both inside and out can cause glaze fit issues, but implode......

Test (in your own kiln) by making a small vessel, glaze as you want, put into a saggar and fire it.

 

Edited November 3, 2023 by Chilly
typo

[Min]

A well fitting liner glaze is usually always used inside soda, salt and wood firings for all functional pots. Wouldn't want to drink out of mug without a glaze inside it. If the liner glaze has a significant fit difference from what lands up on the outside of the pot then the pot can dunt / crack.

If you glaze the entire pot and then it's hit with the soda it can very well cause excessive running of the glaze due to the extra fluxing of the sodium. If you just glaze the top of the pot and leave a lot of room for it to run it should be fine. It depends on how much soda the pot is hit with.

Nope, flashing slips don't all look the same. I used a few on the vase below. The lighter orange one has titanium in it, the red doesn't. 

 

 

[Pyewackette]

@Min Well thank you, I feel much less weird now knowing that an accomplished potter such as yourself has actually gone the  multi-kinds of flashing slip route.  I think his issue is that he thinks the flashing slips we have will be indiscernible from one another after firing, but then why do we have 3 or 4 slips that end up all looking the same, I ask.  I'm good with subtle differences, and if they actually DO all come out the same, where's the loss.

I actually would like it to get runny and yeah, there's plenty of room for it to run.  Don't want to glaze the whole thing because I don't want to lose all the texture.  Nearly all my textured pieces ended up with glazes that hide the texture.  I always wet my pots and I literally dunk in and right back out, no 3 second holds here.  I wait for the first dip to be pretty dry and usually do a second dip if the first looks kinda thin.  Not having my textures disappear under the glaze has been an ongoing struggle.

[Hulk]

Do transparent and/or translucent glazes show texture better?
Highlighting textures with contrasting washes/underglazes/glazes - put on, then wipe off, leaving some behind in the lower and rougher spots - may help. 

[Pyewackette]

56 minutes ago, Hulk said:

Do transparent and/or translucent glazes show texture better?
Highlighting textures with contrasting washes/underglazes/glazes - put on, then wipe off, leaving some behind in the lower and rougher spots - may help. 

I've tried underglaze, then coated on top with a clear.  Totally hid the chatter marks.  Well maybe not TOTALLY, but it just looks weirdly uneven. I didn't wipe - Hsin Chuen Lin doesn't wipe, but then he's Hsin Chuen Lin and he's not stuck using whatever ancient underglaze you can find that you have to reconstitute from a hockey puck once you do find it.  Also he remembers to put the underglaze on first, THEN chatter.  *sigh*  Really I didn't wipe because the studio clay body is so ugly and I was hoping the underglaze wouldn't melt enough to fill in the low spots, but with the clear on top it did.

The celadons have typically shown the chatter marks, but the studio clay body is REALLY ugly when fired, sort of a greeny-yellowy-gray, like zombie skin.  Light zombie skin at cone 6 and dark zombie skin at cone 10R.  Looks awful under green or blue celadon, I'm trying amber celadon as we speak, but shortly that won't be an issue any more given I now have the option of not-studio clay.  Honestly I don't think the celadons look very good on anything that isn't pretty white, but I HAVE PORCELAIN now so that might help. I couldn't figure out why it looks ok on the test tiles, then I realized - they weren't on the studio stoneware.  They were on the studio B-mix. And not noted as such. That is at the city studio, not the one I usually go to.  We don't have any test tiles to speak of at the main studio because they threw them all out and are making new in the course of getting rid of/replacing some of the old glazes and clay bodies.  Thing is, they don't even buy the B-mix for students at the city studio, just the studio stoneware body.  So why all their test tiles are on B-mix is a question for the ages. 

I've read about borax or TSP washes on here and would like to try those, partly for purposes like this but partly just because its a tactile thing with me - when the clay body DOESN'T look like zombie skin, I like for it to be partially exposed or rather FEATURED as part of the design, but I don't like the rough texture.  For instance right now I have a sake jar that is finely textured on the top half, I would like to do as you say, put on some glaze and wipe it off, but then I DON'T want to coat it with the clear because it is very glossy (we don't have a matte clear) and also seems to make an underglaze melt, who knows what it would do to an already melty glaze.  At least that is what looks like happened the one time I tried it over underglaze.  It didn't help that that underglaze also turned out to be an eye-searing orange.  I mean I want some color on my pieces but I don't want to be burning out retinas. Most of the underglazes in the studio were purchased for hand builders with, shall we say, a different aesthetic.  They're pretty bright.  Although I had one go black on me - also not desirable, it was supposed to be a sort of tan.

So I was thinking maybe a pigmented wash using Mason stain or whatever would not either turn black or disappear (iron oxide disappears under many clear glazes, I don't know if that's a zinc thing or a CaO thing per digitalfire), wipe, overcoat with one of those borax or TSP type washes, and I might get both the hint of color in the grooves, keep the texture visible, "feature" the clay on the high points, and still have a nice smooth satiny texture when you pick it up. 

Of course I don't know how to make any of those washes LOL!

[Hulk]

Zombie skin, I have that!

:|

I've been filling the chatter marks since early on, which prevents little micro-crawls, where the glaze didn't wet all the way to the bottom of the mark, and, there's opportunity for highlight/contrast.

At first I'd used underglaze only; now I almost always use a glaze.

Depending on the materials, the marks can be accentuated, muted, and somewhat in-between...

I'm dampening the area with a sponge bit, then floating the material on the marked area - wet brush, pick up the glaze/underglaze, flow it on - the material goes right into the marks, less so on the surrounding area. Then wipe all with a sponge bit, leaving the marks filled and the surrounding area clean.
Allow to fully dry, glaze.

I'm still working on technique - get the marks filled in less time with less waste...

The little round sponges that come with tool kits, they are good for wiping away!
However, cutting purpose shaped bits from a larger sponge works, thanks Bill Van Gilder for the tip...

Edited November 3, 2023 by Hulk
schepellin'

[Callie Beller Diesel]

It sounds like at best, your tech is either grossly oversimplifying his explanations, or he hasn’t done a lot of soda firing. Or both. My wood fire and soda mentors all experimented with how different kaolins, feldspars and fuel types affected flashing slip recipes. The differences are indeed noticeable. Clay body also matters.

It is possible, under fairly specific circumstances, for a glaze that fits a clay body to pull apart a piece that’s only glazed on the inside. But the glaze has to be as thick or thicker than a relatively thin clay layer, and the piece in question is usually a wide flat piece with right angle walls. Often in this example the glaze will involve lithium as an ingredient. It does non-standard expansion things.

These are not your circumstances. These circumstances largely don’t occur in soda firing. I won’t say never, because we all know (or have been) That One Kid who did that thing once that still gets talked about.

If the walls of your pot are thicker than the glaze, which I would expect to be the case with a piece 3’ tall, you’re fine. 

If you want to highlight the texture of your piece, I think a light spray with flashing slip and carefully choosing the position in the kiln is a great idea. Sodium reacts with the clay body itself to form a glaze, which means that areas that are heavily exposed to the vapour can have sharp textures blurred. So you want to have the piece placed somewhere that won’t get fully blasted, but will take advantage of flame path depositing the vapour.

I suggest you’d want to avoid right in front of any soda ports if they’re spraying, or right in front of the bag wall if they’re dumping burritos or soda plaster lumps into the firebox. In either case, you also don’t want the piece to be right in front of the flue exit, but to one side of it could be interesting.

If there’s any salt in the mix, all bets are off and you’d need to ask someone very familiar with the specific kiln where the “wet” and “dry” spots are.

Soda by itself tends to be very sluggish in the kiln, which is why people either spray it, or mix it with water and something like whiting or sawdust that will help it disperse from the firebox more easily. So you can get some pretty pronounced flame records on soda fired pots. Salt will more or less explode when it hits a hot kiln, so it’s easier to get a more all-over coating, and it’s why it tends to take less salt to get an orange peel effect. A few soda artists of my acquaintance aren’t afraid to refire pieces that didn’t quite get the coverage they wanted on the first round. Most kiln bosses will prioritize items on their first ride through the kiln over re-fires though, so check with whoever’s firing the kilns what their preferences are.

 

[Kelly in AK]

It’s possible for glaze tension to crack a piece in half, but it’s unusual. For example a very thin piece, made of clay that’s over fired, glazed too thickly, glazed only on one side, and with a glaze that has very compressive fit is a good candidate.

That said, I do soda fire at cone 6, have done dozens of firings. My own work, my own kiln. Ninety percent of the work is glazed only on the inside and about 1” down the rim. A flashing slip is applied to wet and leather hard work (50/50 Helmer and neph sy). I’ve never had this problem in my soda firings. 

Michael Cardew discusses it in Pioneer Pottery, he treats it under the section on clay body defects and refers to it as “shattering.” It is a real thing, but generally happens under a particular combination of circumstances. I share his opinion that it’s best understood as a clay body defect. 

[Pyewackette]

@Kelly in AK Those are some really nice pieces!

At this point I think I'm just going to spray the whole inside and the rim/neck on the outside with a glaze and use the flashing slip over the rest.  That's assuming they get a compressor for the sprayer.  He says to spray the flashing slip at bone dry and its going to be awhile before that thing is bone dry LOL!

@Min He very well may be oversimplifying, and/or I am probably misunderstanding and misrepresenting.  I'm just trying to assimilate the flood of information!

Edited November 4, 2023 by Pyewackette

[Kelly in AK]

Sounds like a good plan. It’s a big beautiful piece! Worthy of a little more caution than normal. I’m hesitant to offer straight up advice, not knowing all the particulars, but I will suggest applying your flashing slip thin. Mostly because the piece will be dry and you want to avoid issues of fit/shrinkage, but also because a thin layer is sufficient and won’t hide the texture. 

[Min]

@Pyewackette, +1 for just using a very light spraying of flashing slip.

Also, I would pour the liner glaze not spray it. When you spray inside a form such as a deep bowl or vessel there is a huge amount of glaze blowback coming back out at you. I'ld spritz the inside of the (bisqued) pot with water at the bottom and lower part of the wall where the glaze will be thicker and do a quick pour of glaze of about 1/3 the volume of the pot then very quickly pick it up and swirl and dump the glaze out to coat the inside. If you are using the same glaze for part of the top / outside then quickly dip that area after doing the liner.

I'ld also hold this pot back from your first soda firing. I would suggest taking some less precious pots, take some really good notes on what slips are on each pot, application details, where they are in the kiln etc. Learn as much as you can from the first firing, how other peoples pots turned out and any details you can get about those pots and the firing then apply that knowledge to the slips/glazes/placement/firing of this large one.

[Pyewackette]

@Min Wow I'm having a hard time figuring out how to pour glaze out of that huge pot.  It's about 3' tall (I'll actually measure it when I go to the studio later today, they don't open until 1). I'm pretty sure I'll need help.  I'll have to enlist the Studio Manager's help, most likely, I hope he doesn't feel insulted when I don't take his advice re imploding pots.  I'm guessing he was being hyperbolic so maybe it'll be ok.

But as for it being precious - it's really really not.  If someone hadn't asked for it from me for charity it would already be squashed.  It looks WAY BETTER than I think I had any right to expect for a first effort and using that clay but it is NOT not not up to my standards for work to be kept.  It is more or less ok when you're looking at it but that thing is NOT centered rim to foot.  The rim ended up way off center, so far off center I couldn't do a thing to improve that rim because spinning it was a lost cause (and me plus handbuilding, also a lost cause).  He had us throw the bottoms and then coil up using handbuilt coils and I obviously failed in a big way to keep the thing centered as I went up.  I think I'll try a "big pot" again (but not that big because the Big Things Class is over and I don't want to tick anybody off being a kiln hog) only this time (or however many throw/squash cycles it takes) I'll do it this guy's way:

 

That thing is over 3  hours long but if you go to 34:00 ish you'll see where he is torching the thrown base, taking some measurements, and then adding a big fat EXTRUDED coil AND THEN sort of "throwing it in".  I think I can do that!  And end up with something much less off center and better looking.

The pot as she exists has many many flaws, even if you ignore it not being centered rim over foot.  For one thing when I threw the base I envisioned a much much smaller big pot of the moon jar variety.  He egged me on repeatedly to make it bigger so the foot ended up much much smaller than I think it ought to be for a pot that tall, and there is some oddness that I covered up with trimming and slip where I had started to bring the shoulders in at what ended up being about a third of its final height.  Pretty sure the walls are of widely varying thickness as well.

I mean really.  Not precious.  I think I'll just ask his permission to make another big but not quite so big pot and squash that one anyway.  The charity thing isn't until April so there's plenty of time, I have no use for Big Things myself so I can just make another to give away.  Plus throwing it in my own clay has got to be easier now that we have Real Clay available.

What do you think of a manganese speckled clay like Peppered Creole in soda firing?  I don't have that clay yet but I hope to have it very soon, maybe as soon as this afternoon if the shipment arrived as expected.

Edited November 4, 2023 by Pyewackette

[Hulk]

Probably need two or three sets of hands to liner glaze that pot!

Maybe
  a) a piece of scrap carpet (or somewhat) on the floor to pad the base
  b) something to lean the pot on so it sits at 45° or so, and can then be tipped up and rolled along the length of, also padded with carpet or somewhat
  c) a long pan to catch the poured-out glaze

Pour glaze in, lean the pot over on the thing, lift the base* to the point where the glaze is about to pour out, roll the pot along the something whilst pouring out!
Voila?
 

*Risk, of course, that the pot breaks on the pivot point, hence, larger and softer could be better.

[Min]

22 hours ago, Pyewackette said:

What do you think of a manganese speckled clay like Peppered Creole in soda firing?  I don't have that clay yet but I hope to have it very soon, maybe as soon as this afternoon if the shipment arrived as expected.

Nope. Bodies containing manganese shouldn't be fired over ^5 maybe a cool ^6. If you want that speckled look then find a ^10 body with iron particles for the ^10 soda firing.

[Kelly in AK]

While it’s not quite the same as what you have to deal with, it is fun to watch these old potters glaze big pots. And they glazed them green, which is wild to think about too. 

Isaac Button glazing some big crocks (around 4:30):

 Burlon Craig glazing a crock and a bottle (around 2:00):

 

[Biglou13]

On 11/2/2023 at 11:24 AM, Pyewackette said:

But I would like to glaze the neck and rim and inner rim ……

So if I glaze only the top inside and out is my piece likely to implode or otherwise do something bad because I didn't actually glaze the whole thing?

My vote is that it will not implode

[Pyewackette]

On 11/5/2023 at 9:52 AM, Min said:

Nope. Bodies containing manganese shouldn't be fired over ^5 maybe a cool ^6. If you want that speckled look then find a ^10 body with iron particles for the ^10 soda firing.

I actually just realized - well I realized Sunday morning, I've been playing catch-up with housework today due to spending all the open studio hours at the studio (closed on Mondays) - that ALL the clay bodies I ordered are cone 6, including both the speckled clays.  So I should have known.  They do say those are good for cone 4 to 6 so I should be ok at cone 6 with those.

As of Sunday the Alligator order was  not yet in, hoping it will be there when I go in tomorrow afternoon.  There should be a couple of cone 10 white stonewares on the studio order, and then the clays I ordered.  Looking forward to both.

I'm throwing a lot better and a lot faster these days.  Still a long ways to go but I can see light at the end of the tunnel, and its not a train for a change LOL!

At any rate when I get some cone 10 stoneware I'll see about going big again.  That's been a goal, but it seemed out of reach until just the last couple of weeks.

@Kelly in AK It's so weird, I was just reading about Isaac Button somewhere or other - or had been just before I read your posting.  I've already forgotten what the exact context was but it was in regard to throwing big. 

[Callie Beller Diesel]

Issac Button is an absolute beast! Love it.

I’d be inclined to use a modification of Mr. Button’s glaze method on the inside. Instead of swirling the glaze with a cup, get a soft squeeze bottle, like the kind you’d fill with ketchup or mustard, and put the pot on a banding wheel or slowly turning wheel. Squirt the glaze flow at the widest part of the inside of the shoulder as the wheel is turning, and let it flow down, and pour out any excess. When you dip the outside top quarter, roll the pot slightly to make sure the glaze gets the inside bit that’s still bare. 

[Pyewackette]

Well I finally got around to measuring this today and I was WAY off.  It was 21" tall.  To be fair, that is more than 1/3rd of my height!  At any rate I smooshed it and discovered a couple of things, firstly the coiled sections were much more even than I would have thought but very thick at 1/2".  And the bottom thrown part was also very even, but only a scosh more than 1/4".  Also as I pulled it apart it came apart along the coils.  Not sure if that means anything.

The Armadillo order has yet to arrive but when it does get here I plan to score some light stoneware and try again.  I COULD use the studio clay but ... all the new clays (not counting the Raku) so far have been so much easier and more pleasant to work with.  Looking forward to doing it again only better LOL!