waster?

[CactusPots]

It was suggested here that I use a waster slab underneath to support the bottom of pots like these.  The space between the feet is almost 12" and 1 1/2 " deep.  A solid piece of clay like that might be 10 lbs or more and particularly difficult to dry thoroughly.   Maybe something like a trivet?  Quarter inch slab with lots of little feet?  Or maybe just lots of inch and a half blocks?

I don't think I've ever heard of a waster slab before.

[liambesaw]

Doesn't have to support the entire bottom.  Roll a thin slab and put a couple of supports if you want them.  The slab will shrink with the pot so the feet dont snag/drag.

[Min]

Much smaller scale but for my butter dish lids which I fire separately from the bases I slab roll scrap clay about 2-3mm thick and cut donut shaped waster slabs. Dried between batts or boards, used once and tossed. Sometimes I bisque them but since clay doesn't shrink much between dry greenware and bisqued it's not necessary to do this. If your clay plucks  put some kiln wash on them.

 

[neilestrick]

Waster slabs can be super thin. I make mine 1/16" thick. They do not have to be totally flat, it's okay if they crack when you set the pots on them. They'll still work. No bisque needed. Use alumina wax to keep the pot from sticking.

[Sorcery]

2 hours ago, CactusPots said:

I don't think I've ever heard of a waster slab before.

Right? Always cookies, same thing right? The name "waster slab" gives it this whole new purpose.

I recently used one for the first time to catch a jumping glaze. 130 Porcelain.

And rim fired a couple 547 stoneware pots  that took on some "character". 

I learned in the wood fire that stacking different clays on wads was enough difference to crack them, so I make sure to use the same clay for these things. Less they stick, shrink different, and tear each other apart.

The thinnest 1/8th slab slats work.

It is important to me, that it be one continuous piece, otherwise each chip is shrinking independently, limiting the assistance it is providing, possibly becoming a detriment.

Ribbed equally in all 4 directions on both sides at least twice, flipping between boards.

I've noted almost every molded and repeated foot design is built with this drag in mind, small contact points, rounded heels, and extra coils placed on the inside connection helps minimize drag and faults should they stick.

I think in the future I will religiously use alumina wax between. 

Sorce

[neilestrick]

20 minutes ago, Sorcery said:

Right? Always cookies, same thing right? The name "waster slab" gives it this whole new purpose.

I've always considered cookies to be re-usable slabs that are intended for catching glaze that runs too much. Cookies that have already been fired won't function the same as a waster, as the slab needs to shrink with the pot.

[CactusPots]

For the pots I pictured, I'm mostly worried about the bottom cracking.  Am I supporting the feet or the bottom with the waster slab?  My thinking was a slab across the bottom either taking the feet up or  very nearly.  Not right?

I'm mostly interested in not having problems with the bisque fire.  If the goal is just to prevent the feet from sticking, a layer of grog should do the trick.  I've been told that there isn't much shrinkage in bisque, would the waster slab be intended for glaze fire?

Most of my pots (probably not these) get cookies of sliced soft brick under each foot.  Mostly because of running glazes rather than cracking. If it comes out of the bisque perfect, it will usually come out of the glaze perfect.

 

[neilestrick]

32 minutes ago, CactusPots said:

Am I supporting the feet or the bottom with the waster slab?

The feet. The waster will prevent the feet from sticking to/grabbing the shelf. More necessary in the glaze fire, but wouldn't hurt in the bisque. You can use the slab for both firings.

[Mark C.]

Its the feet as the slab and fgeet shring at same rate in a bisque and the glaze fire.Thoise small feet will drag and tear/crack on a slab the whole thing moves and the waster slab takes the tearing and sliding. roll or throw them thin . Not much clay at 1/8th inch or more.

Its an easy thought pots shrinks and drags on a shelve-siting on a clay slab same thing but  now pot is on a magic carpet /slab and the carpet takes the slide /abuse

[Sorcery]

1 hour ago, Mark C. said:

 pot is on a magic carpet 

Nice! That's an excellent way to put it!

Yeah I would definitely use the same slab for both firings, this way it's even, and most the same.

@CactusPots I've never had a bottom crack, foot separation is most likely. 

I think some clays can warp if a foot catches, that can be the worst case scenario, because it can deform it in such a way that of the next shelf is close it can stick at the top. I believe it is more prominent in hand built wares, since throwing aligns the clay particles for rigidity.

Will this be the largest span you've done?

I'm firing my longest to date soon. Looking for all the info I can muster!

Sorce

[CactusPots]

Will this be the largest span you've done?

Since my shelves are 19" square, these pots will just about fill it up.  I can't remember anything bigger.

Every crack tells a story.  Mostly, I think mine are forming and drying issues and not so much feet sticking to shelves.  Also, I think the bonded silicon carbide and the advancers don't tend to stick to stoneware.  What I was asking about is mostly concerning the 12" expanse of the bottom

Isn't the largest shrinkage from wet to bone dry or maybe leather hard?  I should do some measurement tiles to see when the largest shrinkage occurs.  I'm aware that not allowing movement in an early stage could set up a crack in a firing.  You'd blame the bisque, but the problem might have been caused earlier.

[liambesaw]

1 hour ago, CactusPots said:

Will this be the largest span you've done?

Since my shelves are 19" square, these pots will just about fill it up.  I can't remember anything bigger.

Every crack tells a story.  Mostly, I think mine are forming and drying issues and not so much feet sticking to shelves.  Also, I think the bonded silicon carbide and the advancers don't tend to stick to stoneware.  What I was asking about is mostly concerning the 12" expanse of the bottom

Isn't the largest shrinkage from wet to bone dry or maybe leather hard?  I should do some measurement tiles to see when the largest shrinkage occurs.  I'm aware that not allowing movement in an early stage could set up a crack in a firing.  You'd blame the bisque, but the problem might have been caused earlier.

My clay shrinks about 5% in the glaze firing and 8% between throwing and bisque.  It's not as much but in the glaze firing the clay is pyroplastic so it is much more likely to warp, tear, pull, etc.

[Mark C.]

Stoneware is so forgiving-working with porcelain you get burned more.

[Sorcery]

16 hours ago, CactusPots said:

drying issues and not so much feet sticking to shelves

I dry on paper over glass to keep em level and allow for slide them too. That is very key.

Are you getting what I call, " S cracks that aren't S cracks because there are holes in the bottom?

Any pics we can read the story of?

Is that all Amador? Do the bottoms sag on you?(that's for me, my bottoms sag a little.)

What's your drying process? When are the feet added?

Sorce

[CactusPots]

I've never made pots like these before.  I'm not the guy who makes the same stuff over and over.  My primary goal is to keep myself entertained, not pay the mortgage, so there's always a level of uncertainty.  I don't like failure any more than anyone, but I do like to keep challenging myself.   So I'm just trying to learn from advice as opposed to trial and error.  Not sure where the "waster" concept fits for me.

My drying process is initial slow drying in garbage bags, on paper initially, then on non stick bats.  Plexiglas or masonite.    Turned inside out daily.  Then dried under towels.  Finish in the (right now really hot) sun.  One of the 2 in the pictures is thrown and the other is handbuilt.  The thrown is going to have fatter "cheeks" otherwise fairly uniform.  All construction, whether added feet for thrown (Soldate 60) or the totality of the hand built (recycle about 20lbs)   is done as wet clay as possible.  The handbuilt is done on a hump mold in one session.  Body---feet---rim.

I did really poorly with the last "large" pots.  2 piece thrown.  So these are different methods.  We'll see.

[Sorcery]

Any notes on why the others went poorly?

Forgive my pestering, I AM trying to pay the mortgage, but I want you to be successful just the same! I get not making the same stuff all the time, therefore also understand how much it sucks to have them come out wanked.

Hopefully this conversation replaces the need to do things repetitively to get them right!

Note, my humidity is likely higher than yours, indoors between 40-80%, so there's that ...

But I have been leaving out everything, completely ignoring all the drying rules (except my own) and nothing cracks (during drying) anymore. Ever try it?

I keep listening to folks talk about the hundred things they do to prevent s cracks that don't really help, so I have to ask where you stand on the understanding of them.

I look at the bottom (or any enclosed panel) of a pot like a dream catcher. If the edge gets dry and set to size while the middle still needs to shrink, s crack, because the middle can't pull the sides in, so it tears itself apart in the middle, or when holes are present in the bottom, wherever it is weakest. This usually isn't at the holes because the act of making the holes makes them stronger. (Porthole Theory)

This is "s cracks that can't be a cracks" , bit they still are.

Anyway. For that reason, I would cover the walls of your pot and dry the bottom while upside down for x, then simply turn it over and leave it out after. This way some of the moisture will fall down onto the walls to keep them just wetter than the bottom, after that the danger of a cracking passes.

Then walls, especially tapered as such, should be allowed to dry right side up, since they dry top to bottom, then it shrinks into the smaller ring.

Whereas upside down, the smaller ring is drying first, therefore getting smaller than the ring below it. Which puts it at odds with itself.

I figured you may be able to negate the bottom being too wet initially, by rolling the circle slab, allowing it some dry time, then forming your walls with an added sausage. That way you can skip the part where you have to dry the bottom more, cuz it could be dryer already. And they could just be left out in the hot sun.

I can't talk about how I want to buy one, but I hope they come out well!

Sorce