Mad Science in the Mud: Or, Franken-earthenware

[Pyewackette]

So @Min sent me down a clay-lined rabbit hole with this post:

Thanks a lot!  NO REALLY!  I loves me a good rabbit hole.

Turns out that stuff is FREAKIN' EXPENSIVE (but still interesting).  The guy who is working on it says they would have to sell the porcelain version for "$150 a box". As far as I can tell, a box is 25 lbs (unless its something else close-ish to that in kg, he's Canadian).  And the $150 is Canadian Money or about $118 in American Dollars.  Still a LOT. The red earthenware version uses 1/4th the amount of frit so I assume its not nearly as expensive but probably still not exactly affordable.

But it turns out, unbeknownst to me who has always been told "earthenware MELTS at higher than cone 04" - you can "overfire" MANY earthenware clay bodies to improve the absorption and increase strength/density.  They will not (necessarily) melt all over your shelves.  Or even bloat. Some even reach stoneware strength with near zero absorption by cone 2, sometimes even less.

https://insight-live.com/insight/share.php?z=No2m98AEhJ

On that page he gives a recipe for a terracotta clay body that he says reaches stoneware strength at cone 02.  He formulates this as a casting slip but says 

Quote

To make a plastic version we are adding 3% bentonite.

I assume by "plastic version" he means something throwable?  He says it fires to porcelain strength by cone 4. 

I love earthenware but have always been told it is impractical for utilitarian ware.  Since this clay body is not available for purchase through his company (Plainsman Clay in Canada) I assume there is something impractical about it, like difficulty finding or formulating glazes that fit the body maybe.  For many of the things I want to make glazing is not necessary.  In fact, if a glaze crazes it might even be preferable as a decorative feature.

I'm going to try to get the recipe for the clay booty I recently scooped up from the studio so I can try to figure some things out.  Where do you learn this stuff???  WHY DOESN'T EVERYBODY WANT TO KNOW THIS STUFF???

I haven't had this much fun in decades ...

[PeterH]

Historical  aside Code stone. Sold as an artificial stone, it was really a ceramic with a very narrow firing range.

Coade stone https://en.wikipedia.org/wiki/Coade_stone

The Secret of Coade Stone https://tinyurl.com/y2ckdhyy

What is Coade stone? https://tinyurl.com/2s3b5j76

[Min]

41 minutes ago, Pyewackette said:

Turns out that stuff is FREAKIN' EXPENSIVE (but still interesting).  The guy who is working on it says they would have to sell the porcelain version for "$150 a box". As far as I can tell, a box is 25 lbs (unless its something else close-ish to that in kg, he's Canadian).  And the $150 is Canadian Money or about $118 in American Dollars.  Still a LOT. The red earthenware version uses 1/4th the amount of frit so I assume its not nearly as expensive but probably still not exactly affordable.

Part of the reason Hansen works the price out at $150- CA a box is the porcelain he gets that figure for uses Halloysite (expensive), 30% frit (expensive), VeeGumT (expensive). If what he says holds true for an earthenware version of that clay needing only 5% frit then adding that amount of Ferro 3110 would add about $10-20 to 100 lbs of your dried free scrap earthenware (if it works). If the earthenware needs more plasticity (throws better) then 1-3 % bentonite (inexpensive) could be added, no need to use VeeGumT in earthenware. If my studio wasn't packed up I would mail you a bit of 3110 to try this out. Would the studio you go to sell you a little if they have it?

Some earthenware can be fired high enough to produce a fairly tight body without bloating, it's the old test it and see what happens. (using a drip saucer under test pieces).

BTW Boxes of Plainsman clay are 44 lbs.  Hansen doesn't own Plainsman Clay.

[Pyewackette]

@Min 44 lbs, ok, I just couldn't find anywhere on the site where it said how much was actually in a box LOL!  So that would make the Zero3 or Zero4 (whichever version he's favoring now) porcelain about $2.70 USD per lb retail.  It might be a little bit cheaper if you make it yourself but probably not by a lot since you wouldn't be buying in industrial quantities. I hadn't thought of the additional expense engendered by all that other stuff in the porcelain.

I could quite easily see the additional expense of the frit added to red earthenware to make that red earthstoneware (see what I did there? Wordsmith, me!) - in particular, unlike most red earthenware bodies that I know of, that body doesn't lose its red coloring as firing temp increases.  Lots of red earthenwares that I've seen are lovely after bisque and just sort of brown after firing to maturity.

Plainsman seems to be reformulating their clays to eliminate talc (gee, I wonder why!) and it seems like as they do that, the reformulated clay bodies mature earlier and improve in overall density.  Is it safe to take it as a sort of rule of thumb that talc in a clay body lowers its potential max firing temp, effectively weakening the final fired product?

I don't know if they have that frit at the studio, but given supply issues atm, they may or may not sell me some.  I'm pretty sure in normal times it wouldn't be an issue but these are not normal times ...  I'll ask though.

But first I have to whip my clay booty into throwable shape and do some test firings.  I may not be able to actually fire them until my little kiln gets here - I mean at other than the studio-normal bisque of cone 06.  While they haven't eliminated the white earthenware, nobody is currently working with it either (and I actually don't know what cone they use to fire it to maturity). Of late firings have been quite delayed.  I had pieces on the glaze shelves that didn't get fired for months (so did others) and bisque firings are lagging as well.  Not sure what's going on but I'm guessing there was some, shall we say, CROWDING of the schedule going on due to two recent studio-related events that involved ceramics sales.  I'm guessing some people's production runs were prioritized over classes and the rest of us.  Just as a guess.  Possibly if that run on kiln space is over now I can get some space in the smaller kiln (which is not tiny, about 2 to 3 cft I think).  That'll make test firing easier.

For protecting the kiln shelves, would bisqued stoneware trays be sufficient? Or should they be fired to maturity, given bisque at this studio is cone 06 and I'll be going above that while testing?  To make sure the trays have shrunk all their gonna shrink and don't develop cracks or other flaws when fired at higher than bisque temperatures.

Edited April 25, 2022 by Pyewackette

[Callie Beller Diesel]

Shelf protectors like that are sometimes called wasters because they’re not expected to survive.  If you’re making them out of a stoneware you know to be more refractory than the earthenware you’re testing, shrinkage isn’t going to be a big issue. But consult with the head tech person at your studio to see how they want you to work that. It’s their equipment, and they may have preferences. 

If you liked Tony’s articles on glaze and clay experiments, you’re gonna love the materials listings he’s got. Here’s the link for talc, and the why’s and wherefore’s of its use in ceramics. https://digitalfire.com/material/talc . It’s usually added to low and mid fire clay bodies to help with thermal expansion/glaze fit, but there’s other stuff too.

Digitalfire is a godsend to us all, as is the Glazy calculator. You’d also like the Potter’s Dictionary by Hamer and Hamer. Although that book is a bit of a spend, it’s worth every penny.

[PeterH]

1 hour ago, Callie Beller Diesel said:

You’d also like the Potter’s Dictionary by Hamer and Hamer. Although that book is a bit of a spend, it’s worth every penny.

As an example here is the entry on cracks http://ceramicsfieldguide.org/pdf/materials-handouts/ClayCracks.pdf

[Kelly in AK]

I use local Anchorage clay, it’s considered a mediocre red earthenware here, no one really uses it. You’ve got to be discriminating when collecting to get the good plastic stuff and I add 1.5% veegum to help it play nice.

Interestingly, at 04 it’s a bright orange, porous, but strong earthenware..  at 03 it is darker, completely vitreous (<1% absorption), and really strong. Like, I drop it on the floor and it bounces kind of strong. At cone 3-1/2 it’s a bloating slumpy mess. 

This is as opposed to the clay I got from Sheep Mountain a couple hours away. Threw like a dream right out of the bucket. Firing was a different story. Went from earthenware to ceramic foam in one cone. And I mean foam, frothy bubbling foam. 

Love the Rabbit holes. 

[oldlady]

i cannot find the zip code for nowhere so i cannot send you some of the 3110 that is filling a plastic shoebox on my shelf.   maybe i should look for rabbit hole but there is not even a state name.