An experiment in Fritware Zero3

[Jeff Longtin]

Hey Min,

Interesting conversation. I only cast earthenware in the 80's when I just started out. Minnesota Clay mix. Having craze issues I soon moved to stoneware, Duncan. (rumored to have been "Bmix") and then to my own mix of cone 6 porcelain. (Dorothy Hafner)

Coincidentally my studio neighbor just bought a 100lbs of something called, "Zero4". I was just reading up on it before I saw this posting. 

Good Luck High Bridge. Great to see you taking this on.

 

[neilestrick]

11 hours ago, High Bridge Pottery said:

The Hymod clay needs about 25% more water than the Hyplas to get to the same consistency so do I mix to the same consistency or with the same weight of water? Seems fair to mix with the same amount of water but then one is a thick slip and one is the consistency of milk.

I would measure the drying time with the slip at or near the specific gravity that you're going to be working with, since you won't be using it in a milk-like state.

[Min]

Do you have the CEC/MBI numbers for the Hyplas, Hymod and kaolin you are using? Given that you will be deflocculating the casting slip I would go with the ball and kaolin you have access to with the lower exchange rates. 

[Babs]

C03 is used quite a bit in Oz. Basically to vitrify some of the clay bodies so functional pots can be made from the reds and white bodies usually fired a bit lower. D' Boos had a section of glazes  in her book made for that firing temp. range. The terra cotta clay went a bit browner but still ok, and vitrified. Just saying.

[Juxtaposie Jen]

5 hours ago, Babs said:

C03 is used quite a bit in Oz. Basically to vitrify some of the clay bodies so functional pots can be made from the reds and white bodies usually fired a bit lower. D' Boos had a section of glazes  in her book made for that firing temp. range. The terra cotta clay went a bit browner but still ok, and vitrified. Just saying.

If anyone has any info on that book - I’d love to see those recipes 

[High Bridge Pottery]

Can't see any CEC/MBI numbers on the data sheets. I can find a value for KT#1-4 on digital fire of 6.2 meq/100g

 

10 hours ago, Babs said:

C03 is used quite a bit in Oz. Basically to vitrify some of the clay bodies so functional pots can be made from the reds and white bodies usually fired a bit lower. D' Boos had a section of glazes  in her book made for that firing temp. range. The terra cotta clay went a bit browner but still ok, and vitrified. Just saying.

 

Babs what is C03?

[Babs]

2 hours ago, High Bridge Pottery said:

Can't see any CEC/MBI numbers on the data sheets. I can find a value for KT#1-4 on digital fire of 6.2 meq/100g

 

 

Babs what is C03?

Cone 03 firing. Thought you were aiming at that firing range? Neil E asked why Cone 03 . My comment really was an aside to say folk do fire to that cone. 

TheTony Hansen site indicates he does with the clay body he is playing with.

[High Bridge Pottery]

Ah got it yea I am aiming for cone 03. I thought you were talking about something I could add to the recipe like carbon trioxide.

[neilestrick]

I was just wondering why cone 03 when most low fire glazes are formulated for 06-04?

[High Bridge Pottery]

Would 1 extra cone make much difference to the glazes? I was planning to use more premade underglaze/stains and then make my own glaze that goes over.

There's no other reasons than that's where the article started and 1100c is a nice number to fire to I could lower it to cone 04 if I found glazes I wanted to use.

 

I am not quite sure how to put these next results in more than just a table. Do colours make it better

All I really learnt is there's not much point adding Calcium or Magnesium. Sometimes it seems to help a little but I am not sure adding 2-5% is worth it unless it imparts some better working properties.

Seems like I can use 50% Kentucky ball clay without too much of a problem with porosity, the Hyplas is not so good. Some of the tests went over the 20g limit of my accurate scales so the weights with 1 decimal place are not as accurate.

It does look like you can always add 5% Lithium Feldspar with good results and seems almost better than adding another 5% frit. I don't have a 10% frit with Nepheline Syenite to compare with but adding it mostly seems to make porosity worse.

 

[Min]

2 hours ago, neilestrick said:

I was just wondering why cone 03 when most low fire glazes are formulated for 06-04?

Hansen's Zero3 was the precursor to Zero4.  Link here to his recipe for that plus a couple glazes for it. When I was coming up with a ^6 casting porcelain I tried NewZealand Halloysite (what Hansen used for his Zero4), it's a funny material to work with. Needs a lot more mixing than grolleg or EPK, when I read up on the particle shape I found that it has a spherical or tubular shape rather than the plate like structure of grolleg and EPK. I probably didn't mix it enough, had little hard bits in the fired tests like Hansen speaks about in that link. Unless you need a super white I don't think halloysite is worth the cost and extra work needed to make a good slip.

Your charts and all the testing you are sharing are great Joel! Silica level looks better on the middle one in your post above, or maybe add some silica + lithia spar to the third one and see what happens?

 

[High Bridge Pottery]

Sorry I didn't realise I left the third recipe in Auto Unity so it's calculating to Al2O3 unity instead of flux unity which makes it look off. The all have around 69% mole silica.

It is amazing how different clays can be even with similar chemistry. I am pondering if you can get reduction at low fire so not too particular about it being white. I don't see why not but maybe I am missing something obvious.

Edited December 6, 2022 by High Bridge Pottery

[Babs]

2 hours ago, High Bridge Pottery said:

Sorry I didn't realise I left the third recipe in Auto Unity so it's calculating to Al2O3 unity instead of flux unity which makes it look off. The all have around 69% mole silica.

It is amazing how different clays can be even with similar chemistry. I am pondering if you can get reduction at low fire so not too particular about it being white. I don't see why not but maybe I am missing something obvious.

Not sure, relying on memory re reduction,  but some folk used to start reduction not far above 900dC and stop reducing quite low. Got lovely peachy and soft wines. Here, try to get stuff from John Eagle, he wrote about his practice, could be completely bad memory though. I had to fight not to get reduction.

[Kelly in AK]

Reduction is definitely possible, has an effect, at lower temperatures. In the albums on my profile page there’s one called “ Local Anchorage Clay” that has pots fired in reduction to cone 03. They’re vitreous, 1% absorption. The reds there are from copper, no stains. The black surfaces are from iron in the clay, no stains or oxides added. I reduction cool the kiln until around 1500° F, keeps the iron black. If not, it tends toward a dark brown where unglazed. I have found that if I reduce heavily through the firing that the clay gets less predictable. I’ll have sections of the kiln with slumping, bloating, and sometimes dunting. It’s a work in progress, I have a lot to learn. I imagine a clay with less iron would be less trouble in that regard. Presently I fire a neutral to light reduction until the end, drop 100° and hold for 30 minutes in oxidation, then reduction cool till 1500.°

[neilestrick]

8 minutes ago, Kelly in AK said:

 I reduction cool the kiln until around 1500° F, keeps the iron black. If not, it tends toward a dark brown where unglazed. I have found that if I reduce heavily through the firing that the clay gets less predictable. I’ll have sections of the kiln with slumping, bloating, and sometimes dunting. It’s a work in progress, I have a lot to learn. I imagine a clay with less iron would be less trouble in that regard. Presently I fire a neutral to light reduction until the end, drop 100° and hold for 30 minutes in oxidation, then reduction cool till 1500.°

It's also really easy to over-reduce when reduction cooling, and can mess things up. It really takes very little fuel if the kiln is sealed up halfway well.

[neilestrick]

8 hours ago, Min said:

Hansen's Zero3 was the precursor to Zero4.  Link here to his recipe for that plus a couple glazes for it.

I looked at that, and was wondering why 03 with him, too. Hansen's recipe is crazy expensive even if you use grolleg.

[Min]

46 minutes ago, neilestrick said:

I looked at that, and was wondering why 03 with him, too. Hansen's recipe is crazy expensive even if you use grolleg.

Yeah, for sure still too expensive for production level of work. I’ve been tempted to mix an earthenware with a brown midrange and aim for cone 1-2 but not sure if the work involved would outweigh the cost savings in electricity and kiln wear.  Hansen has an article on that too.  https://digitalfire.com/glossary/cone+1 

[neilestrick]

7 minutes ago, Min said:

Yeah, for sure still too expensive for production level of work. I’ve been tempted to mix an earthenware with a brown midrange and aim for cone 1-2 but not sure if the work involved would outweigh the cost savings in electricity and kiln wear.  Hansen has an article on that too.  https://digitalfire.com/glossary/cone+1 

That mix is a beautiful color, and if you have a pugmill then making the blend would be pretty easy, although still a time commitment. Also easy enough to have the manufacturer make it for you. The workability would probably be really nice, too.

Despite saying that Hansen's body is expensive, I really go back and forth a lot on my opinion on clay prices. On one hand it's a major layout of cash to buy 2000 pounds of a body that costs $2 per pound, but on the other hand, compared to the 88 cents per pound that I'm paying now for a good porcelain, the price could easily be made up by raising prices just a little bit. The cost per pot is still very low in the big picture, but having that much money tied up in inventory would be  horrible. You can make up a little bit of the cost in lower firing costs and longer element life, but nowhere near all of it. There's not going to be a financial benefit to $2 per pound clay. The red cone 1 blend would definitely come out ahead, though. Same price as what you're using now, lower firing costs. I imagine a cone 1 porcelain frit body could probably be made at a similar price to a cone 6 porcelain, since it wouldn't take as much frit at cone 1 and the neph sye would come into play more. I might have to take some of my porcelain and try some frit additions to see what happens.

[Babs]

Another fact from J eagle is he packs his fibre kiln with each shelf edged with bricks leaving only a small gap under next shelf, tantamount to each shelf being a sagger, just saying.

[High Bridge Pottery]

7 hours ago, Kelly in AK said:

Reduction is definitely possible, has an effect, at lower temperatures. In the albums on my profile page there’s one called “ Local Anchorage Clay” that has pots fired in reduction to cone 03. They’re vitreous, 1% absorption. The reds there are from copper, no stains. The black surfaces are from iron in the clay, no stains or oxides added. I reduction cool the kiln until around 1500° F, keeps the iron black. If not, it tends toward a dark brown where unglazed. I have found that if I reduce heavily through the firing that the clay gets less predictable. I’ll have sections of the kiln with slumping, bloating, and sometimes dunting. It’s a work in progress, I have a lot to learn. I imagine a clay with less iron would be less trouble in that regard. Presently I fire a neutral to light reduction until the end, drop 100° and hold for 30 minutes in oxidation, then reduction cool till 1500.°

Never heard of reduction cooling before, I will take a look at the photos. Yea I feel like if I just put it in light reduction from say 800c (1470f) then I should be able to bring out some iron spots. Nice to hear you can get copper reds too.

 

I wonder if there's a cheaper way to source high alkaline frit than from pottery suppliers. When you are getting into the 20-30% frit range it does start getting pretty expensive

I don't think I can get Ferro Frit 3249 here in the UK for the zero4 glaze. There is one low expansion frit that comes with zinc and a white frit that could maybe have low expansion? Just going to need lots of testing. There's probably a few recipes I could make larger batches of and start trying out glazing.

 

Been looking at the results again and it does seem that adding a small amount of Calcium can help reduce porosity, or I just messed up the tests

Edited December 7, 2022 by High Bridge Pottery

[Min]

10 hours ago, High Bridge Pottery said:

Calcium can help reduce porosity, or I just messed up the tests

Are these 20 gram tests? 

10 hours ago, High Bridge Pottery said:

I don't think I can get Ferro Frit 3249 here in the UK for the zero4 glaze. There is one low expansion frit that comes with zinc and a white frit that could maybe have low expansion?

Ferro 3249 is just under $500 / 50 lb bag here. (I've changed my glazes to remove it, too expensive now and I can make do without it)

Comparing the 3 frits, if you need a low COE one I'ld go with the 2279. If you are aiming for Hansens recipe increase the amount of 2279 to match the magnesium then tweak the silica etc. Might not need it at all. Would be interesting to see the melt difference between fritted magnesium vs supplying it from talc or dolomite, thinking it could be significant at low range.  COE figure on the 2270 probably doesn't represent real world tests given that zirconium will in theory increase COE but as it doesn't melt it acts as little road blocks in the glaze and decreases the chance of craze lines propagating. 

[High Bridge Pottery]

Yea they are all 20g tests. I am pretty sure the calcium is right as the pattern seem to match across all the tests. The only scale I have accurate to 0.001g has a max weight of 20g, the next one up does 0.1g to 3000g so I feel like the smaller batches are more accurate anyway.

 

I will hold off buying any of the low expansion frit until I try a few glazes and see if they craze. I have what I need for the zero3 recipe as a starting point.

[High Bridge Pottery]

Tried casting a few small shapes with B0118. Got to sg 1.7 using sodium silicate, still think I need to add a little more as it had slightly gelled when I tried to pour out after 15 min. Managed to get them out the mold after 1.5 hours so seems pretty quick at drying out. White spots are a few bits of plaster as first time using and I have been learning how to get a good surface finish from the plaster. Brushing on thin before the pour seems to do the trick.

[neilestrick]

On 12/7/2022 at 2:50 AM, High Bridge Pottery said:

Never heard of reduction cooling before, I will take a look at the photos.

When you reduce an iron bearing clay body, the iron goes from red to black, and then the surface reoxidizes during cooling. If you cool in reduction, then the iron stays black. You need a clay body with 4-4.5% iron if you want black. To do it well, you need to be able to seal off the kiln but still be able to introduce a small amount of reduction. In a wood burning kiln, that means sealing up all the air holes with clay, and tossing in just a couple small scraps of wood every 10-20 minutes as it cools, down to a temp where it won't reoxidize. Very slow and boring process. In a gas kiln you seal off the burner ports but leave a small pilot flame burning for the reduction. Introducing small amounts of air can result in bright flashes of color on the surface. The first photo below is a teapot by John Neely, who pioneered reduction cooling in the US at Utah State University. It's not black clay, it's reduction cooled brown clay. The second is a piece by Susan Harris of Southern Utah University. Susan is a master of getting bright flashing in her reduction cooling pieces.

  

[High Bridge Pottery]

Interesting stuff, sounds quite particular to get right especially at the end of a long firing.

 

Tried mixing up another slip with half of the Kentucky clay but it just turned into a solid mass when I tried to deflocculate it Think I must have added too much but I thought it would settle out not turn into a solid mass.