High Bridge Pottery
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Posts posted by High Bridge Pottery
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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.
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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.
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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
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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.
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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.
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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.
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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?
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I only tried 50% kaolin in my first tests 41-44 with 20% frit. I didn't notice that much difference in drying times but I need to do some proper timed tests. The porosity did increase a bit.
I haven't quite figured out the best way to test drying times as all the clays react differently to the same amount of water. 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.
Yes there should be a reasonable saving in wear and tear on elements and kiln. I didn't know how to really calculate the savings per firing so left it out of my cost theory but it is an added bonus.
I only started with cone 03 after copying the idea from Tony Hansen of Digital Fire https://digitalfire.com/glossary/zero3
It could be a good idea if I want a white body to fire a bit hotter. The kiln can manage 150c/h (270f/h) to 1100c (2014f) but then it slows down a lot. After 1200c (2194f) it climbs slower than 60c/h (108f/h) and maxes out around 1260c (2300f)I hope I can find some glazes that work, there's a few suggestions in the digital fire article so I do have somewhere to start. Should get onto mixing glazes soon. Need to source some colours/stains/underglaze too, looking forward to trying out some lowfire ones.
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Thank you
a bit of method and a bit of madness I enjoy sharing what I am learning and always learn a lot from people on here. Nobody in real life wants to listen to me talk ceramics 
I think the small particles size in the Hymod is good for low porosity but bad for low drying times.
There is test 72 that has 65 Hymod, 5 Frit and 30 Nepheline Syenite that has 2.78% absorption so I would think having 10% frit instead should be around 1-1.5% absorption. I will run a test and see if the theory works.
It's interesting that 76 with 32.5 hymod 32.5 kentucky 5 frit and 30 Nepheline Syenite has 2.09% absorption. I wonder what is happening there, a little more silica and less alumina in 76 but not that different.
I was hoping the Nepheline Syenite would do a bit more melting. I have a few more tests drying adding Petalite and Dolomite with 20-30% Nepheline Syenite and 5% frit so hopefully one of those will be lower than 1.5%
I did think ball clay comes with extra silica so I might not have to add any. There's no real way of telling what CTE the clay will be. It's funny that you add silica to clay to increase expansion but add it to glazes to decrease expansion.
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Just been concentrating on lowering the porosity of the clay so haven't wanted to add any silica yet.
No idea if the glaze may shiver or craze so just leaving that until I have a clay body I am happy with. I may end up needing to add some silica but might be easier to just change the glaze if I find a body that casts well and low porosity.
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Next set of results is a mixed bag, tried adding some Nepheline Syenite and found another ball clay to try that is meant to be better for casting/drying. The Nepheline Syenite seemed to do a lot for drying time. Even at 10% the tests were pretty much dry in 40 hours instead of 80! It also makes the porosity a lot worse
but seems to get lowest around the 30% mark.
B0076 looks like it could be promising if I add some Lithium and mess with Ca/Mg a bit to get under 1.5% porosity and have better drying properties. Need to find the right balance for the good and bad of each.
The more I look at the chemistry the less I am using unity, I find it easier comparing the % analysis.
Seems there is a new button on digital fire for R2O3 unity but that still doesn't seem as useful as % analysis.
It is amazing just how much frit can change the melting characteristics. These two recipes with similarish chemistry but 3% difference in absorption.
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Depending on the frit it is around the same price to a bit cheaper to buy spodumene. Petalite is maybe half the price.
Actually you can buy 25kg of 3110 for £155 and 25kg spodumene for £286. A few places seem to be saying it is no longer available. Another site has 25kg spod for £188
The wollastonite seems to be doing strange things or I went wrong somewhere but I am pretty sure I got everything right. 10% seems to be the sweet spot. I am planning to cast but I will keep that in mind if I do try throwing.
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The UK has a lot of problems and seems to keep making them worse. Those prices are with a so called 'price cap' and then additional government help, its worse for business with some having a 400-500% increase. Feels like this is just the beginning
anyway I shouldn't get started.
Yes that's right, I should add some units to the axis. I have been doing (Wet Weight - Dry Weight) / Dry Weight * 100 to get absorption values. I didn't look at the price of Spodumene until weighing the fired samples today and it's not much cheaper than the frit.
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Have some interesting results from my Calcium, Magnesium and Lithium experiments. Might have to swap the Spodumene for Petalite as it is cheaper but I had both lying around and went for Spodumene.
These tests took about 80 hours to dry
Starting mix is 20g dry ingredients and 13-15g water. Need to run more tests adding other clays and feldspars to reduce drying time.
There seems to be a Calcium and Magnesium sweet spot where too little or too much makes it more porous. The Lithium just seems to reduce porosity.
All tests with 5% frit but I have tried to annotate the graphs and reorganise tests as my numberings went a bit all over the place as I came up with ideas. I ran a pure ball clay sample and added the 5% and 10% frit data from last time to the left of the chart for comparison.
These didn't actually make it to cone 03 and much more like cone 04. Cone 03 made it to about the 2-3 o'clock position so need an extra 10 min hold on the next firing.
Another graph of some 5% Spodumene 5% Frit + extras
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You can get reasonable results using laser printer, underglaze/oxide mixed with linseed oil and a gum arabic solution.
- Ben xyz, Babs and Callie Beller Diesel
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I felt like the OP was more of the opinion that even if you provide a warning is there really any need to share them so I felt it was a bit mean to blame the glazy user when everybody does it.
It's good to provide the warning but that doesn't always transfer with the recipe. I think it should be down to the end user to understand what they are dealing with but a lot of people may see a glaze they like and breath through their nose as an extra precaution.
- Kelly in AK and Babs
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I am hoping to get closer to 10% frit with the right mix of clays and flux but the early tests are promising
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I am not exactly sure this is the recipe they are trying to create but when places like here publish a recipe with 45% Manganese as "some of our favorite cone 6 glaze recipes in a convenient recipe-card format, perfect for printing and taking to the pottery studio" you can't really blame them.
https://ceramicartsnetwork.org/freebies/guide/15-tried-and-true-cone-6-glaze-recipes
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OK I will shoot for anything under 1.5% as a good starting place.
Tests 41-44 are a mix of 40 hyplas ball clay, 40 kaolin and 20 frit and that takes me from 0.2% to 1.55% but I do need to try with the hymod ball clay. I am hoping my experiments with calcium will bring the porosity down a bit so I can add more kaolin without needing 20% frit. Feldspars could also work.
No bisque tests yet, but I am thinking 800-850c maybe cone 014-012.
There's a lot more clay options from imerys who seem to supply it but you have to be a company even to talk to them. I might be able to convince a supplier to buy in new ball clays and kaolins.
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There don't seem to be many options here when it comes to buying powdered red clay. Quite a few white earthenware clays but from what I can tell they are a 50/50 mix ball clay to talc anyway. I have never been the biggest fan of red clay but if I can find some I will try it out.
The hymod clay and 5% alkaline frit (B0006) is already down at 1.2% porosity. It all depends where I want to put a line in the sand and call good on the vitrification side of things, anywhere under 3% seems OK.
I am hoping to add some feldspars soon but none in my old stock. Running tests with 5% frit and 5-10% whiting, dolomite, talc, wollastonite and spodumene to see how that changes things. Need to add something to speed up drying and keep it melting.
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I have always wanted to experiment with fritware and only having access to a small kiln that struggles to reach top temperatures I thought it may be worth trying out.
First some vague calculations to see if it makes sense.
I think electricity prices in the UK are pretty extortionate right now at £0.30-£0.60p a kwh. My kiln takes at least an extra 2.5h to get from 1100c to 1260c+ and at 3kwh * 0.40p * 2.5h = £3 extra a firing if I am getting a "good price" on electricity
Clay can cost anywhere from £0.40 per kg to £1.30 per kg and I am assuming around 25% of that is water. A powdered stoneware costs about £1.50 a kg so lets call it £1 a kg for a ballpark figure buying 100-250kg a go.
I could fit maybe 10 mugs in my kiln at say 450g a mug so total clay cost would be £4.50, with the extra £3 a firing that means I can 'break even' with a fritware body costing £1.66 a kg. A Larger kiln should work out more efficient on energy I think so less extra cost.
I have two ball clays and a kaolin kicking around so after reading kaolin can take up to 30% frit I decided to start with the ball clays. Hyplas 71 and Hymod AT at £0.90 per kg (25kg bags). Not sure I am in the power or fiberglass industry but they sell it at pottery suppliers
Next are the frits that run from £6-10 a kg (25kg bags). I think they are pretty expensive in the UK.
I went with an Alkaline Frit (similar to 3110 but cheaper) and Ferro Frit 3124, 3134 and 3195 for the glaze and to try in the body.
At 5% frit to ball clay it will cost £1.16-1.31 per kg.
At 10% frit to ball clay it will cost £1.41-1.73 per kg.
At 20% frit to ball clay it will cost £1.93-2.56 per kg.
Looking at that I thought it was definitely worth trying as I could possibly get it under £1.66 a kg. I guess I need to factor in my time making the clay into the cost but if I am planning on casting I feel it would be similar anyway to making a stoneware slip.
I tested each ball clay with 5, 10, 13, 16 and 20% frit in the order Alkaline, 3124, 3134 and 3195. The last 4 tests have a 50/50 mix ball clay to kaolin and 20% of each frit. Fired to cone 03 and then boiled for 5 hours to get the absorption values.
The results actually came out better than I expected with Hymod ball clay and 10% alkaline frit getting to 0.5% absorption at £1.41 per kg I think B0011 I must have messed up as the data doesn't fit.
Colours are sort of accurate in this photo, not a very good camera on my phone.
Now I am experimenting with adding different Calcium Magnesium and Lithium fluxes to see what happens.
Reading that I could have issues with drying times using pure ball clay. It's interesting that the Hyplas has larger particles than Hymod but it is sold as the more plastic, maybe there's something I am missing.
Never did any working out for how much more the glaze costs so maybe that will make things look worse but hopefully it is such a small % total it doesn't make much difference.
- Kelly in AK, Rae Reich, Hulk and 2 others
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Looks like the glaze is full of tiny bubbles and firing a little hotter has let them join together and start rising to the surface. Firing again just let more of them join together so you can see them, I would guess the ones fired in the small kiln are still full of tiny bubbles but they are just hard to make out and look more like a texture.
A lot of gas can be chemically dissolved into the glaze as it melts. As you keep increasing the temperature the chemical solubility of the gas decreases along with more silica arriving into the melt also changing how soluble those gasses are.
I feel whatever you try with different bisque temperatures the glaze will still look the same and produce thousands of tiny bubbles that can't join together and escape because of high viscosity and surface tension
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I always find it amusing that ceramics is 40-50% Oxygen.
Adding more bubbles physically to your glaze shouldn't change how many bubbles your lava glaze makes.
The Silicon Carbide forms Silicon Dioxide and Carbon Dioxide in the glaze and like a fizzy drink you get bubbles. Now I am thinking what could you add to give it more fizz, maybe something like Antimony Trioxide or another oxidising agent.
a bit of method and a bit of madness 
but seems to get lowest around the 30% mark.
An experiment in Fritware Zero3
in Clay and Glaze Chemistry
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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.