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An experiment in Fritware Zero3

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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 :lol:



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.

1656046732_AbsorptionTable.png.49c954ce84ace688f8167d69b1d2e2f6.png  AbsorptionGraph.png.0762cd982c7fb0bae8cf96597f24be8f.png


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.

Edited by High Bridge Pottery
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1 hour ago, High Bridge Pottery said:

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

Just curious if you considered using a red earthenware and adding frit to that? From Hansen's Zero 3 page he speaks of needing 5% frit added to his earthenware to make it vitreous. Given that the frit is the expensive part of the mix it might be worth testing if you are okay with an earthenware colour. There is an earthenware available here that when fired to cone 04 has porosity at 6.0% but when fired to cone 02 porosity goes down to 1.5%,  anything like that where you live?

Nice experiment work!

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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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3 hours ago, High Bridge Pottery said:

Need to add something to speed up drying and keep it melting.


Since you have kaolin why not cut the ball clay with that?

3 hours ago, High Bridge Pottery said:

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.

On this side of the pond aiming for under 1 1/2% absorption is pretty common for pots that shouldn't weep. 

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Very interesting! Thank you for sharing. I'd shoot for below 1.5%. 3% will probably still weep. I agree, try some kaolin. It should speed up drying and increase whiteness. Have you done any tests to figure out how low you'll have to bisque fire in order to get suitable porosity for glazing?

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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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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 B) 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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Electric at .5 £/kwh is about $0.61 (US dollars), wow.
In Central California, off-peak Winter is just over $0.28/kwh (was 34¢ in Summer).

HBP, do the graphs depict percent absorption (water) by weight (vertical) for each trial (horizontal)?
If so, that's some good results!

I went with petalite (to lower liner glaze COE), cheaper per unit lithium (and avoiding the reported Spodumene foaming). Am seeing some small grey specks, but I don't mind them.


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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 :blink: 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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What's the going price for spodumene where you live?(or the lithia equivalent amount of petalite) I can get a 50lb bag of 3110 frit for $215 (Canadian dollars) vs $392 for 50 lbs of spodumene. Petalite is a bit cheaper but since you need more there isn't savings.

I used a claybody years ago that had wollastonite in it that I really liked except it irritated my hands so much I had to give it up. Think it was because of the wollastonite particle shape.

Thanks for sharing your testing, interesting results.

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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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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 :mellow: 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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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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I appreciate your methodical approach. I rarely use unity, it is certainly useful though. For me it tends to serve as a reality check or troubleshooting aid. I’m a long way from mastering that tool, but glad it’s in my toolbox. Your picture above is a nice illustration, two mixtures with similar chemistry behaving very differently. 

My armchair reasoning is you’ve got the issues of: Hymod clay really holding on to water, trying to get the clay vitreous using as little frit as possible, and using materials that are readily available and not too expensive.

I’ll throw in some thoughts from my perspective, for fun. Between b0073 and b0010, I feel like 73 doesn’t have enough frit to make the neph sy go into melt. 10 has too much plastic material to dry at a reasonable speed (I am amazed that one got so tight with just 20% frit though! Powerful stuff.) I jumped to figuring how to split the difference in a useful way (60 ball clay, 30 neph sy, and 10 frit was where my brain landed). 

 I feel the same way about introducing silica as an additional ingredient, getting the body to play right then tuning glaze and/or body if there are problems with fit. All your materials have significant silica built in.

Anyway, I enjoy you giving us this window to watch the journey unfold, I’m learning a lot. 

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Thank you :D a bit of method and a bit of madness :lol: 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 B)

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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Kaolin should reduce drying time quite a bit, but it will probably increase the porosity, too. Personally, I would be very interested in seeing a body that was all kaolin/no ball clay, to see how much the color of the body is affected.

As a kiln tech guy, the most exciting part about this is the potential for really good element life and kiln lifespan while still making vitrified ware. It's something I've though about a lot, but never had the time to pursue. It would be really bad for my kiln sales and repair business, though! I used to fire at cone 8, and by dropping to cone 6, which is only a difference of about 50 degrees, my element life increased by 25-30%. By dropping from cone 6 to even cone 1 would make a huge difference. This is exactly what clay and glaze manufacturers should be working on as energy costs and kiln costs continue to rise. On that note, why cone 03? Is that the limit of your kiln? Have you though about taking one of your tests that is at around 2.5% absorption and going 1-2 cones hotter to see what happens?

I'm also excited to see how glaze fit works in these bodies when you get to that point. I have to think you'll get a much better clay/glaze interface than with typical porous earthenware bodies.

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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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