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AnnaM

Self Glazing Cone 04 Porcelain

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Hi all,
I'm new to the forum so hoping someone has some knowledge on this!
After seeing Justin Rothshank's recent work I started looking into finding a similar clay body and I've found a published paper which has a recipe and firing schedule for self glazing porcelain that vitrifies at 1050°C.
This seems to me to be just too good to be true (fingers crossed that it is true!) Does anyone know anything about this? If the recipe is out there why would clay manufacturers not be making and selling this self glazing low fire porcelain?

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Bone china fires to a gloss surface.  It's not that unusual.  But it's not a glaze or a color, just fully vitrified.

 

Anorthite is a calcium rich silicate, a feldspar in other words. 

 

It looks like this - at least this Anorthite sample from the Moon brought back by Apollo does.

 

anorthosite_1.jpg

 

It could be a beautiful glaze to some.

 

Hi all,
I'm new to the forum so hoping someone has some knowledge on this!
Are seeing Justin Rothshank's recent work I started looking into finding a similar clay body and I've found a published paper which has a recipe and firing schedule for self glazing porcelain that vitrifies at 1050°C.
This seems to me to be just too good to be true (fingers crossed that it is true!) Does anyone know anything about this? If the recipe is out there why would clay manufacturers not be making and selling this self glazing low fire porcelain?

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The frit appears to be high in levels of low-temperature flux potassium along phosphorous and silica which are ingredients in a bone china.

 

By themselves the Wollastonite (Calcium Silicate) and Kaolin (aluminum silicate) have melting temperatures which are too high.

 

Unfortunately all of the commercial frits I'm aware of with high levels of Potassium, also have high levels of Sodium which gives the procelain body too much expansion - like Laguna New Zealand Frost.

 

Perhaps someone else knows of a frit with just calcium and potassium flux.

 

Is that frit in recipe close to any commercially available frit?

Making clay is ez. Why depend on mfgr.

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Saw a post on ClayArt that said: There is a description of a high potash frit made from pearl ash, feldspar and kaolin in Michael Cardew's "Pioneer Pottery", page 144 to 148. He writes that it "breaks all the rules of frit making" and uses it to make a bright iron red glaze. 

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There's no way to come close to K2O:B2O3:SiO2 in a ratio of 1-2-3 or 17% K2O,  33% B2O3, and 50% SiO2. - except to use Pearl Ash, Boric Acid, and Silica to make your own frit.

 

G200-HP Feldspar is a mere 13.2% K2O.  Yet the materials they describe using to make the frit, in the abstract, contain no Boron - just Pearl Ash, Silica and Phosphoric Acid. But in the paper itself they use a different formula which includes Boric Acid and excludes Phosphoric Acid - a mistranslation from Turkish?

 

 

Potassium sure brings out colors.  And using isoelectric Aluminum Phosphate in equal molar amounts, in place of Silca, brings out reds in iron red.

 

Interesting but I know of no commercial frit matching this make-up. 

 

I might try putting the raw materials into the next firing in an alumina crucible to see what happens, as I have no other heating source.

 

Saw a post on ClayArt that said: There is a description of a high potash frit made from pearl ash, feldspar and kaolin in Michael Cardew's "Pioneer Pottery", page 144 to 148. He writes that it "breaks all the rules of frit making" and uses it to make a bright iron red glaze. 

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Norm posted .. using isoelectric Aluminum Phosphate in equal molar amounts, in place of Silca, brings out reds in iron red.

 

Very intriguing result Norm.

 

- Is there any additional information available, apart from your own web page

  http://cone6pots.ning.com/photo/magruder-red-with-aluminum-phosphate-no-silica

 

- ... including the use of aluminium phosphate in types types of glaze, as suggested at the end of the

  page on Magruder Red.

 

- Could you achieve similar effects supplying the aluminium and phosphate from different sources?

  I ask because I believe that crystalline potassium [or sodium] metaphosphate is highly insoluble.

  http://pubs.acs.org/doi/abs/10.1021/ie50362a020

  Which sound like an interesting way of making hi-potassium glazes (if the phosphate ion doesn't

  cause trouble). 

 

Regards, Peter

 

PS The solubility of the phosphate may be more like that of hi-alkali frits, as it can be used as a slow-release fertilizer.

 

PPS Another of Norm's pages on aluminium phosphate

http://cone6pots.ning.com/photo/berlinite?commentId=2103784%3AComment%3A86474&xg_source=activity

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Sorry this all Greek to me! What I was wanting to know specifically is:

 

1) is this likely to be a foodsafe clay body?

2) does it sound plausible that it would truly be vitrified at cone 04?

 

I'd like to try it but don't have the faintest idea whether it sounds plausible, and if (to someone more experienced than I) there is something glaringly odd about it, I'd rather wait till I have more money to potentially waste if there's a fairly big chance the exercise would be in vain :)

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I simply mixed 85% phosphoric acid with "Alumina Hydrate" to get the starting base of hydrated alumina phosphate.

 

You have to keep track of how much you started with to know how much Aluminum Phosphate there is in the hydrate. Because if you try to dry it out it becomes a cement which adheres to glass or ceramic, so I just added it to the glaze as the hydrate.

 

At the time I was trying to add phosphorous to glaze without adding calcium (ie bone ash) for red iron glazes.  The end result for red iron glazes was starting with pure red iron oxide instead the witches brew of iron, barium and other recycled metals I had obtained from Laguna Clay as red iron oxide.

 

It's cheap to buy aluminum phosphate as the powdered sodium aluminum phosphate, which is a food additive - but you're stuck with the extra sodium which raises the COE.  It's tougher to get potassium aluminum phosphate, but for that use I didn't want the potassium wither.

 

Starting with potassium metaphosphate seems like an ideal source ingredient for what AnnaM is trying to do.

 

That's a great idea Peter.  A lot of glazes you wouldn't expect benefit from both potassium and phosphorous.

 

Norm posted .. using isoelectric Aluminum Phosphate in equal molar amounts, in place of Silca, brings out reds in iron red.

 

Very intriguing result Norm.

 

- Is there any additional information available, apart from your own web page

  http://cone6pots.ning.com/photo/magruder-red-with-aluminum-phosphate-no-silica

 

- ... including the use of aluminium phosphate in types types of glaze, as suggested at the end of the

  page on Magruder Red.

 

- Could you achieve similar effects supplying the aluminium and phosphate from different sources?

  I ask because I believe that crystalline potassium [or sodium] metaphosphate is highly insoluble.

  http://pubs.acs.org/doi/abs/10.1021/ie50362a020

  Which sound like an interesting way of making hi-potassium glazes (if the phosphate ion doesn't

  cause trouble). 

 

Regards, Peter

 

PS The solubility of the phosphate may be more like that of hi-alkali frits, as it can be used as a slow-release fertilizer.

 

PPS Another of Norm's pages on aluminium phosphate

http://cone6pots.ning.com/photo/berlinite?commentId=2103784%3AComment%3A86474&xg_source=activity

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Anna  - The answer to food safe ceramic body or glaze is always, do a leeching test.

 

If I were to guess, this appears to end up as vitrified glass (aka self-glazing ceramic and the ceramic is glassy) so should be perfectly food safe - but always test.

 

But you have to figure out what this translated Turkish article is calling for, because the body of the paper calls for different ingredients from what the abstract mentions.

 

There's no ceramic frit I know of which contains this particular mix of material.  So if there isn't already a frit for dental use with this make-up Peter's suggestion of potassium metaphosphate is an alternative starting ingredient to what I've suggested. 

 

Sorry this all Greek to me! What I was wanting to know specifically is:

1) is this likely to be a foodsafe clay body?
2) does it sound plausible that it would truly be vitrified at cone 04?

I'd like to try it but don't have the faintest idea whether it sounds plausible, and if (to someone more experienced than I) there is something glaringly odd about it, I'd rather wait till I have more money to potentially waste if there's a fairly big chance the exercise would be in vain :)

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Hey up! Norm is right that there seems to be an inconsistency.

 

The paper's abstract mentions 43.8% H3PO4

... and then goes on to mention the K2O:B2O3:SiO2 ration (Boron not Phosphorous).

 

The ingredients used (1st para section 2) mentions Boric acid (H3BO3), but not phosphoric acid (H3PO4).

 

The preparation of the frit (1st sentence 2nd para section 2) gives 43.8% H3BO3.

 

Table 1 has a column for  B2O3, but not one for P2O5.

 

... so my guess would be that the initial mention of H3PO4 is some sort of spell-checker assisted typo.

 

IMHO there is no phosphorous, just boron.

 

Back to you Norm for advice on a suitable boron frit.

 

Regards, Peter
 

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Since Anna says they use this in dental work there may be a frit sold for dental labs, but there's no frit with this make-up being sold through art ceramic channels.  So it would be a matter of melting the soluble ingredients to make your own frit.

 

Hey up! Norm is right that there seems to be an inconsistency.

 

The paper's abstract mentions 43.8% H3PO4

... and then goes on to mention the K2O:B2O3:SiO2 ration (Boron not Phosphorous).

 

The ingredients used (1st para section 2) mentions Boric acid (H3BO3), but not phosphoric acid (H3PO4).

 

The preparation of the frit (1st sentence 2nd para section 2) gives 43.8% H3BO3.

 

Table 1 has a column for  B2O3, but not one for P2O5.

 

... so my guess would be that the initial mention of H3PO4 is some sort of spell-checker assisted typo.

 

IMHO there is no phosphorous, just boron.

 

Back to you Norm for advice on a suitable boron frit.

 

Regards, Peter
 

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Ok, so it basically will be a more glassy clay body? Sounds promising? Which would make sense as far as dental porcelain goes as lower porosity would mean less leaching wouldn't it?

 

What would that be likely to do to plasticity and workability?

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Hi Anna

 

Was experimenting with this during my undergrad about 12 years ago......

 

Pick up a copy of Sue Peterson's 'The Craft & Art of Clay'', page 381 gives a recipe for ^04 low fired porcelain and page 152 has a recipe for a ^04 Irish 'Belleek' style porcelain.......both came out as a warm white, glassy body with a soft satin sheen. 

 

Being a 2nd year student and not that interested in formulas I used the frits I had on hand, in my case lead bisilicate, but the recipe can also use ground glass which I got from a bottle recycler.

 

Hope this helps.

 

Irene

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When the only plastic material is 50% kaolin, a lot is going to depend on the plasticity of the Kaolin you choose.  EPK from Florida is more plastic with most, being a small particle size kaolin.  But if you EPK you'll want to try replacing some of the EPK with Vee-Gum bentonite, even though EPK is more plastic than most kaolins, as the frit and Wollastonite don't have any plasticity - although Wollastonite is naturally compressible and fibrous. Using 45% EPK and 5% Veegum might a good place to start.

 

http://digitalfire.com/4sight/material/ep_kaolin_291.html

http://digitalfire.com/4sight/material/veegum_1672.html

 

Another choice is PVC (Plastic Vitreous Clay or Plastic Vitrox) which is slightly fluxy with 5% potassium like a feldpar.  You might end up eliminating part of the potassium in your frit.  http://digitalfire.com/4sight/material/pv_clay_1152.html

 

More plastic kaolins are mined in France and New Zealand.

 

Susan Peterson's ^04 porcelain uses ball clay to create the plasticity, so it fires less white.

25%  China Clay
25%  Ball Clay  (OM4)
40%  Ferro Frit 3110
10%  Silica
 

 

Generic China Clay is not very plastic at all, so you could probably use a more plastic kaolin and reduce the amount of ball Clay.

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Thanks Norm. I ended up making about 500gms to test out a recipe of 50% Frit (I used Ferro 3/4110), 25% ball clay, 25% Kaolin. It was not very plastic at all, but throwable - very gently and slowly!

 

I threw a decent cup out of about 250gms of it which is drying now and the other half of it, Im letting dry out a bit more to see if it's a bit easier for me to throw when it's a bit harder.

 

I've got a couple of recipes to try tomorrow, and I'll try Susan Peterson's as well. I'm quite encouraged by Irene's experience!

 

Will post results as they are fired ;)

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Hi Anna

 

I only threw with the clay twice and yes it wasn't very plastic, was a bit better for smaller handbuilding shapes but couldn't hold its own wieght in taller forms.

 

I used it for slip casting and got variations on off-white or cream depending on the kaolin/ball clays used but for some things the warm colour was quite beautiful. Don't know the Australian/US equivalents of the clays so can't recommend one.

 

The high frit content meant some of the forms would soften a little in the firing especially if thin cast and/or when pushed to to ^03 (1100C) and in some cases when pushed to ^02 would gently collapse in on themselves looking like soft fabric folding....very beautiful for sculptural applications I thought.

 

Hope your experiments are going well, post some pictures!!

 

Irene

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I've got the results of 4 batch tests cooling down in the kiln as we speak! I'll post the photos tonight.

 

One thing I've learned in the last few days is that I will never take plasticity for granted again! I started feeling like I couldn't throw and had to mix up a few hundred grams that was only ball clay and Frit to prove to myself that I still could!

 

The whole reason that I wanted to try this was because my little kiln only gets up to Cone 03, and I need a body that will vitrify at that low temperature. The ball clay I've used is quite a greyish one and (in order to get a whiter clay body) was wondering whether adding Frit to my fine white earthenware clay would lower it's vitrification point? Does that sound like a silly idea? Is there any reason you couldn't muck around with a pre-mixed commercial clay?

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