Parian Ware Body

[Sputty]

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[Magnolia Mud Research]

If all you need is to have a little more 'shine' on the surface, my suggestion is to spritz the area needing the 'shine' with a solution of baking soda in water at the bone dry stage.   You will be adding 'flux' to the surface where you want the "shine'.  Adding flux to the entire body will weaken the overall structural properties of the piece.

 

This technique works well on bisque ware (that is I know it works).

 

There are early 20th century 'tricks' of using a trailing slip containing baking soda to create a 'shine' on selected areas of otherwise stoneware objects.

 

LT 

[glazenerd]

Agree with LT- frit will weaken the body, and it will not accomplish what you are after. The thought being the fluidity of the frit will rise to the surface; which is incorrect.

Self glazing porcelain is dependent upon the total flux molarity in the body. 3.9% alkali molarity will get you into the vitrified zone @ cone 6. 4.25% alkali molarity will get you into the high glassy matrix (Southern Ice), and 4.90% and above will get you into the self glazing arena.

 

This test bar was over-fluxed (intentionally) Pearl ash was used as the only flux - the alkali molarity was above 7%. Although pitted, you can still see the self glazing sheen; which is what you are after. The recipes you show are 5.00% total alkali molarity and above: which is what you need to reach self glazing.  In a cone 6 porcelain body; you can use sodium or potassium as the main flux; or a combination of both. Both sodium and potassium are in a gaseous state at cone 6 temps: which is what causes it to rise to the surface of the clay; creating the sheen. Frit will not work in the same way mechanically.

 

Both recipes you show are above 5.00% alkali molarity; raising this molarity should produce the self glazing effect you are after. I would start by adding 1% pearl ash, or 10% Mahavir feldspar. The advantage of pearl ash is that it is soluble, and will bleed to the surface as the clay dries to a bone dry state. Usually an unwanted side effect; but in your case a good thing. The draw back to pearl ash is that it greatly increases the PH level of the clay; causing a caustic soda effect: which is tough on bare skin. If you go over 1 percent additions, then you will have to titrate the PH back down because it will cause particularization of the clay. Mahavir is the safer choice, but you will need much more of it. Mica is another choice: it has 13% potassium; not to mention it will greatly elevate the alumina content of the body: a good thing.

 

Usual safety protocols; wear a mask, wear gloves, do not snort mica- etc etc.

 

Nerd

[Sputty]

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[glazenerd]

The detailed response was to give you a frame of reference; some metes and bounds of where you need to take this recipe. I would be looking at the 6% total alkali molarity as a start. Pearl Ash over 2% would be harder on a mold; would be my opinion: knowing its PH properties.

 

Mica does not act the same in a clay body, as it does in a glaze: I frequently use up to 20% mica in clay bodies: it has one of the best alumina sources to strengthen a clay/casting recipe. Assuming you want to cast as large as the example given; high alumina would be a good thing for added strength. Mahavir is imported from India, just assumed Europe would have access: apparently I need to stop assuming. Yes, potash feldspar is what you are looking for: potassium works much better for self glazing applications than sodium.

 

You can also add tin, zirco, titanium, and a host of other elements to the clay body to help further the "alabaster" look you are after.I certainly hope in the future you post some of your work: I find it most intriguing. 

 

I would make 100 gram batches only: and just make simple test buttons. Need to the get the self glazing aspect down first: and it takes very small test samples to accomplish that. You will find that the sides and the top will self glaze; more so towards the top. The part in contact with the shelf will not self glaze at all (gas rises through the body). Understand also, that self glazing porcelain produces just a very thin layer.

 

Nerd

[Sputty]

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[oldlady]

thank you, sputty, for introducing me to the bride.  what a wonderful thing she is.  do you know where she lives?

[Sputty]

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[glazenerd]

 

(I wonder how much further one could stray from Leach, Hamada, etc., in one's pottery interests?)

Come to my studio; and I will show you how far

 

I'm fascinated by the marble - or alabaster - like quality of the work, hence my interest in finding a Parian body.

Find a glaze recipe that produces a warm white, alabaster, or whites in the color range you are after. Make notes of the colorants/ opacifiers used to create those colors. Multiply the main colorants used by 3: add it to your clay. This will give you a starting point. The old testing standard of increasing additions by 2% works when you have already dialed in to some degree. However, when you are testing for the first time with no frame of reference: 10% increases are faster. IE: 5% - 10%-20% -30% etc. When you hit the general area( lets say between 20-40% additions: then you go back to the 2-5% increments. It will save you alot of time trying to dial in on the exact formulation.

 

I don't suppose I'll ever produce sculpture like that, but I have ideas for simpler vessels!

Or you may very well produce one even greater. Da Vinci thought most of his work was poor quality. Not your job to judge your work; that is up to others.

 

Nerd

[oldlady]

the bride is absolutely lovely.  it is really wonderful to have something to aspire to.  it is so tiring looking at modern smeary cobalt glazes and having them called art.  i would rather make a simple, useful single color item that gives pleasure to the user and a smile to his/her face.

 

obviously, i am also one of the dinosaurs.

[Fred Sweet]

Nerd-

-quote-

However, when you are testing for the first time with no frame of reference: 50% increases are faster.

-end quote-

 

This must be a typo. Did you mean to say 10% increases followed by refinement in 2-5% increases after finding a ballpark?

 

50% increases only give you 3 results. 0, 50, and 100% colorant additions.

 

Fred

[glazenerd]

Fred:

 

Wish it was a typo- but mild dyslexia in reality. I get two or three trains of thought rolling around at one time: and one of them ends up derailing. TY for the heads up.

 

Nerd

[Guest]

The Bride is a wonderful piece especially when once you realize the veil is parian. Amazing

[Magnolia Mud Research]

Nerd-

-quote-

However, when you are testing for the first time with no frame of reference: 50% increases are faster.

-end quote-

 

This must be a typo. Did you mean to say 10% increases followed by refinement in 2-5% increases after finding a ballpark?

 

50% increases only give you 3 results. 0, 50, and 100% colorant additions.

 

Fred

 

When conducting screening results for glazes, clay bodies, etc., I use a doubling technique, and change only one variable at a time.

 

A recent example:  I wanted to know what the result was for increasing the amount of rutile added to a base (a clear cone 10R)glaze.  the test protocol was (grams of rutile per 100 grams of base: 1, 2, 4, 8, 16. The results were:

 1 was clear;   2 a pale yellow transparent glaze:   4 was a yellow-orange semi-opaque,   8 was an opaque yellow-orange;   16 was an orange semi-matte.  The screen lead to more detailed line-blends and ended with two new glazes : a "yellow celadon ~2-3 % rutile and an orange semi-matte ~15 % rutile.  Both stable reliable glazes. 

 

The whole test program took 10 test tiles and 2 firings and only 200 grams of test glaze total. For screening it was very efficient and effective.  

 

LT

[Sputty]

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[glazenerd]

 

Silica - 57%

Cornish Stone - 11%

Potash Feldspar - 8%      equals 76%   so I assume 24% was frit?

This recipe I have to assume is some sort of coating. It does not fit into the glaze or clay recipe category. This may very well be the factory equivalent of a spritz; that LT was referencing above. It is a hybrid formula of sorts: if it had more clay I would put it into the porcelain enamel arena. 

 

 

China Clay - 36%

Potash Feldspar - 40%

Frit - 24%

This would be classified as "frit ware" normally, but I suspect they are up to something else. 40% potash feldspar may strike most as a lot, but if is only 10% potassium: so there is only 4% total. China Clay has 3% KnaO, so the bulk of the 10% KnaO alkali molarity in this recipe is coming from the frit. I do believe they may be up to something clever here; something I have not considered... very sneaky..bravo ...... (long explanation required).

 

They are using both chemistry and physics- very good. Frit melts around 1450 F, and potassium @ 800C +/-. 1400F. When you bisq fire a normal clay body it fuses; melts just enough to make the particles stick together. However, when frit is used in fritware: there is a complete mechanical bond around the same temps. That is the starting point of this equation: so now I will add the mechanics (physics).

 

From 2050F to 2190F (1200C) is when the predominate amount of off-gassing from potassium occurs, before it disassociates. Potassium is in a gaseous state, frit is in a liquid state, and the clay is transforming from metakaolin to spinel. (glassy phase). A porcelain body will self glaze if the KnaO level is greatly elevated, forcing the excess gases to be ejected through the surface of the clay- the thin sheen layer deposits. The clay body is transforming from a porous open body (metakoalin) to a closed sealed body (spinel). As the porosity of the body decreases, more of the gas from potassium is ejected: if levels are high enough.

 

HOWEVER: if you add frit (liquid), which has melted and dispersed completely through the body at 1800F (1000C); then the porosity of the body no longer exists because it has been sealed with liquefied frit. This would increase the pressure inside the body, therefore ejecting more gas created from the potassium. (very sneaky-- bravo). So if this body was coated with (the suspected coating shown above); the sheen and thickness of the thin deposit would be denser and more complete.

 

The frit of choice would be critical in this case. Both the glazing sheen formula and the clay body greatly lack in alumina: making for much weaker mechanical structures. So the frit would have to supply the needed alumina in both cases. However, as you noted there is a certain "milky" white appearance to this clay. So I would also suspect they are using a high alumina, zirco based frit. I would do some research into this area of the recipe: I also suspect it makes a critical difference.

 

Nerd

[Pieter Mostert]

Nerd, I'm pretty sure the frit in Sputty's recipe is what you're assuming to be a coating.

 

I would guess that the reason for fritting the mixture of silica, Cornish stone and potspar is to get something that melts more easily and more uniformly in the Parian ware body than if you'd just added it without fritting. If I understand what I've read in various places correctly, the crystalline structure of the feldspars means it takes more energy to melt them than it would to melt the resulting glassy frit. And if you fire the frit mixture high enough, the larger feldspar particles will dissolve completely in the melt, which is unlikely to happen if you just included the unfritted mixture into the Parian ware body.

[Sputty]

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[glazenerd]

Sputty:

 

Language barrier- lets say

 

First, they fritted the following:

Which I took to mean; they added frit to..... instead of made frit from.  Then again, I do not live that far from the Missouri Ozarks. The theory of relativity around here means: "everyone is related to each other."

 

Peter:

I wish I could blame my misunderstanding on drugs and alcohol: but I do not indulge in either. I was discussing "specific heat" last week in the Cone 6 firing schedule. For those interested, these topics would apply to clay:

 

 

https://en.wikipedia.org/wiki/Heat_capacity#Specific_heat_capacity

https://en.wikipedia.org/wiki/Closed_system

https://en.wikipedia.org/wiki/Enthalpy

 

Nerd

 

Sputty: these are the kinds of threads I look for. They stretch your knowledge, make you exercise what you know. Like a giant jig-saw puzzle-- I like a good mystery.