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glazenerd

Flux Formula Limits For Porcelain

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Thanks Nerd, great stuff and thanks for sharing.

 

Agree that fluxes must be approached from a molar perspective. Given the variable composition of the materials we all use, simply adding some weight percentage "feldspar" is like throwing darts in the dark. Software is critical when you want to go past a certain level in this game.

 

Also agree I have found in my own clay body testing that particle size is critical, and it was some of the discussion you generated some months back in some of your earlier posts on silica that got me thinking about this.

 

A couple of follow on questions:

 

1. How does Ph adjustment resolve pin holing problems?

 

2. How do you eliminate the solubility problem with potassium when using it as a body flux?

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Fascinating!

 

Do you have a ball-park figure for how much vinegar you are adding? (I'm interesting in working out

the final carbonate:acetate ratio).

 

PS

Are you familiar with drop moulds, they might minimise surface disturbances when forming (fun to use too).

 

glazenerd likes this

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Being soluble, does the pearl ash migrate to the surface as the piece dries, like soda ash does? How are you using the clay- slabs, throwing, etc? I'm wondering how the pearl ash and vinegar affect plasticity.

 

Me too.

 

best,

 

...................john

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Peter: originally I was using 1/2 liter of vinegar to 6.5% (recipe weight) of pearl ash. 5.77% total alkai. The I tried diluting 1 cup muratic (20% hydrochloric) acid in one gallon of water. Then finally I used oxalic acid solution. Now I am down to 2% pearl ash, in a combination with mahavir potash: in this combination I only use 1/4 cup of oxalic or very diluted muratic to adjust the pearl ash down to 8.5PH before mixing.

 

Neil & John: in the first batch: I did notice white patches forming after the clay would rest for a day. I mixed it several times over the course of blending. I did not notice those patches before I rolled it out for tile )or after. The fired results were great; did not note any adverse effects. I did however have an unusual reaction when I used pearl ash in conjunction with mica: scumming when wet, and felting when fired to maturity.  My tile formula has little plasticity to begin with: so I cannot gauge a response to that question. Not sure after the initial batch, if by adding vinegar it also effected migration issues.

 

I have noticed since first adding 2% T gum that the clay is still very grainy: not as plastic as I would have expected. I am not sure how much of that is vinegar, and how much of that is a high ratio of heavy particle clay. I mixed a second 1000gram batch this morning: using macaloid this time. If tackiness is any measure of plasticity: then it is highly plastic.

 

Nerd

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Neil:

 

1. Standard absorption test: primarily for vitrification.

2. Shrinkage test: common bar length measured green, bone dry, bisq, and mature. ( Coma is 10% exactly.)

3.Thermal shock: throw one of the boiling test bars into the freezer. Have also heated them up to 400F and dropped into cold water.

4. I use acid to test vitrification/silica levels. I have soaked test bars in pure muratic and sulfuric for up to a month. If it decomposes at all: then silica levels are probably low: acid will not attack glass.

5. Poor mans MOR test. I have an old drill press with 1/16th depth gauge. I support each end and leave the middle unsupported. I simply slowly bare down until it breaks. Not scientific: but it gives me some indication of strength.

 

I have a host of other methods of testing plasticity, etc.

 

Already spoke to the alumina % above for strength: both green and fired. Silica also adds strength via the glassy matrix it forms in the mature body. When using heavy particle size clays, it becomes more important to ensure it is completely bonded.

 

I am surprised that no clear set of formula limits exist for clays: primarily porcelain. I think it was bypassed by and large because most just buy it, or use variations of proven recipes.

 

Nerd

 

There are other parameters involved that I will not post: but they are strictly in line with developing a body that is conducive to crystal development.

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I am surprised that no clear set of formula limits exist for clays: primarily porcelain. I think it was bypassed by and large because most just buy it, or use variations of proven recipes.

 

 

 

Bingo. Most folks who don't produce in large volume are typically not trained in formulation and don't have the necessary equipment. Those that do produce in volume know what a pain it is. Some things are best left to those who are set up to do it easily and safely. You, of course, have very specialized needs. However once you get it figured out, you could always have someone mix it for you.

 

Given all of your tests, at some point you'll have to make some concessions in certain areas. For instance, I'm willing to give up a little glassiness in exchange for reduced warping. Is crystal development your primary goal? 

 

Thanks!

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Nerd-

You said:

"Already discussed formula limits for whiteness in the Porcelain Survey thread. For ultra white body that will not discolor any glaze including clears: MGO less than 0.30% and FE less than 0.50% molar. TiO2 are not as critical: but I stay well under 1.00%"

I'm at a loss for why you want to worry about magnesium oxide (MgO). Or were you wanting to limit manganese oxide (MnO) to less than 0.30%?

Respectfully, but with some confusion,

Fred

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Fred:

It is common knowledge that glaze will leach materials from the clay body. Potters rely on their glazes leaching alumina to prevent glaze flow. However, glaze will also leach iron (FE), magnesium (MgO), and titanium dioxide (TiO2.) Anyone who has applied the exact same glaze to porcelain and then stoneware have seen the dramatic differences in outcome. Stoneware clays are noted to have high iron, and some have high magnesium content. The iron will turn a bright yellow glaze on porcelain to a much duller yellow on stoneware. For those reasons I stated for ultra white porcelain that will not alter clears or other pastels glazes: iron and magnesium must be held below these limits. >MGO less than 0.30% and FE less than 0.50%

 

MGOFE

 

Bar 1 MGO 0.33 FE 0.32  TiO2 0.37   Bar 2 MGO 0.89 FE 0.36 TiO2 0.74   Bar 3 MGO 0.78 FE 0.42 TiO2 1.16   

 

Bar 4 MGO 0.42 FE 0.36 TiO2 0.69    Bar 5 MGO 0.63 FE 0.32   TiO2 ??   Bar 6 MGO 0.49 FE 0.40   TiO2 0.60                                                                             

Bar 7 MGO 0.36 FE 0.86 TiO2 0.39    Bar 8 MGO 0.42 FE 0.74  TiO2 0.79  Bar 9 MGO 0.97 FE 0.91 TiO2 3.77                                                                                                                             

Control Tile- top MGO 0.18 FE 0.32  TiO2 0.22     (all tests fired in oxidation)

 

Notice test bars 2 & 3: the gray cast is from excessive MGO levels. This will ultimately leach into a clear glaze and discolor it.

 

 

neilestrick

Bingo. Most folks who don't produce in large volume are typically not trained in formulation and don't have the necessary equipment. Those that do produce in volume know what a pain it is. Some things are best left to those who are set up to do it easily and safely. You, of course, have very specialized needs. However once you get it figured out, you could always have someone mix it for you.

Had the feeling I was stepping out into uncharted territory by the lack of info out there. Ron sent me an email a few weeks back telling me to publish my findings. I told him maybe 50 people worldwide would even care enough to buy a book. Yes, my primary goal is for crystalline glaze: but have been discovering some tricks along the way.

 

Nerd

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Let me add some more information for porcelain formulation: got side tracked on pearl ash.

 

The flux of choice plays a role in melt, in temperature range: but also in raising the COE of the body. One of the problems encountered with using porcelain is aligning the COE of the glaze to the COE of the clay. Flux percentages can elevate the COE, but adjustments in silica can also be used for that purpose.

 

50% EPK

25% silica

25% Nep Sy. COE (est.) 5.77

 

50% EPK

25% silica

25% Mahavir COE (est) 5.54

 

 

50% EPK

22% silica

28% Nep Sy. COE (est) 5.96

 

With just a simple adjustment in silica and flux: the COE values raise.

To increase those values further, and to add the benefit of thermal expansion: replace part of the silica with pyrophyllte:

 

50% EPK

11% silica

28% Nep Sy.

11% pyrophyllte COE (est) 6.05

 

This simple change in recipe increases the COE, but also adds thermal expansion values. This formula would work better for raku firings, ovenware, or other applications were thermal shock would be an issue. However, pyrophyllte has a second added benefit that is not addressed from my research into it.

 

Nerd:

 

For the record: macaloid works better in porcelains for several reasons. V-gum T works just as well, but has the additional step of blunging. However, if you want to add body stains or oxides for colorants: blending them into a V-gum T solution prior to adding to the dry materials: it would disperse the materials much more uniformly.

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Ron sent me an email a few weeks back telling me to publish my findings. I told him maybe 50 people worldwide would even care enough to buy a book. Yes, my primary goal is for crystalline glaze: but have been discovering some tricks along the way.

 

Nerd,

 

I was about to suggest the same thing as Ron.  You are into research that is certainly publishable.  And don't underestimate the importance of publishing this stuff.  There are crystalline glaze people (if no one else) that will really appreciate the information and the work.  I'd suggest contacting Elaine Henry and "Ceramics Technical" to see if they are interested in the piece.  That is a n international journal and focused on more technical ceramics stuff.

 

best,

 

..........................john

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Well John: now I feel all humbled. Was only trying to formulate the perfect crystalline clay: who knew? Have several more posts full of information that I have not gotten to yet: not sure what to do now. One of the more important being: diagnosing results.  Clay talks if you know what to listen for. Maybe the Daily section would be interested: would feel much more comfortable there. Besides: this has sorta become my clay home.

 

Nerd

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Nerd,

 

I think that what you are doing fits more in a venue like I mentioned.  The readership / audience is there in that publication.   Less so CM / PMI / CAD.   Yes... they do some tech.... but not like what you are into.

 

best,

 

....................john

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(Sorry messed up the quote, but some questions below Nerds original here at the top)

 

quote name="glazenerd" post="112417" timestamp="1472782948"]Fred:

It is common knowledge that glaze will leach materials from the clay body. Potters rely on their glazes leaching alumina to prevent glaze flow. However, glaze will also leach iron (FE), magnesium (MgO), and titanium dioxide (TiO2.) Anyone who has applied the exact same glaze to porcelain and then stoneware have seen the dramatic differences in outcome. Stoneware clays are noted to have high iron, and some have high magnesium content. The iron will turn a bright yellow glaze on porcelain to a much duller yellow on stoneware. For those reasons I stated for ultra white porcelain that will not alter clears or other pastels glazes: iron and magnesium must be held below these limits. >MGO less than 0.30% and FE less than 0.50% molar

 

 

 

Bar 1 MGO 0.33 FE 0.32 Bar 2 MGO 0.89 FE 0.36 Bar 3 MGO 0.78 FE 0.42 Bar 4 MGO 0.42 FE 0.36

Bar 5 MGO 0.63 FE 0.32 Bar 6 MGO 0.49 FE 0.40 Bar 7 MGO 0.36 FE 0.86 Bar 8 MGO 0.42 FE 0.74

Bar 9 MGO 0.97 FE 0.91 TiO2 3.77 Control Tile- top MGO 0.18 FE 0.32 (all tests fired in oxidation)

 

Notice test bars 2 & 3: the gray cast is from excessive MGO levels. This will ultimately leach into a clear glaze and discolor it.]

 

Hi Nerd,

 

I will be the first customer to buy your book.

 

Very interesting and great to have the photos. As someone who also spends a fair amount of time testing I appreciate how long it takes to produce these samples while you could have been doing something else in the studio, so thanks for your efforts.

 

Did you arrange the bars in this order for a particular reason? I find it a bit challenging to seperate the effects of MG and Fe when they are both moving at the same time. However, that said, comparing the control disc with bars 1 and 5 is interesting, because for those three Fe is fixed but Mg is increasing. Bar 1 looks a familiar creamy iron yellow white, but bar 5 looks a greyish white. Not sure if it is darker than bar 1, but it's shade definitely seems to be moving in the direction of bars 2 and 3.

 

Do you have the molar Titanium for each of these bar samples? I agree that Titanium is important and most everything I have read says that it is the combination of Titanium and Iron that is important in keeping clay white.

 

This is the first time I have seen Mg implicated, but now I will now go back and look at some of tests with this in mind.

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Nerd: Peter: originally I was using 1/2 liter of vinegar to 6.5% (recipe weight) of pearl ash. 5.77% molar.

 

Nerd, I need to know the recipe weight to work out how much bicarbonate you have neutralised.

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Peter:

The pearl ash is part of my Coma Clay tile recipe, that will remain proprietary. I do not mind sharing (most) everything I have learned and discovered along the way: but that one will remain secret. Secondly, 80% of the kaolin/s involved in that recipe are not sold in the clay arts supply chain and the specs are not readily accessible.

However, I have been using the simple recipe of 50% EPK, 25% silica, and 25% Nep Sy for illustration purposes: and your offer would help clarify the effects of acidic titration. Although that recipe would have to change to 65% EPK, 25% silica, 6.5% pearl ash, and 3.5% L10 bentonite

Nerd

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Peter:

The pearl ash is part of my Coma Clay tile recipe, that will remain proprietary. I do not mind sharing (most) everything I have learned and discovered along the way: but that one will remain secret. Secondly, 80% of the kaolin/s involved in that recipe are not sold in the clay arts supply chain and the specs are not readily accessible.

However, I have been using the simple recipe of 50% EPK, 25% silica, and 25% Nep Sy for illustration purposes: and your offer would help clarify the effects of acidic titration. Although that recipe would have to change to 65% EPK, 25% silica, 6.5% pearl ash, and 3.5% L10 bentonite

Nerd

 

That's fine, no problems. However if I'm to calculate how much of the bicarbonate is neutralised I need to

know how much bicarbonate was in the mixture you added the vinegar to.

 

I don't see how telling me  this directly (in gms of pearl ash) or indirectly (as the weight of the "batch of dry

ingredients" you added 6% pearl ash to) would compromises any secrets you wish to keep secret.

 

Regards, Peter

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Then there is particle size distribution in the body....

 

Nerd,

 

As I was reading the above I was just going to ask you if you have explored the concept of packing density........ and here you end with this line!  :)

 

best,

 

......................john

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This is a fascinating thread.

I've also been under the impression that iron and titanium are the main things to control for whiteness. Is it possible that one of the ingredients in the grey test bars has an incorrect analysis? What makes me doubt magnesium as the culprit is that Macaloid is about 22% MgO by weight (apparently Veegum T is similar). In a 50% Kaolin, 25 Neph Sy, 25 Silica body, 1% Macaloid contributes about 0.4% molar MgO. If you're adding 2% Veegum T, shouldn't all your tests be grey?

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