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Help Needed with Glaze Recipe - MarieP

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On 6/1/2019 at 9:58 AM, Min said:

Hmmm, for a clay to be mature from ^04 through to ^10 is impossible. It will be vastly immature at the low end or overfired at the top. Flux levels in the body can't satisfy such extremes in firing. Even bodies claiming to go from ^6 - ^10 is problematic, chances are it will leak at ^6 or bloat / slump / over vitrify and become brittle at ^10. Better to use a midrange clay for 6 and a highfire clay for 10. Are you planning on firing to both 6 and 10 and looking for one glaze to fit both?

 

Screenshot below of what the chemistry would look like for a glaze with 50 colemanite, 50 epk, 15 zircopax plus 2 bentonite. Next to the recipe is a "limits" chart that shows the range (Rge column of the pink box) of each oxide required to produce a durable glaze. Many glazes have figures outside these ranges but they are guidelines. What is really important to look at are the silica and alumina levels. When these are too low the glaze won't wear well and any heavy metals in the glaze have a far greater chance of leaching out of the glaze. Boron is far too high, excess boron makes a "soft" glaze and can actually promote crazing. Another important thing to look at is the R2O : RO flux ratio, it's way off in this recipe, there are no R2O fluxes in this glaze, this will also contribute to a very non-durable glaze.

1437789198_ScreenShot2019-06-01at9_42_52AM.png.449f4743902dfc55a9337af556bb47ea.png

Hope this helps clarify what some of the concerns are with this glaze. Lots of recipes that are much better than this one.

 

Then the missing 50 is not EPK.  The properties everyone keeps describing on here are not present in this glaze.  It is not fussy in any way.....doesn't run, matures everywhere in the kiln just fine, does not craze and is durable   So EPK is incorrect. 

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On 6/1/2019 at 10:34 PM, Bill Kielb said:

I think stroke and coat generally performs 04-10 as fully melted. Advertising as you say cone 04 bisque for a glaze would be very confusing in my view. How do they advertise their low fire stuff?

7C030A66-3B4F-4C47-B7AC-82EA8A815876.jpeg

My observations of these is that they behave more like a fluxed, glossy underglaze. I know people that work with them at cone 06 as underglaze, but apply a clear glaze overtop as they're a bit dry if you're trying to get those detailed brushstrokes they talk about. I've seen them taken to cone 10 reduction, but all the pinks, yellows, reds, oranges etc. burned out, as one might expect. They don't run, though, and they do behave more glaze-like the thicker they're applied. They're kinda spendy though, so probably not something you'd want a big bucketful of for dipping.

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40 minutes ago, Callie Beller Diesel said:

My observations of these is that they behave more like a fluxed, glossy underglaze. I know people that work with them at cone 06 as underglaze, but apply a clear glaze overtop as they're a bit dry if you're trying to get those detailed brushstrokes they talk about. I've seen them taken to cone 10 reduction, but all the pinks, yellows, reds, oranges etc. burned out, as one might expect. They don't run, though, and they do behave more glaze-like the thicker they're applied. They're kinda spendy though, so probably not something you'd want a big bucketful of for dipping.

My hunch is they are just cone 04 glazes with sufficient silica and alumina to make it to cone ten. I have some old recipes that have excessive boron but high silica and alimina. They melt pretty decent at 04 but hang in there to cone 10. They are glazes though so real glass formers and flux. My suspicion for the above would be mason stain type colorant so same issue with color variance as the temperature increases. I do like them over the top of glazes as decoration and fire down though, just like low fire glazes. Made some nice textured fire breathing dragons that way with more texture than China paint.

Edited by Bill Kielb

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On 6/1/2019 at 11:49 AM, Pieter Mostert said:

Was the unknown ingredient Plastic Vitrox clay? Sounds like it might be this recipe: https://glazy.org/recipes/2875

Be aware that the analysis in glazy uses the theoretical composition of Colemanite (https://glazy.org/materials/15119) whereas what's actually sold may have a different composition, for example https://glazy.org/materials/37220 or https://glazy.org/materials/20787

If the 35 year old piece is functional and has been in use for most of its life, I wouldn't worry about any theoretical durability concerns.

Upon reflection, I think you are correct.

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Here's a friend recipe that will maybe work for you its cone 10 soft fired

Here’s our base glaze—could just call it Satin Matt, I guess.  Doesn’t exactly come out to 1000 gram batch, but oh well!

Custer 347

Dolomite 196

Whiting 31

EPK 247

Silica 227

1 percent tin oxide

5 percent zircopax

 

You can paint any colorants over it you like as well

Edited by Mark C.

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On 6/1/2019 at 6:27 PM, Denice said:

A glaze that looks good at any cone will only be functional at the highest cone.   Fired at C 6 in a electric kiln it wouldn't have any iron spots and would leak fluids through the glaze.  You could put a  C 6 liner glaze inside of a mug or pot to solve this problem.  There has been a lot of changes in glaze formulations in the last 35 years.  These changes are do to many different reasons,  such as gerstley borate  is no longer available not enough left to mine.    You can get some great glazes from the glaze guru's on the forum.  If you are fining oxidation at C6  speckled buff is a great clay that gives your iron spots.    Denice

Gerstley borate is available through Laguna clay and their distributors. 

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On 6/12/2019 at 7:56 PM, Mark C. said:

Here's a friend recipe that will maybe work for you its cone 10 soft fired

Here’s our base glaze—could just call it Satin Matt, I guess.  Doesn’t exactly come out to 1000 gram batch, but oh well!

Custer 347

Dolomite 196

Whiting 31

EPK 247

Silica 227

1 percent tin oxide

5 percent zircopax

 

You can paint any colorants over it you like as well

Thanks Mark!

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I bought some of the Gerstley Borate from a Laguna dealer probably 10 years ago,  my dealer told me it was being dug from a different area of the pit.  He said it wasn't exactly the same chemical composition of the original Gerstley Borate that I was  using.   He said the some of my Gerstley  based formulas may not have the same results.   I don't think this is a big problem in C10 reduction glazes but any chemical change in a oxidation C6 glaze can cause havoc.  Denice

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Gerstley not really essential for cone ten.  The deposit Laguna has was in storage at the mine.  Nothing is being dug, it’s primary consumer was the military for underground nuclear testing.  The mine has been closed for many years now. They discovered the mined material on site,  purchased it, and certified it’s composition in 2011. See attached. So it has been roughly this way for quite some time.  Anyone with a really old recipe should check with your favorite convenient glaze Calc just to confirm the possible change is significant.

1CA07A92-29C9-4BB6-99A0-C5076420A730.jpeg

Edited by Bill Kielb

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45 minutes ago, Denice said:

I bought some of the Gerstley Borate from a Laguna dealer probably 10 years ago,  my dealer told me it was being dug from a different area of the pit.  He said it wasn't exactly the same chemical composition of the original Gerstley Borate that I was  using.   He said the some of my Gerstley  based formulas may not have the same results.   I don't think this is a big problem in C10 reduction glazes but any chemical change in a oxidation C6 glaze can cause havoc.  Denice

I also found "Gillespie" borate which they claim is identical to Gerstley.  Who knows, right? 

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On 6/12/2019 at 7:56 PM, Mark C. said:

Here's a friend recipe that will maybe work for you its cone 10 soft fired

Here’s our base glaze—could just call it Satin Matt, I guess.  Doesn’t exactly come out to 1000 gram batch, but oh well!

Custer 347

Dolomite 196

Whiting 31

EPK 247

Silica 227

1 percent tin oxide

5 percent zircopax

 

You can paint any colorants over it you like as well

Thank you Mark

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10 hours ago, MFP said:

I also found "Gillespie" borate which they claim is identical to Gerstley.  Who knows, right? 

Gillespe is not. Similar but if they told you virtually the same that  is false. 

Edited by Bill Kielb

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6 hours ago, Bill Kielb said:

Gillespe us not. Similar but if they told you virtually The same that  is false. 

It is virtually identical to Gerstley of a specific year. It was different every few years as they moved through the deposit. Which year they chose to use as their baseline I do not know. I've been using Gillespie for about 15 years, and it's always been stronger than Gerstley during that period, and I've had several customers says the same thing. Typically you'll need 3-4% less Gillespie than Gerstley.

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1 minute ago, MFP said:

I am really starting to get the impression that these "modern" glazes are far more fussy than the one we used in the past.

No, we just understand more about the chemistry involved now.  The minerals were just as fussy back then.  A good example is your Kingman feldspar.  It is no longer available and people have had to come up with a substitute or change their glaze chemistry.  We just know now what changes to make now without guessing too much.  

Back in the past you'd probably just drop any glazes using Kingsman and call it a day.  

The situation with gerstley and gillepsie is the same.  They stopped mining gerstley, but now instead of dropping the glazes that use it, people have an analysis of it's make-up and can recreate something quite similar.  PROGRESS!

But yes, cone 10 glazes are still quite simple, we just know the science and durability better and can be more picky about what we create.

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31 minutes ago, MFP said:

I am really starting to get the impression that these "modern" glazes are far more fussy than the one we used in the past.

Only in that we understand them better, and are more focused than before on making glazes that are durable and safe, rather than glazes that just look good and are easy to make.

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1 hour ago, liambesaw said:

No, we just understand more about the chemistry involved now.  The minerals were just as fussy back then.  A good example is your Kingman feldspar.  It is no longer available and people have had to come up with a substitute or change their glaze chemistry.  We just know now what changes to make now without guessing too much.  

Back in the past you'd probably just drop any glazes using Kingsman and call it a day.  

The situation with gerstley and gillepsie is the same.  They stopped mining gerstley, but now instead of dropping the glazes that use it, people have an analysis of it's make-up and can recreate something quite similar.  PROGRESS!

But yes, cone 10 glazes are still quite simple, we just know the science and durability better and can be more picky about what we create.

Last add:  Cone ten is a thing because the earth melts at cone ten. Cone six is a thing because  ...... nobody seems to know exactly, maybe one of the wars or energy  but to get cone ten stuff to melt at cone six,  boron is an easy to use glass former that helps everything melt.  Under UMF (unity molecular formula, circa 1910) 0.15 Boron gets you cone six, 0.42 Boron gets you cone 04.

Cone 04, no idea why that is a thing either!

Many  cone 6  and 04  glazes are simply cone ten with the proper amount of Boron added. Gerstley is mined, gillespie is produced. Many newer glaze recipes use  Boron  frit instead. Frits  are manufactured materials, not directly mined and generally produce  very consistent results but often less variegation than gerstley.

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Now that is quite illuminating and useful.  It certainly de-mystifies this quite a bit. I thank you!   Since I was a production potter, I still have a considerable volume of my Kingman glazes as well as at least 30-40 pounds of Kingman. It would be nice to know how to adapt them to cone 6 as I am hearing the part about the energy savings. What I am not certain about is how they will perform in an oxidation atmosphere. We did very heavy reduction in those days stating at 010.  Since many are iron based glazes, it is likely they will be duds in oxidation. 

The reason cone 04 is a thing is that it is a temperature that is approved for elementary  teachers to use in the classroom.  If you go to online stores that sell school supplies for teachers.....there are  full of 04 clays, glazes, etc. They also contain some cone 6 stuff for high school teachers.  Elementary teachers have to do 04. Sometimes you can get much better deals than on pottery sites....for example, I needed some pottery plaster to cast drying batts....I got 2 fifty pound bags for what one bag cost me from a pottery supply place with $5 shipping!  There are at least three of these stores on eBay. 

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Elementary teachers tend to do cone 04 work because there has always been an abundance of premixed glazes available for low fire work. Those glazes are easy to use, and have more color options that younger kids like, like bright colors. Until recently, there weren't all that many good cone 6 glazes available. Elementary teachers can do cone 6 or even cone 10 work if they want to, as long as the materials are certified non-toxic and safe for kids to use. Cone 6 and 10 glazes can be certified non-toxic just like 04 glazes.

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I wonder if that is uniform....some of these things are labeled as "not appropriate"...maybe because of composition.  Went out today to try to make friends with this new clay body....making progress.  Do you know anything about that cone 6 porcelain from Georgie's in Portland? They claim it vitrifies at 6. I finally had inspiration today.....but it involves porcelain. 

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7 hours ago, MFP said:

Now that is quite illuminating and useful.  It certainly de-mystifies this quite a bit. I thank you!   Since I was a production potter, I still have a considerable volume of my Kingman glazes as well as at least 30-40 pounds of Kingman. It would be nice to know how to adapt them to cone 6 as I am hearing the part about the energy savings. What I am not certain about is how they will perform in an oxidation atmosphere. We did very heavy reduction in those days stating at 010.  Since many are iron based glazes, it is likely they will be duds in oxidation. 

 

This might help.  If you look at the comparison below Kingsman is similar to G200 (both potassium feldspars). It has nearly the same silica to alumina ratio is slightly higher in sodium, slightly lower in potassium and slightly lower in calcium. I’ll dismiss iron because they are nearly identical and as natural products this likely varies somewhat.

The idea - look up G200 glazes on Glazy, substitute Kingsman and tweak your results if necessary. The other idea is I forward the spreadsheet to you (private message), it is free and now contains kingsman and you can fashion your own glazes. The backstory on the spreadsheet is it was created by Matt Katz (formerly of Alfred university) , it is free on his website (ceramic materials workshop). We added some research and minor programming to it and received his permission to redistribute.  We use it in our basic glaze formulation  videos and it is a bare bones worksheet that depends on stull (1910) which was rediscovered by the pottery community within the last say ten or so years. Stull is pretty easy to learn and indicates trends in glazes plus easy to understand boron addition to move the cone ten glazes down to cone 6.

let me know, I can send you the sheet with Kingsman in it and a link or two to some simple videos

Just an idea though if it helps.

D816AB18-AEA2-4EF6-9D1D-0789B0308B55.png.5c5d2f8cfb1fe0d1f3a53b910f0ee2c4.png

Edited by Bill Kielb

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Another approach would be to use glaze calc software to redo recipes to include the Kingman spar. In the recipe below the combined KNaO matches Mark's recipe. Other oxide levels are the same in both formulas. Like you can see the main differences are a decrease in the amount of Kingman spar needed and an increase in the silica needed with the Dolomite and Whiting amounts tweaked.

Kingman 318

Dolomite 195

Whiting 33

EPK 245

Silica 256

total 1047 (I rounded the numbers off)

(Tin oxide 1% plus Zircopax 5%) 

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