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First glaze recipe attempt - looking for flaws and cone


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So I've thrown myself down the 'make your own glaze' rabbit hole. I've spent some time on Glazy (and books and YT) and one thing I don't see is what cone the recipe you have created should be fired at. Is there a why of deducing that from the ratios or from another statistic? I was attempting to make a cheap almost satin white glaze for mugs and have noticed on the graph that shows other glazes that some with a similar makeup are listed as cone 10 glazes and some are 6, and a couple in between (I'm shooting for cone 6). Is there a way of looking at a glaze on paper and saying that will most likely be a cone 6 glaze (other that actually firing it)?

The other part is I am attempting to make a simple glaze with some of the cheaper materials in my area, is there any glaring mistakes or omissions from this glaze recipe that would need to be addressed before even attempting to fire? https://glazy.org/recipes/65665

25 Custer Feldspar
25 EPK
25 Nepheline Syenite
25 Wollastonite
------
10 Zircopax

 

Thanks for any input!

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Yes, there are categories of ingredients that are fluxes, these will bring the melting point down.  There are a few very strong ones like boron (gerstley borate, boron frits[3134, 3124, et al]) and lithium, and there are others like sodium, calcium and potassium that aren't as strong.

So nepheline syenite is a sodium feldspar-type material, and at 25% would probably lower this glaze down under cone 10, but maybe not quite 6.  The 10 zircopax will probably be problematic too if you're aiming for cone 6, because it is highly refractory and doesn't incorporate into the melt.

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1 hour ago, milksnake12 said:

So I've thrown myself down the 'make your own glaze' rabbit hole. I've spent some time on Glazy (and books and YT) and one thing I don't see is what cone the recipe you have created should be fired at. Is there a why of deducing that from the ratios or from another statistic? I was attempting to make a cheap almost satin white glaze for mugs and have noticed on the graph that shows other glazes that some with a similar makeup are listed as cone 10 glazes and some are 6, and a couple in between (I'm shooting for cone 6). Is there a way of looking at a glaze on paper and saying that will most likely be a cone 6 glaze (other that actually firing it)?

The other part is I am attempting to make a simple glaze with some of the cheaper materials in my area, is there any glaring mistakes or omissions from this glaze recipe that would need to be addressed before even attempting to fire? https://glazy.org/recipes/65665

25 Custer Feldspar
25 EPK
25 Nepheline Syenite
25 Wollastonite
------
10 Zircopax

 

Thanks for any input!

The easiest cone six relatively predictable melt that I am aware of are those that use boron. So basically all glazes are made from earthen geologic products and in essence the earth is cone ten. Cone six is a thing because .............. I don't know, I have never seen a definitive reason for it, but it’s here so in essence one of the easy ways to get down to cone six is to take a cone ten glaze and add about 0.15 boron under UMF.

There are other ways to get things to melt sooner using fluxes (research Bristol glazes) however there are some known decent flux ratios if you will, so simply adding more flux to make things melt sooner often does not result in a durable glaze composition. All this results in various glaze theory based on limits, Stull, etc.... usually relying on the UMF (Unity Molecular Formula) or an extended version of it.

You could enter your glaze in the Glazy calculator and get your results in UMF and Stull. From there you could compare with similar glazes. Glazes melt by composition so generally they need to be fired progressively to have a good sense of their operating range.

Matt Katz has a nice course that is Stull and composition based. You can find it at his ceramic materials workshop website. There are many other decent though and it may seem like a rabbit hole but we are still learning about glaze compositions daily. So lots of room for experimenters.

If it makes you feel any better, I  have a hard time buying any glaze now and prefer to develop my own as I know what’s in them and develop them to look the way I like while being reasonably sure they are durable.

If you enter your glaze in the glazy calculator, what do you see?

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Screen shot below of the UMF (unity molecular formula) of your glaze taken from your glazy link. 

I've added some coloured arrows to try and help explain things. I don't know what you know so apologies if I've over simplified things, I'm just trying to give a general idea of what to look at while looking at a UMF. Very first thing I would look at when trying to determine the range the glaze will melt at would be the silica, alumina and boron levels. Fluxes always equal 1 with UMF, so look at the other things first.

Having a look at the UMF below you can see the blue arrow is pointing at silica @ 3.18  (plus a bit from the zircopax which is zirconium plus silica) alumina (pink arrow) is 0.61  and  0 boron.

Now comes the bit where you look at this and either compare those silica/alumina/boron levels with a glaze with similar qualities or at traditional "limits". There are differing opinions on limits, many interesting glazes fall outside these "limits" but use them as a guideline. For a durable cone 6 glaze alumina falls in approx the 0.25- 0.35 (Roy and Hesselberth) range and ^10 range approx 0.45 - 0.65 (Green and Cooper).  Now have at look at your alumina, 0.61  so this tells us a couple things, either this glaze won't melt well at cone 6 or it's going to be an alumina matte. (more on this in a bit)

Silica in your glaze is 3.18, range for a durable cone 6 glaze is approx between 2.4 - 4.0 (Roy and Hesselberth) your 3.18 should be fine at cone 6, if the glaze melts well you want to get as much silica and alumina into it as you can for durability. ^10 range for silica 3.5 - 6.4 (Green and Cooper)

Boron is 0 in your glaze. At cone 6 most glazes have boron to help the melt. ^6 range 0 - 0.3 (Roy and Hesselberth) for ^10 boron isn't necessary but can be used 0 - 0.255 (Green and Cooper). Bristol glazes use zinc as a flux but there isn't any of that in this glaze either so chances are it's not going to melt well.

Red arrow is pointing to the fluxes in this glaze, sodium potassium and a fair bit of calcium. So back to the types of matte glazes, to get a matte glaze you can have high amounts of the fluxes calcium or magnesium or strontium or barium (not recommended) and to a lesser extent titanium and zinc. You can also have high alumina mattes but these tend to cutlery mark so not the best for functional surfaces. Green arrow is pointing at the silica:alumina ratio. At the 5.24 you can look at this and know it would be a high alumina matte plus have matting qualities from the high calcium level. (if the glaze melted at cone 6 which I don't think it will)

Play around with the chemistry on Glazy,  get some boron in there, drop the alumina to a lower level, I'ld also raise the silica:alumina ratio up a little bit if you don't want cutlery marking. 

Welcome to the land of rabbit holes.

UMF.png.bb0b7e50d14f976fd1328b36357663bc.png

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Thank you so much for taking the time to explain that! That helped a lot! 

I was watching John Britt's videos and he mentioned the satin range is normally around a 5:1 SiO2 to Al2O3 ratio.  I was attempting to get a somewhat satin/light mat surface, so I kept bumping up the CaO to try and get it there. 

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Hi MS,

Best wishes for good glaze outcomes!

Clear and liner glazes seems like a good place to start, aye; finding what fits your clays, that's the rub in my (limited) experience.

Your recipe reminds me of Tony Hansen's 5x20, found here https://digitalfire.com/4sight/recipes/original_cone_6_base_glossy_glaze_37.html; from there, you may find other useful articles, recipes, etc. on Mr. Hansen's site. Another good source (imo), Hesselberth's FrogPondPottery site, see midfire glazes, particularly the notes/comments http://www.frogpondpottery.com/tested-glazes/mid-fire-stonewareporcelain/ ...and Mr. Hesselberth's (and Roy's) book, as well. Each clearly indicates the target cone. I'm having good results with Bethany Krull's "Wollastonite Clear" on the red, black, and buff clays I'm using. Many recipes "out there" - some are from reliable sources and include helpful notes as well. 

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3 hours ago, milksnake12 said:

I was watching John Britt's videos and he mentioned the satin range is normally around a 5:1 SiO2 to Al2O3 ratio.

Yes but there is more than one mechanism at play. Your glaze has a lot of calcium, combine that with a slow cooling and the high alumina and it could be too matte. Might be okay but might need to bump that ratio up a bit. BTW glazes are relatively inexpensive to mix up, I wouldn't get to hung up on making a glaze with "cheaper materials".

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