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Eutectics Calculator


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 There was a recent thread where glaze eutectics was brought up. Stemming from that was a link to an article by Robert Magnuson in the Feb 2018 Ceramics Monthly which contained a link to a eutectic calculator, "EuCal",  he created. Magnuson discusses an interesting aspect of eutectics, to quote from the article:

"One of the most interesting aspects of eutectics isn’t how they melt, but how they solidify. When a eutectic mixture cools from the molten state, the individual components all stay molten together until they solidify. When they do, a transparent glass is formed. If the molten glaze contains ingredients that are not part of a eutectic, these ingredients may solidify separately while the glass is still liquid, leaving tiny crystals suspended in the glass, producing opacity and other effects in the final glaze. But, if a glaze contains only eutectic mixtures, a transparent glaze will result.

Very few glazes are based around a single eutectic and most incorporate both alkali (R2O) and alkaline earth (RO) oxides. Any combination of the eutectics of Na2O, K2O, and CaO (see left) will result in a transparent glaze. For such a neat trick, it’s surprising you don’t hear about it more often. If you have ever tried to formulate a fully transparent glaze by trial and error, you know it isn’t easy to do—unless you know this trick."

Since the time of that publication Magnuson has updated and revised his EuCal. Version 1.8 added borate eutectics for the alkali fluxes and the latest version, 1.9, added a calcium borate eutectic. This could be very useful as it now brings mid and low range glazes into play with the calculator. There are some provisions, see the read me file linked below.

Given that not everyone has access to the links in the article Jennifer Harnetty asked Magnuson for permission to link the read me file plus the eutectics calculator here to which he very kindly agreed to. I've added the links to the updated version below.

I realize this isn't an area that gets a lot of discussion but perhaps as time goes by as more people get familiar with the calculator it can be utilized as a stand alone piece of software or perhaps in tandem with Stull charts. Lots of food for thought here.

Link to the Feb 2018 article here:  https://ceramicartsnetwork.org/ceramics-monthly/ceramic-glaze-recipes/glaze-chemistry/techno-file-using-eutectics/

Link to the User File here: https://ceramicartsnetwork.org/wp-content/uploads/2018/01/EuCal_1_9_User_Guide.pdf

Link to the EuCal here: https://ceramicartsnetwork.org/wp-content/uploads/2018/01/EuCal_ver1_9.xls

 

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  • Min pinned this topic
1 hour ago, Min said:

"One of the most interesting aspects of eutectics isn’t how they melt, but how they solidify. When a eutectic mixture cools from the molten state, the individual components all stay molten together until they solidify. When they do, a transparent glass is formed. If the molten glaze contains ingredients that are not part of a eutectic, these ingredients may solidify separately while the glass is still liquid, leaving tiny crystals suspended in the glass, producing opacity and other effects in the final glaze. But, if a glaze contains only eutectic mixtures, a transparent glaze will result.

Great stuff! I always forget sort of a practical potters trick to clarity so I need to make sure to mention it here. A bit less scientific, but a nice practical potters approach, I think to clarity.

Anyway done by Sue McCleod and offered free to anyone who is interested in eeking out their best clarity. https://suemcleodceramics.com/getting-clarity-with-clear-glazes/

 

Edited by Bill Kielb
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Hi Bill,

Okay, so I'm just poking around with the EuCalc, I'm using a Mac. I took Sue McLeod's clear from Glazy and plunked it into the calc. Don't know if one would get the same results using Excel? Looks like there is excess alumina and silica that isn't taken into the melt but I could be reading this wrong. I'm heading out early tomorrow a.m. to go wilderness camping, won't have a chance to play with this some more until I get back Sunday night.

289329454_ScreenShot2021-05-12at4_54_45PM.png.73bef28ccddda2572802d93562e11dcb.png

 

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9 minutes ago, Min said:

I took Sue McLeod's clear from Glazy and plunked it into the calc

I don’t think her studio clear is the clearest it can be likely for fit reasons, so it will be interesting, but I did think her tests were a nice thing to know and doable for most potters so a practical observation. I really like her, she freely makes her tests available and shares.

 You may have something pretty cool with the calculator though, so that would be handy as well for serious glazemasters.

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Hello everyone.  I'm the guy who put together EuCal.  This Forum is new to me, so I have some catching up to do, but I'll do my best to help out where I can.  No calculator can predict everything.  Testing is always still needed.  When using EuCal, you will find that most glazes will tolerate SOME excess SiO2 and Al2O3 before they start getting opaque.  The recipe posted recently could probably be made slightly more transparent by reducing the EPK and Silica a little bit.

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13 minutes ago, BobMagnuson said:

Hello everyone.  I'm the guy who put together EuCal. 

Nice work, interesting tool. Hats off for providing it. If you look a post or two above there is a trial and error method, sort of a potter friendly way to sneak up on clarity. The young lady that wrote the article freely shares her test findings as well, so your calculator and distribution sparked my memory to share her -  test, test, test  style solution. Some potters love to calculate, others love to test. Your calculator seems very intriguing IMO.

The recipe posted above is not intended to be one of greatest clarity, in fact there is evidence in the recipe  that her design intent addressed other issues for her studio clays. Interestingly though, her method does involve finding the best amounts of silica and alumina for,greatest clarity by trial end error if you will.

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14 hours ago, Bill Kielb said:

 Some potters love to calculate, others love to test.

I'm inclined to do both.   And I agree with Bill Kielb on thanking you Bob Magnuson.

Edited by blackthorn
so much for hash tagging names
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On 5/13/2021 at 5:39 AM, Dick White said:

this glaze chem stuff IS wilderness camping

Or....it could be viewed as another map, to help get out of the chem wilderness. :)

Adding my voice to say thank you to @BobMagnuson for both sharing his calculator plus making himself available here for questions and comments.

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@BobMagnuson, wondering about zinc eutectic and reduction. If the temperature for zinc oxides eutectic point is 1030C / 1886F (using 0.54 CaO + 0.46 ZnO + 0.13 Al2O3 + 1.39 SiO2) have you found a difference between oxidation and reduction eutectics for zinc given zinc will start to volatilize in reduction around 900C?

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You are correct in that, under reducing condition, zinc oxide converts to zinc metal and will volatilize around 900C.  This could cause glaze immaturity due to loss of flux, or bubbles and pinholes.  If reduction is started later in the fire - after the glaze has melted, there may be some protection from the volatilization, but I don't know that for sure.  Does anyone out there have a successful reduction glaze recipe that includes zinc?

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Had a thought about something when posting the recipe above in regards to the whiting. Looking at the eutectic chart, if we know the temperature for the boron calcium melt is 990C/1814F and we know the LOI for whiting is roughly 45% then using sideways logic it would make sense to go slow and possibly do a hold around 990C/1814F to clear the bubbles in boron glazes containing a significant amount of whiting. Does that seem logical?

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46 minutes ago, BobMagnuson said:

Does anyone out there have a successful reduction glaze recipe that includes zinc?


Yes.  the college studio standard clear (and the base glaze for ~ four other glazes) cone 10 reduction glaze has 2-5% zinc and there is no evidence that the zinc evaporates.   my memory says that some reduction crystalline glazes also have lots of zinc but i don't have the recipes. 

question:  Has anyone set down and calculated zinc oxide decomposition to zinc vapor in a combustion kiln environment for the various oxygen levels at various kiln temperatures that the glaze mixture will see?  All the data should be available in the CRC handbook or the NIST database. 
LT

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So there are indeed reduction glazes that start off with ZnO in the recipe.  But Robins Clear looks like it would work fine at cone 10 without the zinc, so if some is lost due to reduction firing it would be hard to tell. Now, if there are reduction fire zinc crystal glazes, that's a different story. If zinc crystal glazes can survive reduction fire, then zinc loss due to volatilization probably isn't very important.

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43 minutes ago, BobMagnuson said:

Now, if there are reduction fire zinc crystal glazes, that's a different story. If zinc crystal glazes can survive reduction fire, then zinc loss due to volatilization probably isn't very important.

Crystalline glaze potter, Dianne Creber has some pots done with reduction but the reduction is done after the pots have been fired in oxidation to cone 10. She does either a refire to a lower temperature or starts reduction on the way down from an oxidation firing. From the upper end of 1900F down to 1250F reduction to change the colouring oxides. I remember doing button tests of all the glaze chemicals, there was nothing left of the zinc oxide when fired in reduction to cone 10.

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The evidence suggests that while ZnO is easily reduced to Zn and volatilized under reduction, once it enters the melt the loss doesn't happen, or is at least minimized.  I think ZnO can enter the melt either by forming an alumino-silicate eutectic with calcium or simply by dissolving in the liquid glass.  Some zinc crystal glazes have little or no calcium or alumina.   In that case, EuCal isn't helpful, because the simple binary R2O:SiO2 eutectics are not included in the calculations.  If calcium and alumina are present, zinc needs to be "excess to the eutectics" in order to leave enough available to form zinc silicate crystals as the melt cools.

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Having dabbled in crystalline glazes more than a few times, my understanding of the process is there is way way way too much zinc (25%+/-) in the recipe for a "normal" glaze, but it is all incorporated into the melt at peak temperature in what might be similar to a supersaturated solution. There is very little calcium or alumina so that the molten glaze is nice and loose (runs like the dickens) for the crystals to grow without any impediments. While the silica molar level is low in absolute terms, with almost no alumina, the Si:Al ratio is over the moon. As it slowly cools, the zinc molecules precipitate out and readily find the excess silica molecules to form and grow the big zinc orthosilicate crystals during the multi-hour hold at temperature. I will try to put in a picture from EU-Cal of one of my recipes. The excess silica is 7.55 and excess zinc is 3.44. That stuff has to go somewhere, so it forms crystals. The crystals also absorb colorants that are in the recipe, but in a standard order of electron valence, leaving some of them in the background. I have not tried a reduction firing, but those crystalliers who have report it's a hot mess if reduced on the way up, but if there are reduceable colorants in play, they will do all sorts of pretty things on the way down after the crystals have formed. (@BobMagnusonAwesome tool, btw. I will be sending you a request message later.)

EuCal_ver1_9dw.pdf

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  • 4 months later...

I'm trying to find cobalt in the materials list and analysis page but all I see is CO2 which, if I'm not missing something, should be a gas.

It's always possible I'm being a bit dense somehow but I'm unable to see my way through this.

Thanks for the software btw. It's helping move a couple of stalled projects.

cheers

*looks like I am using an old version - now the trouble is the v. 1.9 link for download is opening in read only mode

Screenshot (63).png

Edited by C.Banks
further investigation required
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I do have an update to EuCal 1.9.   Dick White was kind enough to update the % Analysis tab.  Lots of the data in mine is quite old - because lots of my ingredients are quite old!  Anyway, I have version 1.91.  If it's Okay with Dick and Min, I'll be happy to share it.  It's also fully unlocked.

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27 minutes ago, BobMagnuson said:

I do have an update to EuCal 1.9.   Dick White was kind enough to update the % Analysis tab.  Lots of the data in mine is quite old - because lots of my ingredients are quite old!  Anyway, I have version 1.91.  If it's Okay with Dick and Min, I'll be happy to share it.  It's also fully unlocked.

yes please

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1 hour ago, BobMagnuson said:

I do have an update to EuCal 1.9.   Dick White was kind enough to update the % Analysis tab.  Lots of the data in mine is quite old - because lots of my ingredients are quite old!  Anyway, I have version 1.91.  If it's Okay with Dick and Min, I'll be happy to share it.  It's also fully unlocked.

If @Dick White is okay with this then absolutely yes. Thank you.

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3 hours ago, BobMagnuson said:

I do have an update to EuCal 1.9.   Dick White was kind enough to update the % Analysis tab.  Lots of the data in mine is quite old - because lots of my ingredients are quite old!  Anyway, I have version 1.91.  If it's Okay with Dick and Min, I'll be happy to share it.  It's also fully unlocked.

Fine with me too. It's an interesting additional level of glaze chem. Thanks Bob for originating it.

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I'll ask admin if they can replace the clickable link in the first post in this thread to the 1.91 updated version. 

20 hours ago, BobMagnuson said:

It would be interesting to hear what other folks are using to open EuCal.

I'm using a Mac and it comes up fine with Numbers.

edit: admin is tied up until the beginning of October. If anyone needs this before then send me a pm and I'll email it to you.

 

Edited by Min
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