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Macro-Crystalline Zinc Glaze - Combining With A Clear All-Over Glaze?


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Guest JBaymore

Tom's hit on a variable most don't think about--thermal mass. Underwhelming crystals from a regular cooling cycle would benefit from a large, fully packed. extra insulated kiln. There's still a devit window at work, and crystal growth still a function of time within that window.


In the "woodfire community" often get nice larger-than-micro-smaller-than-macro crystals in the large wood kilns due to the typical very large thermal mass and very slow cooling.


Gave me an idea.... try some form of macro-crystalline formula in the noborigama or the anagama.  Problem is with the long firing up-cycle... many "standard" glazes with alumina in them r un a lot.... so maybe ALL of the glaze would run off the piece.  Need a BIG catch basin  :P .





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Nerd said up above a few spots...


... As Oly pointed out: 62.00 +/- molar silica is proportionate to a 20% silica addition. My Nerd O' meter thinks if you used this recipe as a base for a thicker growing medium at optimal flow: and added 10% silica and incorporated the usual holds: you very well may end up with mega crystals.. Hmmm... crystalline experiment # 2489.



Interesting line of thought there. I bought this book for other reasons, and it's a pretty good general reference book for those other reasons. But I passed by that chapter because 1) I was already deep in the crystalline rabbit hole, and 2) those 2 recipes just didn't square with what I understood at the time - 75% frit/25% Zn and no silica? and the other one with no Li? But now that you mention it... One of the things I have done in my perambulations about in the rabbit hole is collect recipes wherever I find them and then plunk them into GlazeMaster as a convenient recipe filebox. And it magically calculates the UMF, which I then tabbed into a monster spreadsheet (you know, recovering accountant and all that, sometimes I fall off the wagon and do silly things like make a spreadsheet...) which I then ran some statistical analyses on (and sometimes when I fall of the wagon, it runs me over...) to see if there was any pattern, e.g., the standard argument of glaze "limits" but only for this peculiar brand of idiocy. And yes, there does appear to be a pattern of limits. So... when I set this 75/25 glaze beside the usual limits, it fits in as if it is one of the family. The increased Na flux from the overload of 3110 probably offsets the need for Li, and the overload of 3110 brings with it almost enough silica to cover the need. And when that ricocheted off the back of my brain, I tried subbing 413 in the calculation - and that one isn't too far off either. And then just for S&G I threw in my other 2 standard crystalline frits - 644 and 493 - but no love there. Neither of those have enough Si on their own. As if I didn't have anything better to do than experiment some more...

Edited by Dick White
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Your explanations of frit varieties and chemistry gave an excellent reference as to why frit 3110 is the popular choice in crystalline recipes. Being a fellow Glazemaster software fan, I would encourage you to use the "formula limits" setting to write your own, using the values from your spreadsheet. 62.00 molar seems to be the median value of choice among the recipes I have collected and written. Just as 35/1 Si/AL ratio seems to be the median value....and potters wonder why it crazes so much.


Funny story: when I met with Ron Roy at NCECA 2016 in KC, we were talking material costs and chemical analysis. We were talking about specific clay recipe additions and he was trying to recall costs. I was carrying my laptop (which crashed recently) and I pulled up my spreadsheets of material costs, chemical analysis, and my inventory: and said.. no problem have it right here.  He gave me one of those- you are a strange man looks.... to which I told him later: I am a Nerd, what did you expect?


Half the battle of crystalline growth is the fluidity and thickness of available glaze: so I do think this recipe could be manipulated to grow rather large crystals. The battle is going to be flux levels: this much frit will run like a river if it is over-fluxed. The next battle would be dialing in the right peak temp; to catch it at its optimal flow, before it flows into a catcher.



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Nerd, that's exactly how I do it, keeping things within the limits I developed in the spreadsheet. One minor difference from your observations - I'm trying very hard to stay on the "cone 6" party bus while the real partying is going on in the "cone 10" bus. In my spreadsheet, I separate statistics of the 6 and 10 recipes, and the unity limits for Zn are lower for the sixers, running between .5 and .6, because of the Li typically added to the cone 6 recipes intrudes into the flux unity.


And as an aside, you have mentioned your beloved but crashed laptop. Do you still physically have it? Was it a mechanical failure of the disk or something else made it unusable? Have you tried disassembling it to extract the bare drive and re-mount it in one of those cheap external hard disk cases? The machine is dead meat now, so nothing to lose by taking it apart, but you may find the raw disk can still be addressed and then retrieve the lost data.




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Cone 6

This is a cone six firing, with only two hours worth of hold (need to check my firing sheets).

crystal 01

This is a cone six crystal.
There are some chemistry secrets: and I accept Visa, check, cash, or Paypal...  :o
Actually I will be adding to my Crystalline Glaze Chemistry over a period of time, and will give away all of my secrets.. Well, all except two maybe,,,


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  • 2 years later...


On 5/3/2020 at 2:56 PM, pkenin@comcast.net said:

IN the middle of 100 glaze crystalline tests. No problem with shades of green, shades of blue. Looking for tips on two things. 

#1 Oxidized red ground or crystals without the use of cadmium ( toxicity) Red is developed in reduction. Typically, 3-4% copper colorant is fired in oxidation (green) and then reduced during the cooling ramp by heavy reduction at 1350-1650F range. There are some who "strike" fire: reheating the piece to 1350-1650 in a reduction atmosphere. You can also grow crystals on a red bodied porcelain. 

#2 Yellows  straw yellow is made with low % of red iron ox (0.75 to 1%) There are rare earth lanthanides that will produce a medium yellow at cone 10- but pricey and a bit hard to control.

#3 Creation of distinction of ground colors and crystal colors  Zinc is used to control population. (Field to crystal ratio)  The base crystalline recipe is: 50% frit 3110, 25% zinc, and 25% silica. The 25% zinc is adjusted up or down: increasing produces more crystals, and decreasing creates more open field. Run a test at 24% and see how the results appeal to you. ( artistic preference decides population) if 24% is still a touch heavy, reduce to 23.75%, or raise to 24.24% for slightly more. Many zinc varieties out there; some more reactive than others. Which is why you see such a wide variance in recipes: 23.25 up to 30% zinc. 


Thanks all   Perry Kenin 

More info in the link below. On the first page-4th post zinc additions are discussed. There is a pic that shows 24-25-26% zinc additions.


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