Crystalline Glaze Chemistry

[glazenerd]

Tyler:
My decision to butt out of the room came long before you started posting again. I enjoy the exchanges, makes you think.

Not tough at all actually, now this was tough: having my 85 yr. old mother laying in my kitchen floor giving her CPR, while trying to dial 911... Now that was tough. This exchange was a cake walk. She is home and resting now.

Nerd

 

 

Edit: forgot to answer the question about Molybdenum. I have not fired them in over a year Tyler. I had mediocre results at cone 10, and dismal results at cone 6. I was trying to get them to develop at cone 6 and concluded there was just not enough heat to get the job done. Moly has a melt temp above 4000F, if I recall correctly. Sometime this fall, or early winter I am going to fire some moly again.

[Tyler Miller]

My condolences about your mother. It can be a tremendous weight.

[Dick White]

What I was hoping for was a non-technical educational example that show the decision making process. I realize that there's no cookie cutter firing program, there's nothing hard and fast about ceramics. But it can help to see the decision making process involved in firing and how that informs artistic/studio practice.

 

 

And that is what I offered. You melt your glaze to it's appropriate maximum temperature, drop back to 2000F and then do whatever you want for however long you want as long as you stay above 1800F. Then turn the kiln off and wait until the day after tomorrow to open it.

[Tyler Miller]

Not quite.

 

But that's cool.

 

Here's an old CAD article I like. It gives a sense of practice and expectation I was hoping would enter this discussion.

 

https://ceramicartsnetwork.org/daily/ceramic-glaze-recipes/glaze-chemistry/the-new-world-of-crystalline-glazes-developing-beautiful-crystals-in-reduction/

[Dick White]

Well then read the rest of my previous post, which I will repeat here for your ease of study - "It is my observation that the crystals grow faster and with a more spikey texture in the higher end of the growing range and slower with a softer more flowery texture toward the lower end of the range. One can raise and lower the temperature for intervals within the overall holding period and cause the crystals to take on variations in the texture, including bulls-eye targets caused by repeated up and down tweaks - always staying within the growing window."

 

For a more explicit decision tree: hold for a period of time at the higher end of the range if you wish spikey growth, the exact length of time is of your choosing and exact temperature is of your choosing; and/or cool to a temperature toward the lower end of the range for softer more flowery growth, again for the length of time and temperature of your choice; and/or raise and/or lower the temperature for additional periods of time to create visible "growth rings" as the crystals continue to expand. As for specificity, the upper range of the growth window is anywhere between 1900F up to 2000F, while the lower range is between 1900F down to 1800F, and the hold time interval for any particular segment can be anywhere between 30 minutes and 6 or more hours.

 

For example, a composite of some my firings:

 

R1 - 400/hr to 2000F -- rationale, just get her hot.

 

R2 - 150/hr to 2195F -- I fire to cone 6 and that's what temperature I use. 150F/hr is what my kiln does best in this range.

 

R3 - 250/hr back to 2000F, hold 30 minutes -- bring it back down gently

 

R4a - 250/hr down to 1950, hold for 1-3 hours -- because that's what I decided to do today, want some spikey growth.

or

R4b - 350/hr down to 1850F, hold for 2-4 hours -- because tomorrow is Wednesday, as good a reason as any, flowers are nice on Wednesdays.

 

R5a - 150/hr down to 1825F, hold for 1.5 hours -- because, as my Mother would tease me, to make you ask why, and besides, she likes the flowery ones.

or

R5b - 150/hr back up to 1950F, hold for 1 hour -- for no particular reason but I had to go somewhere up after holding R4b at 1850. 

 

R 6 - 150/hr down to 1750F - the nice lady in seat 4F asked me for a soft landing this time, otherwise I would have just turned it off and crashed.

 

In other words, your artistic practice can be whatever you want as long as your studio practice keeps the ramps and holds for the crystal growing period between 2000F and 1800F. Once you drop out of the window, growth stops and it is unlikely to start again even if you bring the temperature back up, so stay in the window and play.

[Tyler Miller]

I won't say the sarcasm is undeserved, because it probably is, but this is still a little unhelpful. Thank you for including times in your sarcastic decision tree. That was what i was going for. I got X result from doing W, Y, and Z with B recipe. Yes, experimentation is necessary, but a concrete example provides a kind of beacon.

 

Fara Shimbo's book provides a number of firing schedules and examples of what can be achieved with the recipes she provides. Yes, the higher temp creates spikier crystals and lower temps create rounder crystals. But there are other factors to account for, that have been accounted for. Like bringing the glaze down slowly and steadily through the devit window creates variable effects in the crustals, whereas holding creates more regular effects. Time within the window matters, and while it can be whatever you want, obviously a 1 hr hold isn't going to look like a 5 hr hold.

 

People can and do replicate effects, and guidelines toward gaining those effects gives confidence. Like how Diane Creber explains her process with goldstuff and how to get different colours in reduction. And if you look, people shoot for those benchmarks. The results are unpredictable, I realize, but things aren't as plain as you state either.

 

I've held off giving any advice myself because I don't have massive experience with crystalline glazes--I haven't touched an electric kiln in probably 5 years and fire almost exclusively in reduction. Tom was in a position, I think, to speak about the finer points of passing through the devit window.

 

But maybe I've worded it wrong. What I was hoping for was a result and the set of practices that got it there. I don't think just asking for a firing schedule fully expressed that. In which case, the sarcasm I've received is deserved, since the question seems foolish.

 

Thanka for answering.

[Dick White]

The challenge of crystalline glazes is that there are so many, too many, variables that attempts at precision are often met with lukewarm success. Some variables are controllable, other variables are at cross-purposes to one another, and some things just happen. It is joked that the neighbor's daughter sneezing in the night could cause gravity waves in the kiln. As so we have to use our own version of Ockham's Razor - simplify the number of things you are trying to do at once. Especially when starting your journey through this rabbit hole.

 

One thing that you just mentioned will be especially challenging - a gas kiln vs. electric. Because of the volatility of Zn in reduction together with the critical need for the Zn in this process, your gas kiln atmosphere will have to be very precise at all times. There are folks who fire electric kilns with assorted reduction-inducing devices to limit the creation of a reduction atmosphere to only the times it is needed. Some of these devices are crude (mothballs), some are challenging manual practices (alcohol or oil drips), and others are expensive technical additions that are not generally available anymore (the Fallonator). Other folks use a very expensive computer-controlled gas kiln that can be programmed to maintain a specific atmosphere minute by minute throughout the firing. The rest of us use the common digitally-controlled electric kilns and spend our energy worrying about glaze content and application, rather than trying to engineer specific roller coaster rides through our peculiar amusement park's downfiring tunnel.

 

Enjoy the ride.

[Guest JBaymore]

 

 Because of the volatility of Zn in reduction together with the critical need for the Zn in this process, your gas kiln atmosphere will have to be very precise at all times.

 

Yeah....... that.  Excellent reminder for folks, Dick.

 

I once had a BFA student doing a senior technical project working this problem in reduction firing.  And without serious instrumentation and controls..... he learned a few "lessons" in developing consistency.  Unfortunately, a lot more "rule outs" than "rule ins".... but he did a good body of work and research and learned a lot (so did people watching him).

 

Consistency is pretty much the 'holy grail' of this for people who work this stuff.  SO many variables that are tough to fully control given our types of forming methods and nature of equipment.

 

'Back in the day'..... I had a technical consulting client in the Boston area I worked for who was a macro-crystalline potter.  She was working in the era when the cooling controls were a good pyrometer (with platinum thermocouples) and a deft hand as turning electric kiln switches on and off.  She got me involved because of my 'glaze orientation' (teaching it at MassArt) and also my early use of computers in the studio.  We then were involved with one of the first companies that was working on studio level digital kiln control systems... a company (don't know if it still exists) called Digitree.  Took a lot of testing and code work on the hysteresis issue of temperature over and under shoot.  We had it working.... at what today would be considered pretty primitive level.... but then it was kinda' "revolutionary" in how it cut the work load and upped the consistency.

 

The controllers now are SO nice.  And from an NCECA presentation that some of the system manufacturers did a couple of years ago... we can expect some great improvements in their firing effect modeling soon.  How far we have some since about the late 1970's.

 

best,

 

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

 

Edit:  Posting this above caused me to check and see.  Just found Digitry....they still exist: http://www.digitry.com/

[Tyler Miller]

Dick, John

 

Thanks for your replies.

 

I should say I'm not personally going to try to fire crystalline glazes in a gas kiln. I'm just looking at this like a beginner and trying to tease out useful and orienting information a beginner would find useful. Since I found that initially lacking.

 

Out of this, I've got the following: atmosphere control is important. Accurate controllers are essential, and results are unpredictable, with consistency as the desired end state. In addition, there are complex variables at work, not all of which you need to focus on immediately to be successful.

 

How is this grounded in your studio practice? When firing crystalline glazes what do YOU strive for? How do you measure success or failure? You've said that you focus on application and glaze content, because that's most in your control. What is your method there? Are you talking about seeding and colourants or...? Do you post-fire reduce or strike fire? What is the benefit of the latter? It seems a less complex option for altering a result.

 

I'd like to hear more about that.

 

-Tyler

[Dick White]

My sincere recommendation to any crystallier just falling into the rabbit hole: Stay in the middle of the path until you have your bearings. Topics like band gaps and electronegativity and growth structures at 1899F vs 1901F are totally irrelevant at this stage. Getting the feel of what it takes for it to work at all is more than enough to struggle with. When you are able to regularly (i.e., more half the time) obtain an outcome at all with a published middle of the road recipe and a several hour hold anywhere in the middle of the growth window road, then, and only then, start to explore the more obscure recesses of the rabbit hole. The Shimbo and Creber books are good references, as is the Ilsley book. If you want more explicit cookbook data on firing schedules and colorant combinations, I recommend the Price and Price book - many pictures with an explicit key for each.

[Tyler Miller]

Dick,

 

That's a fair answer. Thanks.

[Dick White]

Tyler, welcome to the rabbit hole. As was so accurately described by Alice (In Wonderland), things down here in the rabbit hole are not the same as up there in the real world...

[Tyler Miller]

Dick,

 

I've been down the rabbit hole. If you want to know my experiences, I'll be happy to share. I'm genuinely disappointed no one else is willing to share. Narrative can be a helpful thing. I tried crystalline glazes to early in my ceramics career. First time I fired, it was in hard reduction (didn't quite know what oxidation looked like). The book I got the info from provided a batch recipe and a "firing schedule.". Fire to cone 10, then down to cone 6. Which is useless information. I used this, without knowing about holds and the proper temps. There were other issues as well. I wasn't good at getting smooth surfaces, which doesn't help. Nor did I really know how to apply glaze. I have three successful crystalline pots to my name. One with my mother, one in storage, and one an ex broke. The success? From that laguna premix. Found a friend with a controller and finally got crystals. That's my experience. Colour was awful, so I never bothered again. I might try post fire reduction at some point, but but it's a low priority.

 

I remember once, I got some advice about shino. I cautaued because I thought the guy was an expert. The "secret" advice he gave was just second hand knowledge. Made my face hot as he gave it to me. I felt lied to. He didn't know the method at all. No hands on experience. I still think he thinks he did me some favour that I'm ingrateful for. I had found his trick months before. The "big secret" actually was floating around the internet for years. Ruined the depth of colour. The real method, just a simple thing. And no big secret. Found in a narrative by a prominent potter. No big secret either. If he ever wants to know how to really do it, all he has to do is ask. I've got a few other secrets as well he might like. I don't hold any ill will anymore, maybe one day I'll buy him a beer.

 

That's why I've taken the position I have. Quality information is hard to come by, even from apparently reputable sources. And when you're without a compass, it's discouraging. Doubly discouragin in a closed and decptive environment. Real world experience and sharing real world stories is really helpful. If you ever want to share yours,successes and failures, that would be much appreciated. Talking things out in a dialogue makes things easier. Books are great, but stuff's always left out. And when you don't know what you don't know, you don't get very far.

 

Cheers, Dick, you're a good egg.

[Dick White]

I have to admit, I have never tried any of the commercial crystalline stuff. It used to be just the Laguna dry mix Crystal Palace or something like that. Now you can buy it premixed in pints. Ackkk. Maybe for others, but none of that here. And let me guess on that shino - soda ash is hidden right there in plain view, dissolved in the water in your spray bottle...

 

But seriously, you've merely been a guest in the foyer of the crystalline rabbit hole and you bumped into the closet door trying to hang up your coat, which was not your fault, but rather we have a very strange way of doing our doors and closets down here. So you left to pursue other things. That's ok too. And now you wandered by again and looked in the window. Sure, c'mon in. Once a year I teach an 8-week course in this at one of our local art centers. We can't do that over an internet discussion group, just too much and a lot of the glaze mixing and application is done by feel which we can't really discuss as quantitative measurements. Yes, there are measurements, but you work by feel, and that takes practice.

 

For distance learning (the new buzzword at the college) in the early stages, I return to my recommendation of the Price and Price book. Some would deride that text as paint-by-numbers art compared to the Old Masters Ilsley, Creber, and Shimbo, but it really does lay out the details. Read it twice, and then study the key codes below each picture. Once you begin to make the associations of commonality between the several classes of recipe (e.g., cone 6 vs. 10, which are not precisely 6 or 10, but merely a means of dividing the club into those who fly way up in the stratosphere vs those who fly down in the troposphere...) and see some of the commonalities between firing schedules, then you can start exploring the variations.

 

Then come back and we can talk some more about confusing things or nuances.

[Tyler Miller]

Once a year I teach an 8-week course in this at one of our local art centers. We can't do that over an internet discussion group, just too much and a lot of the glaze mixing and application is done by feel which we can't really discuss as quantitative measurements. Yes, there are measurements, but you work by feel, and that takes practice

The premix is the same as any other batch, they just give the paint by numbers info. The "middle road" complete with disclaimers is on the tin. It was a good starting point and matches up with the book content.

 

I think I understand why you've kept stories of your successes and failures mum. Cattle salesmen don't give away free milk. . I can respect that. It's premium content. That's more than fair.

 

I really just stepped into this to keep the science accurate and steer things toward experience. Maybe I'll take your class one day.

 

Re:Shino--I haven't used soda ash in any shino since my first year of ceramics. Not an American shino guy. This is a littlw more subtle.

[Dick White]

Some (though not me) abide by the two fundamental rules of a master: 1) Don't tell all your secrets.

[Dick White]

But seriously, I do share what I know (which isn't everything) but some things have too many intersecting dimensions to easily share.

[Tyler Miller]

But seriously, I do share what I know (which isn't everything) but some things have too many intersecting dimensions to easily share.

It's ceramics, not surgery. If you ever feel things are too complex to explain. Remember that you're talking about something that is in books, on other forums, on websites. Others, the "old masters," thought differently.

 

Best,

 

Tyler

[Wyndham]

A very interesting read. I have been done this rabbit hole for many years now and find there is more to go than where I've been.

That being said, an early comment on the types of zinc white yellow and metallic. I have been gifted some metallic zinc powder which was used in making battleship gray for the Navy.

How would one go about creating a glaze test using this material, if at all.

I use a 50% 3110 26% calcined zno 23% sil and a pinch of epk. peak temp 2300f w/5min hold

Looking forward to trying something new just rewired my kiln

Thanks Wyndham

[Tyler Miller]

Calcine in bisque firing in a BIG pot. It grows in volume exponentially and may do goofy things like form streamers. Store air tight or you'll have to recalcine; it's hygroscopic. Edit: this makes french process zinc oxide.

 

Edit for diaclaimer (not so much for Wyndham, for whom this is likely obvious): good ventilation and oxidation is a must. Zinc fumes are a bad news. Ask me how I know

[glazenerd]

Wyndham:

 

Pure metallic zinc ( blue/grey) zincite has a melt temp of around 800F, and a boiling temp around 1800F: it's primary use is a low fire flux and or opacifiers. I bought a 50lb bucket several years back, mainly because someone had ordered by mistake and basically sold it to me for cheap.

I had been experimenting with cone 4-5 crystalline firings: to date my peak temp being 2175F. The draw backs and cautions would be: it does not blend colorants well, like you typically see in multi- colorants standard crystalline recipes It certainly favors copper above all other oxides, and will produce a deeper green even in the presence of other oxides. It is highly reactive to alkali, and will easily vaporize if higher % of alkali are used. It will vaporize in a typical cone six schedule.

 

CAUTION: metallic zinc is highly reactive to alkali and acids, and will cause explosions, high temperature ignitions (similar to white phosphorous) and has the potential to explode in your kiln if improperly mixed with alkalis, or Lewis acids: metallic zinc is a very strong amphoritic oxide. It is used in solid boaster rocket fuel because of it's ignition potential.

 

I would highly recommend you do not calcine metallic zinc because it will simply ignite and fuse to the container. You will have a nice bowl of molten lava looking rocks: ask me how I know.

 

Nerd

 

Edit: Tyler said: "Calcine in bisque firing in a BIG pot. It grows in volume exponentially and may do goofy things like form streamers. Store air tight or you'll have to recalcine; "

 

Tyler, this a seriously bad idea and dangerous for potters to attempt. Explosions and possible spontaneous ignitions can and probably will occur.

 

edit added to caution readers about the potential hazards of metallic zinc.

[Tyler Miller]

Glazenerd, of course it ignites. That's the point.

 

Actually, I'm going to side with you on this. I've done it, it didn't produce the mess you had in your experience. But it's a a bad idea. The fumes are scary. And zinc oxide is cheaper than zinc. And the reaction needs fumes.

 

Use the powdered zinc to cast with. Make some metal soldiers or something. As long as you can control your temps that's safe.

 

Tom, you're right.

[glazenerd]

Ty Tyler:

 

I have not fully explored the different metallic zinc varieties: but to my knowledge there are different levels of purity. What happened in your scenario and in mine are both explained by purity levels of metallic zinc. In my case, after doing some research the metallic zinc I acquired is pure metallic zinc "dust." Not exactly sure how the fineness of mesh plays into all of this, but apparently it does play some role in reaction rates. One of the unfortunate problems in the pottery field: purity level and material grading is usually not addressed.

 

Nerd

[glazenerd]

Post # 6 has been updated with firing information.

[Wyndham]

Thanks for the info. I can see things going very bad very quickly.