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Dawn

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Can anyone provide some basic information about crystalline glazes?  Three main questions have been on my mind:

 

1.  Are these cone 10 glazes?  (Is there such a thing as cone 6 crystal glazes?)
 
2.  I know the most important phase for crystals is the soak.  What temperature is the soak and how long do we soak?  (Length of soak will affect firing costs.)

3.  Any other points in the firing where temperature is critical?

 

Thanks for any thoughts.

 

- Dawn
 


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Erik

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Reply with quote  #2 
I started playing with crystal glazes with my friend Chuck last November, and while we're not experts yet, we have had some success.

There are lowfire crystal glazes, but we haven't messed with them. One book I have has several recipies for the cone 5-6 crystal glazes, but I think on the whole I've liked the pictures of the cone 9-10 ones better.

The soak temperatures we've played with range around 200 degrees at about the 2000 degree level. Most of the glazes we played with have their own sweet spot temperature. We have a transparent blue glaze that only grows a couple tiny crystals at the temperature where a different glaze really takes off, but 75 degrees higher the blue does terrific and the crystals in the other glaze are dull and flat.

I think the optimum time we have been soaking is around the 4-5 hour range. Crystals grow faster at the higher temperatures but the temperature also affects the shape of the crystal. Typically higher temperatures make spiky crystals where lower ones produce round crystals. Of course adding a colorant to the glaze is going to change the growth temperature, as well as the shape of the crystals, in addition to the color. And it will vary from colorant to colorant in the same glaze. We haven't played with it yet, but soaking at two ranges in the growth stage can give some really nice variation to the crystals.

The crystals begin to form in the glaze on the way up to temperature, then melt down as the glaze hits the peak temperature, then regrow as it passes the growth temperature as it cools. It's important to try to hit the cone 10 as fast as possible to keep more of the glaze on the pot. If the kilns struggle to reach 10 over a long period of time the glaze runoff is going to be severe. We tried one firing with a 15 minute soak at the peak temperature because it was recommended in one of my books, and noticed a huge difference in the amount of glaze that ran off the pot, so we cut that soak out and got better results the next firing.

The two books I have that I think were most informative and would recommend are

I can try to answer questions if anyone has some, but I'm still kind of at the beginning end of the learning curve for these glazes.

Erik

dragon

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Reply with quote  #3 
Erik,

I am just starting my crystalline education and I had great success the first firing and now that I tried to make my own glazes I have one big load of glossy light brown vases with crators in them. 
The first load I used the premixed crytalline glaze and just painted it on.
This last load I measured and mixed and added the water and all that and my partner painted his hand thrown pieces since this was going to be his load of crytalline pieces.  They looked ugly to me all beige and the water just soaked right into the bisque....we let then dry for 2 days out in the garage and it was reallly hot out there.  Applied them to the bases and let them dry one more day...then fired them to the receipe in the book....they are now shiny ugly brown things.  A few of the pieces have a blue cast on some the flat areas but mostly that ugly brown...
It looks like the glaze bubbled it didn't run a lot but on some of the bigger pieces it did...but they for the most part 80% just popped right off the bases with not much effort at all...
I wish I had a picture to attach but didn't think of that until just now...will repost with pictures later
going to try again on just test pieces from now on and not use the good stuff util we have a better understanding of this crystal stuff

Artdragons,

John and Jim


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Erik

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Reply with quote  #4 
Was the second glaze you used the same formula as the first? We've found that even slight differences in glaze formulas require full re-testing of the glaze at different temperatures. We also found that the firing schedules for glazes we found  listed in books were a good place to start, but that they required some tweaking. We've also experienced that the same batch of glaze applied the same way and fired at the same schedule in the same kiln can turn out (horribly) different from one firing to the next.

We went through the same thing, we tested our first batch on some inferior test pieces and got beautiful results. The second batch we went all out and made good stuff and got disappointing results. The best thing I can recommend is to keep a good log of every little thing (even so far as the weather conditions and the time you started the firing) and only changing one variable at a time when you're experementing.

Brown and ugly sounds like iron to me, but there's a lot of things it could be. I think we only had one glaze that came out well that included iron (even iron in a gray clay body like HB turns the best glazes ugly browns)

I'd like to see a picture if you can come up with one, and if I can, I'll try to answer more of your questions.

erik



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Reply with quote  #5 
Hey Eric,

No the first batch was a pre mix by laguna that turned out pretty good except for me opening it to early and cracking two of the pieces on in my hand when I picked it up.  It went ping and the rim of the plate just popped right off in my hand.  We used the excuse that it was too thin to start with...less than a 1/8 of a inch in some places even thinner.
But I still opened the kiln to early...this time I let it cool for 2 days after it clicked off.  Just to make sure...boy was that hard.
Will post pictures that Jim took this evening when I get back from Ceramics meeting tonight. 
Thanks Eric!


John and Jim
Artdragons



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Erik

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Reply with quote  #6 
We've had some problems with breaking pots but it even seems to happen long after they're cool. I found that slightly thicker pots stand up much better to removing them from the catch basins (and thicker ones have seemed to build better crystals).  But even thicker pots will crack right at the glaze level on the inside of the pot if you get too much glaze inside that runs to the bottom of the piece. I think that just the stress of the extra glass pulling (or pushing?) can cause fracture lines.
dragon

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Reply with quote  #7 
Eric,

Sorry for the delay in answering your response.  Been pouring lots of pieces to test on.  Eggs and even a longhorn bull, I want to try different shapes other than just cups, vases and platters.

The things I just poured are cone 6 and I was gonna try some of the glazes from Creative Creek and see if I can get his results. 
The high fire cone 10 glazes are what I am working up too.  I love the cobalt and the white crystals!

Well I must admit that the second load of test pieces I did not measure on a scale, I used the method of one table spoon was a gram and worked back from there.  Well that does NOT work!!!!!! Just wanted you to know that I really screwed that batch up. 

I have also been talking with Ginny Conrow and she is wonderful.

I have attached the photo of the supect pieces that shows what happens if you do not use a scale to measure your chemicals. 

John

Attached Images
Name: June_07_Firing_Results.JPG, Views: 5994, Size: 19.10 KB



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tonyreynolds

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I have just found your website through a Google Alerts I have set up on Crystalline glazes and have read the few posts on the subject available here. I hope you won't mind some input from Arizona. I found the base glaze formula in the Diane Creber book to be the best of many I have tried. I fire at cone 6-7-8 and so I tweaked the formula by adding 12% more frit 3110. What I have found is that the firing schedule and the kiln load are as important if not more than the chemistry. Rapid climb to temperature (2240f), rapid drop to the growing temp (yes, I open the kiln (L&L Jupiter) to drop the temp to 1910f and then a good soak of at least 4 hours. Some samples of work can be seen at http://www.tonyreynolds.com and I can be emailed at tony@tonyreynolds.com for more info.

Great site, wish I were closer. Happy crystallizing!
Tony, firing in Prescott Arizona

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Erik

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Reply with quote  #9 
We're finding out it's not easy to just switch kilns. Chuck and I wanted to try a reduction firing, so we loaded up the smaller Gile kiln at the studio and fired under our normal firing schedule in oxidation. After the soak was finished we think we could see crystals on a pot through the peephole. We then put it into a heavy reduction for about 30 minutes and shut off the kiln. The books we have don't say a lot about reduction firing, but one book said a reduction at about 1400 degrees worked for him. I'm not sure if the reduction right after the soak killed the crystals, or if there were just very few to begin with, but we ended up with a kilnload of some really ugly pots. There weren't very many crystals, and the copper green glaze that looks great in oxidation looked like it hadn't quite matured, even though the cone (10) was down nicely.

After thinking about it there's lots of things we figure could have affected the firing that we hadn't really considered. The electronic control was clicking on during the soak about every 8-10 seconds for a few seconds at a time. I'm not sure that such rapid short soaks kept the kiln in oxidation, although I would think that the heat would draft it pretty well and draw in new oxygen. I'm also not sure that the reduction so soon after the crystal growing period wouldn't cause the crystals to give up oxygen atoms and sort of 'un-grow' the crystals. (I'm not sure that's even possible).

One of our blues did turn out with some nice crystals, but we only had a couple tests of all the other glazes we figured wouldn't reduce, but for a cobalt mix glaze we got silvery crystals on a blue background, where in straight oxidation we usually get blue crystals on a rutile-y background. Also an iron mix glaze that's similar to the cobalt gave us an almost metallicy temmoku black with a couple, tiny dark crystals

Anyway it's a lot to think about, but it's a learning process. The only problem is we're walking the line of hating to fire a kiln half full, and taking a whole kiln load of work a ride on the experimental train.

When I get back in town I'll post a picture or two

jessehull

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Reply with quote  #10 

Hello,
If your interested in crystalline glazes and firing, I invite you to
visit my site.  You'll see lots of crystalline info, images, and links.
 
I saw some mentions on ^6 crystallines in posts by people wanting to try them. 
I performed many ^6-8 crystalline firings while back in school, did mostly ^10 for five years after that, and I currently fire in the ^11-12 range.   As was the case with me, I was limited by the school's kiln at the time.
But my opinion on this is that if you're kiln can do it, it's much better to learn around ^9-10.  Even ^8 achieves enough heatwork to help in many ways.   Later, once you've gotten the hang of it, you can try altering the unity formula of many available glaze recipes to compensate for the loss of benefits occurring at temperatures higher than ^6.  The key thing to consider is that in order to compensate for that loss, you'll be adding flux.  The only way to do this is to take away from the batch components necessary in making Zinc-Silicate crystals... the zinc and silica.

I was especially interested in the last post by Erik.  Firing in a gas kiln is tricky...  In terms of your glazes looking under fired, I'm guessing that you may have volatized the zinc right out of the glaze.  If you went into reduction at any point during the upward ramp to peak, on your way down, or at the hotter stages of your crystal growing holds ... *poof*.  You'll get a nasty rough surface with few if any crystals. 
Erik, you write that you were using a Geil kiln with an electronic control?  Could you tell me the model of the Geil you were using?
BTW, there's a 10 cu.ft. studio Geil coming out  --it's in the testing stages now. 

~jesse.


Erik

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Reply with quote  #11 
Sorry for the delay in keeping up on this thread, I had a medical hiatus for the last year and am trying to pick things back up where I left off.

I'm not sure about the model of the kiln, I can look at it tonight when I'm out at the studio, if I remember, but it's along the lines of a DL-60(?).

I'm set to try again as soon as I get some new stuff thrown, and I'd really like to find out if I can fire in the gas kiln before I finish my studio at home so I know which way to go in purchasing (or building) a kiln of my own.

As for the results we got in the gas kiln we ended up getting this: (which people say isn't bad, just not what I wanted)



instead of this:




But it wasn't a total failure, as we did get one tiny test piece with something different than in the electric kiln:



I've got some more pictures of some of the items I had during the Holiday Sale if I get them organized I'll try to get some of them posted.

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