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Post by John Garrison on Oct 13, 2016 13:42:05 GMT -6
This is just a theory, but, correct me if i maybe wrong with this. I have noticed at peak temperature around ^10 / ^11 if there is a hold greater than lets say 10 mintues, the below crystals form with the presents of certain materials. Now the reason i have this theory is for this reason. When the temperature was not held with the same glaze makeup, these below crystals did not form. When the hold was greater than 10 mintues with the same glaze, they formed. Same environment/clay/schedule.. etc The only reason i have not seen this anywhere else if because... well no one likes holding their kilns at or past ^10 for any amount of time if it can be avoided. Thoughts...?
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Post by John Garrison on Oct 13, 2016 13:46:40 GMT -6
Facts we know:
Typical zinc silicate growth temperature is between 1850 and 2000.. roughly dependant on glaze make up and amount of flux.
This can not be the only temperature that can be worked with.. but holding at a higher temperature typically results in glaze run off and other undesirable defects
Could this be uncharted territory?
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Post by mohawkpiper on Oct 14, 2016 22:46:06 GMT -6
i could be totally wrong but i feel it doesnt necessarily have to do with the hold length directly but more with how much you are fluxing the glaze, which is resulting in different glaze thicknesses. i feel crystals will have different shapes in different glaze thicknesses even at the same temperatures. i havent gotten any crystals like the ones you posted but i am pretty sure nickel secondaries grow in specific thicknesses given the glaze has the right ingredients for it. we get nickel and titanium secondaries on some pots and not others all in the same firing. i believe it to be due to differing thicknesses in the glaze.
try fluxing your glaze out some and not doing a hold at all and see if u still get them.
also i believe crystals grow in a wider range than u suggest, more like from 1700F to 2150F and maybe even a wider range than that.
G
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Post by mohawkpiper on Oct 14, 2016 22:51:12 GMT -6
mind you peak temp is just a temp, not a cone. a cone is heatwork so temp plus time. by adding time u are raising the cone but keeping the temp the same. the cone reached at peak can be altered by all sorts of variables even if u hit the same temp every time. from rate of incline, to hold time, to size of kiln, cooling rate, how loaded the kiln is etc etc
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Post by John Garrison on Oct 15, 2016 10:21:13 GMT -6
The crsyals i get have been consistent through out all parts of the piece, at the top where the glaze is thinner and at the bottom where it is thicker. The below photo is one i found today which could very well prove my therory. You can see the center of this crsyal is black then what im assessing this that when i dropped my temp down to around 1850 the crsyal started to form as we all normally see them. You can even see where the change happens at the drop. Im going to continue this testing and see it i continue to get them. My next fire I'm going to do a longer hold and see if they get bigger.
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Post by John Garrison on Oct 15, 2016 11:49:58 GMT -6
Regarding my grow temp range reference, I just used that as kind of the "optimal range" otherwisw at the hotter end you get splinter like crsyals and the lower end they can become underdeveloped. You're right though the range is a bit wider than what i put.
-John
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annie
Junior Member
Posts: 55
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Post by annie on Oct 16, 2016 2:18:43 GMT -6
John, Isn't it more likely to be "the presence of certain materials" and heat work rather than the temperature itself. I hold all the time for 10 to 20 minutes at my top temperature to reach cone 10 to 11 (usually cone 10.5 if you will in the bottom half of my kiln) and I don't get that centre. It's lovely. Looks feather-like and beautiful.
I'm with Greg in thinking you could add more fluxing materials to you glazes and replicate the same sort of look at a lower cone. I don't think it has to do with ten minutes held at your top temp really.
Or add some lithium to drop a cone or two and see.
I won't ask you what the certain ingredients are but think I've seen these shapes with moly in others' photos.
Keep up the great work; love to see the full piece, too. Take awesome notes so you can duplicate!
--Annie
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gczop
Full Member
Posts: 202
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Post by gczop on Oct 16, 2016 9:00:02 GMT -6
Very interesting, would you care to share your glaze composition? Would appreciate a photo of the entire crystal. For other ground breaking crystals see the Microcrystals thread by Evan Cornish Keefe. Good luck, Gordon
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Post by John Garrison on Oct 16, 2016 9:37:04 GMT -6
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Post by jfox on Oct 16, 2016 10:44:00 GMT -6
Ive always had the sense that those dendritic crystals were associated with higher temperature holds after prolonged lower temps and grow from the center of previously grown crystals by feeding off of them,but as with all things it seems the more you learn the more you realize how little we understand
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Post by John Garrison on Oct 16, 2016 14:24:03 GMT -6
It would be great to have a camera that i could stick in the peep hole to confirm or deny my theory, I am aware they are out there. I too believe we only know a small fraction of how crystals form in respects to ceramic glaze.
Yes, we know a fair amount about zinc silicate, but, there is far more to it than what i think we currently know. The possibilities are endless.
Im thinking these grow at the initial top hold due to photo 2 i posted. Also due to some of them looking as though they were there before i hit my usual grow temo/hold. Some seem to be rocks in a steam as the zinc silicate crystal grows around them in some places.
Im going to measure these and do another fire with a longer hold at my top temp to see if there is any growth past my current fire.
-John
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annie
Junior Member
Posts: 55
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Post by annie on Oct 17, 2016 7:15:41 GMT -6
Hi John, I woke up this morning thinking, "I wonder if I have any of those black snowflakes at the start of my crystals?" And voi la! I found a couple on a flat piece and I had held at top temp for 20 minutes in this particular firing (and I've not tried Molybdenum).
I'll try to figure out how to post the pic. What I'm wondering though is if it's just a coincidence that we held at our top temp or if it's related to the first hold temp and the raw materials? Be interesting to see what you're tests reveal. Mine are so small I hadn't even noticed them, but found my digital camera has a macro setting I wasn't even aware of. I'll put them up if I can get photobucket working.
Thx for pointing the black beauties out! -Annie
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annie
Junior Member
Posts: 55
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Post by annie on Oct 17, 2016 8:05:59 GMT -6
Hi John, Here's one image (if I did this correctly): and another: and the test piece (coaster) entirely: The second 'black snowflake' can be seen without amplification in the bottom portion of the coaster, about 3/4" in from the rim, at about 5 o'clock. Haven't a clue if this will work. Fingers crossed! -Annie
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Post by John Garrison on Oct 17, 2016 16:49:36 GMT -6
Annie,
Thats great to hear you're getting these too. Unfortunately, I am unable to view the photos you posted :/
-John
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Post by tileman2 on Oct 17, 2016 17:59:02 GMT -6
Hi John:
Have always wondered if sodium was the cause? Sodium crystals can form as well: and usually have that milky white look to them. Zinc crystals are hexagonal; giving it that fan look of fine needles. Sodium crystals are cubic: thready and course. I use to get these type on occasion years back before I changed my recipe to remove impurities. Impurities are usually burned off (decomposed) in a high cone 10, but are very much in your face in a cone 6. Gordon's avatar is an example of a sodium crystal. That same bluish/milkish color around the course needles is present in your samples: although not that pronounced: but then again your sodium levels are much lower.
Tom
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