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Post by Arnie Benton on Aug 24, 2015 18:36:12 GMT -6
Never.
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Post by evan cornish-keefe on Aug 25, 2015 0:09:47 GMT -6
I believe adding 32 would only work at 0 Celcius. °C x 9/5 + 32 = °F Since I wasn't taught math in art school I just google 1950F to C = ? You're holding within a four degree range?? I hold within a 200 degree range 1950-1750, cone 6 crystals can grow above and below these temperatures but i have barely varied that far because they got rough or matted respectively. willemite.tumblr.com/post/107130117605/rough-crystals
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Post by jfox on Aug 26, 2015 18:06:35 GMT -6
the 32 is the offset 0 degrees C = 32 degrees F so its always in, then C is 5/9 of F
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Post by tileman2 on Aug 27, 2015 21:30:15 GMT -6
Evan: You misunderstood my post, although I was not very clear. My top ramp hold runs between 1932 to 1936; and the second ramp is usually around 1840-1860. Depends what colorant I am using.
Tom
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Post by tileman2 on Aug 28, 2015 22:23:16 GMT -6
Been working on a cone 6 glitter/snowflake effect glaze. Getting closer- picture does not show the gold glitter very well. Has the appearance of matte in some aspects, but is in fact glossy. After mixing the glaze batch, I came back and added 10% frit. It did seem to cure the problem with crystal courseness. Not sure how much that would help the vertical pieces; but it did work on flat work. Tom
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Post by tileman2 on Aug 29, 2015 22:09:31 GMT -6
After two years of playing: final results on cone 6 recipe. 2230F 3 hrs first ramp / .45 minutes second ramp. Largest crystal size: 3.75" inches. No grazing, or clay/glaze interface checking. .50 Co Carb .50 Co My final recipe: time to redo my color pallet. Tom Tile Art Studios
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Post by evan cornish-keefe on Aug 29, 2015 23:49:31 GMT -6
Hey Tom, Yes I definitely misunderstood, i should have assumed that from your images I suppose. The glittery green glaze looks interesting, lots of Ti or rutile? Here's a mug with Sphene (aka Titanite) crystals: fired a bit under cone 6 on Little Loafers clay: 400/hr - 2000f, 108/hr - 2216, 600/hr - 1950f, 50/hr - 1750f ff 3134 - 30.08% Lith. Carb. - 16.26% EPK - 21.95% Flint - 31.71% + TiO2 - 11 CoC. - .5 The outside was sprayed with a nickel bearing zinc crystal glaze, the overspray caused the goose-poop green.
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Post by tileman2 on Aug 30, 2015 12:10:18 GMT -6
Evan Have a similar bowl/crystal using Neodynium. Yes- - lots of rutile in the glitter flake.
Tom
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Post by tileman2 on Sept 13, 2015 20:52:14 GMT -6
First I had to make some Ilmenite fondue- so I could get it to melt at 2230F then added that to rutile and .50 CO.. pre-planned this piece for reduction. Had to reduce the ZNO slightly to get rid of the over-population of crystals. Add this piece to the collection of pieces I am going to try a new method of reduction on. Tom
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Post by evan cornish-keefe on Sept 15, 2015 9:28:00 GMT -6
The bottom of this bowl is rough enough to cut yourself on, crystals growing over 1/8th inch above the glaze surface. The same glaze has been smooth in the past, but on a different clay and in a kiln/cooling cycle...?
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Post by tileman2 on Sept 15, 2015 13:56:06 GMT -6
Evan: Must say this is a real oddity. Assuming I am looking at FE and MNO? The one issue I see in both pieces are small white pin-dots. I see them all over the center of the first piece, and scattered on the second piece. The first picture looks like multiple nucleation spots around the outer rim of the crystal- almost burnt looking. Would guess at this point sodium or potassium being leached from the clay- this is a tough one to call.
Tom
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Kuba
Full Member
SztukKilka in Old Formu
Posts: 111
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Post by Kuba on Sept 15, 2015 13:59:05 GMT -6
It looks like a razor blade
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Post by tileman2 on Sept 15, 2015 16:20:44 GMT -6
Evan: This is the reason I think the problem is (caustic) levels of sodium. Could be other things, but this is a tile I used caustic sodium to test reactions of high levels of salts. Same raised sharp spikes, same black/burnt looking appearance. Sorry for no close-ups, but the white specks are also present. Someone else might have other insights- but from my experiences. Tom
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Post by evan cornish-keefe on Sept 16, 2015 20:27:34 GMT -6
Hey Tom, It's Fe and Ti. The white spots are just highlights from the camera. Interesting idea about sodium, what would be a caustic level? And would lithium/potassium have a similar impact? The metallic glaze above has lots of lithium but not so much sodium. I smashed one of these bowls trying to see the profile, the pool of glaze at the bottom was very thick, much more than I had thought. Do you remember the cooling cycle of your caustic sodium test?
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Post by tileman2 on Sept 16, 2015 21:29:32 GMT -6
Evan:
The test piece shown is 13.73 PH- not 10.73 as noted. Alkalinity above 12PH is considered caustic. Potassium and sodium are considered salts; Lithium is considered a metal. Potassium is less corrosive as sodium: sure you have noticed that when you have thrown or handled clay that uses sodium feldspar as a flux. Having read extensively about lithium: it is most active as a flux between 2150 to 2230F, and decomposes between 2260-2300F. That is the general range; some suggest lower temps, and other higher: so those are the medians. From my testing notes on cone 6 lithium additions: 3-5% should be the max at 2230F. 2-3% produces a PH of 10.60 to 10.70 and 3-5% produces a PH of 10.70 to 10.90PH. So the percentages of Lithium above 3-4% do not change the PH level; it only increases the saturation level. Higher percentages of lithium does effect the reactions of sodium and potassium in the glaze from my studies. If the potassium or sodium additions used in conjunction with lithium are above the caustic level; then a reaction should be expected. It would most certainly create boiling in the glaze, which could account for some of the raised areas: but more likely pinholes that would mostly heal at soak temps. My 6.5 top loader is 3" brick with 2" fiber board; by design it cools very slowly- so I do not program a cooling ramp. On cone 6 my first ramp hold runs between 1935 up to 1942, and on cone 9 my first ramp hold runs between 2024 and 2028 pending colorant. Sodium reactions, and most often potassium reactions present themselves as white/grey spots or blotches, blackened nucleation sites, and they will also produce white/grey needle crystals. If you had high levels of lithium and some sodium in the pieces shown: then you had an extremely fluid glaze at 2230F- which accounts for the excessive pooling of glaze. Which also means the lithium and sodium ran to bottom as well: which was probably boiling like water at peak temp. Lots of info-
Tom
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