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Post by Arnie Benton on Oct 19, 2015 7:13:32 GMT -6
Hi Tracey -
I haven't been putting any glaze on the bottom or outside of my plates and bowls. That could be part of the problem, but I've been doing crystalline glazing for the past 10 years and the cracking and breaking are much worse now. Probably related to the change in feldspar in the clay that's been written about. I have used a non-running stoneware glaze on the outside but not the bottom. I'd have to go back through old records to see what breakage there was then.
Putting Silica sand under the foot does seem to help.
Arnie
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Post by tileman2 on Oct 19, 2015 16:42:35 GMT -6
Arnie:
Ran a clear base cone 10 stoneware and a very basic cone 10 crystalline on digital-fire for expansion coefficients.
Cone 10 Base Glaze --- C.O.E. = 4.91 Cone 10 Crystalline -- C.O.E. = 7.55
Tom
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Post by Arnie Benton on Oct 19, 2015 18:08:10 GMT -6
Tom - So maybe it's better not to put any glaze on the outside and bottom of bowls and plates than to put a stoneware glaze? Or does 'no glaze' mean a COE of 0?
Arnie
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Post by oliverpiano on Oct 20, 2015 13:58:43 GMT -6
A tip of the hat to Arnie. Ni had been one of my favorites as I got nice color and contrast from one colorant and it worked well for me. When I went to 3110/413 and 3110/644 bases I was not able to get Ni to work in either glaze and 3110 w/Ni worked but the crystals were much smaller. I was looking for a couple more color combinations for some small plates that I was making to test and sell as a less expensive item and decided to mix up a couple glazes one w/Ni and a little Fe and Mn and another w/TiO instead of Ni having looked at some of the colorant combinations Arnie had posted and doing something similar but not the same. These plates have the glaze w/TiO for a first coat and a center coat w/Ni and an extra coat of the TiO glaze on the rim and both these plates were just alike coming out of the crystal firing and the second was strike fired.
<img style="max-width: 100%;" alt="" src='http://'>
<img style="max-width: 100%;" alt="" src='http://'> Then I adjusted the glaze for vertical pieces and got this.
<img style="max-width: 100%;" alt="" src='http://'> Thanks Arnie. Mike
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Post by Arnie Benton on Oct 20, 2015 15:11:52 GMT -6
Hi Mike -
Russ yesterday and you today - it's great to have you posting again - I am so happy that you're using my information - and having such a great result - if you try it with a bowl shape you'll probably get the swirls and different colors in the ground as well.
I'm intrigued by the vase - did you put layered glazes on it? I'd like to know how layered glazes work on vertical surfaces, if at all - and what happens if struck -
Arnie
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Post by tileman2 on Oct 20, 2015 16:11:30 GMT -6
Arnie:
So I just ran three different cone 10 porcelain clay recipes that I know of: the C.O.E ran as low as 2.68 and up to 3.12. Your stoneware glaze is a closer glaze fit than crystalline. Crystalline glaze is-well- crystalline glaze. The other solution requires you to spend $50,000 on a piece of testing equipment that measures linear expansion at high temperatures. Let me know- will get one ordered for you-- LOL>
Mike- great NI piece- rather fond of that colorant myself. 4% rutile and .75 NI produces a similar color- but has a lighter yellow field.
Tom
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Post by oliverpiano on Oct 21, 2015 8:33:08 GMT -6
Hi Arnie, The jar has only the Ni w/ a little Fe and Mn. It's in a 3110/644 base that wanted nothing to do with Ni by itself but the small adds got the Ni to play well even with 644 in the glaze. It's funny, I was wondering how this glaze would strike and how it would look layered in combination on vertical pieces so I guess I'll have to find out. Tom- I would have thought that with .75 cobalt it would come out blue on blue. Guess I'll have to try that too. I get a lighter yellow ground than the jar shown with just Ni and I like it better lighter but I have had no luck with just Ni in either base I'm using. One more tip of the hat while I'm at it. When I came to the last workshop in Dunedin, I had just started throwing the little spire on top of a trimmed lid from watching Bill Schran add a foot to a trimmed piece that way at my first Dunedin workshop. It worked great until it came to the drying and it was pealing up chunks of clay from the lid as it dried. I mentioned it to Bill Campbell who has more answers than I have questions and he said put it in a covered container with a jar of water to retard drying. Tim Moran was standing there too and had a similar method so now I put them in a plastic bag on a small plastic bat with a wet sponge and seal it for a few days and you see the result above. I love it. Thanks Bill and Tim, Mike
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Post by Arnie Benton on Oct 21, 2015 10:32:36 GMT -6
Tom - Mostly I've been using 11.5 inch bisque bowls that shrink to 10 inches after glaze firing. They haven't broken. Bowls of 12 inch diameter after glazing break maybe 1 in 8 after 2 firings, and larger sizes break more frequently. Hopefully the problems with the clay will get worked out soon. Your numbers show that the glaze/clay are always under some tension - I have played with adding Bo, Alumina, etc to glazes without success.
Mike - The list of potters who've given me everything from a helpful hint to a lifesaver is quite long - and I've done my best to give back - you suggested the brushes I use for applying glaze - I've been using them for years and think of you often - There's no doubt that on my horizontal surfaces layered glazes produce dramatically different results than a single glaze - but that might not happen with all the flow of glazes on vertical surfaces - I hope you do try the experiment.
Arnie
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Post by Arnie Benton on Oct 21, 2015 10:45:51 GMT -6
In going over the results of my last picture posting, I realized I left out an important variation. So, I did it, and WOW! Here it is. This is the same glazes as in the 5 pictured pieces above - there's no engobe and the bowl has layered glazes but with the addition of Ti 2 to the under glaze only. So this would fit between #2 which has no engobe and the 2 glazes without addition layered on - and #3 which has the Ti addition to both glazes which are layered on. All have been strike fired. I'll put pictures of all 3 up here - #2 - no engobe, no additions to the glazes, layered #3 - no engobe, addition of Ti to both glazes, layered New Piece - no engobe, addition of Ti to bottom glaze only, layered and compare this to #1 - the same layered glazes over the engobe which has Ti - So, adding the engobe additions to only the underglaze of the layered glazes on a piece with no engobe seems to reproduce the effect of the engobe. Not adding the engobe additions or adding the engobe additions to both of the layered glazes doesn't give this result. My conclusion is that additions to engobes effect mostly the lower layer of 2 glazes and not the upper layer - and applying just one glaze over an engobe gives very different results - see pictures 4 and 5. At least I THINK this is what is happening - I hope others can follow this discussion - I don't know if what I've written is clear or if I've over explained it. Arnie
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Post by tileman2 on Oct 21, 2015 16:49:15 GMT -6
Arnie: I have to confess your last post has thrown me off the discussion- was following just fine until then. The last two pics were new pieces not posted before- got that. The first two are the ones throwing me off. That aside, the glaze pattern in the new piece is astounding- have seen small patches of it before, but never on this scale. Not sure if there is a technical glaze term- but for the lack of a term: starburst effect. I assume this piece is being shown after striking?
Mike: need to qualify a comment I made above: I get a nice yellow on flat work; not sure it would be the same on vertical pieces.
Tom
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Post by Arnie Benton on Oct 21, 2015 19:22:21 GMT -6
The last piece above has the engobe with 2 layered glazes on top of it, and struck. It produces that starburst or explosive effect in the ground. The third piece has no engobe but the engobe ingredients - Ti was added to the bottom glaze of the layered pair of glazes, then struck - same effect on the ground. The second picture shows that if you add the Ti to both glazes of the layered pair, the ground effect does not happen. (And if you put some Ti in a mixture of the 2 glazes and apply it as one glaze, there is no big effect on the ground after striking). SO, it seems that the dynamic, explosive, starburst, whatever you want to call it, ground, occurs after striking a bowl with layered glazes that has Ti and CaCo3 added to the bottom glaze. The Ti can come from an engobe or be directly added to the bottom glaze of a piece with no engobe.
The next stage of this investigation is to find which oxides in the glazes are necessary to produce the effect. The bottom glaze has Fe Co Mn and Ti. The top glaze has Cu Co and Ti.
Arnie
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Post by tileman2 on Oct 22, 2015 9:09:55 GMT -6
Mike:
After reading your response I realized my mistake: 4% rutile and .75% NI. (not CO). Sorry about that.
Tom
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