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OffCenter What status?
Posts I've Made
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In Topic: What Do You Pug?
Posted 24 May 2013
JBaymore, on 23 May 2013 - 08:15 PM, said:OffCenter, on 23 May 2013 - 08:04 PM, said:JBaymore, on 23 May 2013 - 06:25 PM, said:OffCenter, on 22 May 2013 - 07:21 PM, said:I use a lot of different clays, but probably the one I use the most is cone 6 B-Mix. I think that's the problem. My reclaimed clay has no clay from throwing water and slip that has been dried.
Jim,
You likely are right is the is cone 6 B-mix.
One of the problems with using commercially prepared "stock" clay bodies is that, because they are proprietary formulations, the manufacturers will not share the actual recipes. So we really do not know what is in there and what the proportions are. Makes troubleshooting difficult.
That being said, in order to get a cone 6 clay to really vitrify, the usual high fire (cone 9-10) kind of choice of a potash feldspar to supply the fluxing oxides for the body is not ususally going to work all that well. The proportions of fluxing oxides relative to silica and alumina in feldspars is not ususally providing the "oomph" to get the melt active within the body matrix. So to accomplish this task, the usual "substitution" that happens is to use some or all Nepheline Syenite as a partial or full substitution for a potash feldspar contribution in the body.
Nepheline Syenite is a SODA based material. THIS is where the potential issues begin. The potential issue with this is that Nepheline Syenite is slightly soluble in water (great for carbon trap shinos). And as the Ph of the water supply in the clay body changes.... the level of this solubility changes too.
So....... what I am driving at here is that it is possible that the older clay that has sat around a long time wet before use, and then wet formed and then slowly dried, and then picked up atmosphereic moisture when it was "dry", and then had water from YOUR water source (not the suppliers.....which MIGHT be Ph controlled) added to it.... the water chemistry of the re-mixed body is subtly changing as some sodium ions disolve out of the neph sy content.
This will cause the clay to go "short"...... and eventually when it gets bad enough exhibit some thixotropic qualities. So that might be part or ALL of what you are describing. It fits the situation that the beer and organic stuff growing does not help.
If you are not using a splash pan (like I do not) that likely means that you are throwing pretty dry (like I do). With your skill base, I am guessing that you are a pretty qucik thrower..... not working and working and working and working a piece to death. It seems to me that kind of forming profile would NOT wash out a huge amount of the finer particle clay materials to the extent necessatry to cause the shortness. THAT answer does not make sense to me.
Out of curiosity, do you find that if you let the bags of clay you get from the supplier sit around for a LONG time wet, and that the clay exhibits any similar "short" characteristics? Is it more plastic when you just get it than it is a year later (you might not order that far out)?
best,
........................john
Thanks for replying, John. What you say about Neph Sy is very interesting and yet something else to consider. Commercial clay like B-mix rarely gets to be more than 5 or 6 months old but I've don't recall noticing any difference in plasticity between bought clay that just arrived and clay that I've had 6 or so months.
Jim
Jim,
If you are game.... try running a coule of FRESH bags of the B-mix thru the pug as an experiment... and see if it "kills" the plasticity. My guess is that it will not.
If it is this neph sy solubility factor........ the longer the clay sits wet... the more the issue will evidence itself. Your accumulated scraps ageing is actually possibly making the matter a bit worse.
best,
.....................john
Will test it. Thanks much.
Jim -
In Topic: What Do You Pug?
Posted 23 May 2013
JBaymore, on 23 May 2013 - 06:25 PM, said:OffCenter, on 22 May 2013 - 07:21 PM, said:I use a lot of different clays, but probably the one I use the most is cone 6 B-Mix. I think that's the problem. My reclaimed clay has no clay from throwing water and slip that has been dried.
Jim,
You likely are right is the is cone 6 B-mix.
One of the problems with using commercially prepared "stock" clay bodies is that, because they are proprietary formulations, the manufacturers will not share the actual recipes. So we really do not know what is in there and what the proportions are. Makes troubleshooting difficult.
That being said, in order to get a cone 6 clay to really vitrify, the usual high fire (cone 9-10) kind of choice of a potash feldspar to supply the fluxing oxides for the body is not ususally going to work all that well. The proportions of fluxing oxides relative to silica and alumina in feldspars is not ususally providing the "oomph" to get the melt active within the body matrix. So to accomplish this task, the usual "substitution" that happens is to use some or all Nepheline Syenite as a partial or full substitution for a potash feldspar contribution in the body.
Nepheline Syenite is a SODA based material. THIS is where the potential issues begin. The potential issue with this is that Nepheline Syenite is slightly soluble in water (great for carbon trap shinos). And as the Ph of the water supply in the clay body changes.... the level of this solubility changes too.
So....... what I am driving at here is that it is possible that the older clay that has sat around a long time wet before use, and then wet formed and then slowly dried, and then picked up atmosphereic moisture when it was "dry", and then had water from YOUR water source (not the suppliers.....which MIGHT be Ph controlled) added to it.... the water chemistry of the re-mixed body is subtly changing as some sodium ions disolve out of the neph sy content.
This will cause the clay to go "short"...... and eventually when it gets bad enough exhibit some thixotropic qualities. So that might be part or ALL of what you are describing. It fits the situation that the beer and organic stuff growing does not help.
If you are not using a splash pan (like I do not) that likely means that you are throwing pretty dry (like I do). With your skill base, I am guessing that you are a pretty qucik thrower..... not working and working and working and working a piece to death. It seems to me that kind of forming profile would NOT wash out a huge amount of the finer particle clay materials to the extent necessatry to cause the shortness. THAT answer does not make sense to me.
Out of curiosity, do you find that if you let the bags of clay you get from the supplier sit around for a LONG time wet, and that the clay exhibits any similar "short" characteristics? Is it more plastic when you just get it than it is a year later (you might not order that far out)?
best,
........................john
Thanks for replying, John. What you say about Neph Sy is very interesting and yet something else to consider. Commercial clay like B-mix rarely gets to be more than 5 or 6 months old but I've don't recall noticing any difference in plasticity between bought clay that just arrived and clay that I've had 6 or so months.
Jim -
In Topic: Proportions
Posted 23 May 2013
I like it. For me the weak parts are where you make cut-outs. The bowl shape is strong, the donut in the center is strong and the piece on top is strong. The decoration is nice. The two pieces that have cut-outs, especially the bottom one are weak. By weak I don't mean they need to be bigger, thicker or stronger (even though Big Lou is right about the bottom), I mean a stronger form for the eye. It's the edges of the cut-out that are a problem. Even smoothing and rounding those edges would help some, but it needs more than that. With that said, let me repeat that I like it.
Don't over think it. Walk away from it for at least a day and look at it with fresh eyes.
Jim -
In Topic: your galleries
Posted 23 May 2013
celia12345678910, on 23 May 2013 - 11:48 AM, said:I finally have a little time to read the posts in the communities, and I love that there are so many talented people in the group. I notice that when I view profiles it helps to visualize and TRY to solve problems if I can get an idea of what the final products you make look like. Please take advantage of the gallery benefits of your Ceramics Arts Daily accounts. This would be of good use for people that don't have web pages, and at least Ceramics Arts Daily participants can view your work. Never know, might work like free advertising!OH! I FORGOT! Please let me know when your update your gallery!
Nice piece in you profile gallery. I'd like to know more about it.
Jim -
In Topic: Videos of people making relief decorations in monochrome...
Posted 23 May 2013
JBaymore, on 22 May 2013 - 03:29 PM, said:The relief work on good Yixing is not sprigged. Each element of such designs is hand done with remarkable precision (and the ability to replicate items at a very high level).
I was watching an undergrad class on a very similar type of surface technique at Wuxi Institute of Arts and Technology (in Yixing) a couple of weeks ago, and the painstaking time taken with every movement and the intense focus of each student was what struck me the most.
While the cheap stuff might involve sprigging.... the decent pots don't.
WuxiInstitute-SurfaceDecoration1.jpg
WuxiInstitute-SurfaceDecoration2.jpg
best,
..............john
Maybe when you don't have anything else to do (imagine an emoticon of your choice here), you could post about your trip. I know I'm interested and I bet a lot of other people here are, too. Pictures like those here are fascinating.
Jim
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Comments
OffCenter
18 May 2013 - 09:54Marcia Selsor
18 May 2013 - 07:57OffCenter
06 Apr 2013 - 08:00Idaho Potter
05 Apr 2013 - 19:28OffCenter
13 Dec 2012 - 10:08TJR
12 Dec 2012 - 17:44Tom Roberts
nancylee
14 Nov 2012 - 06:17