: JBaymore - Viewing Profile

trina, on 23 May 2013 - 07:33 AM, said:

It is actually the general rheology and shear characteristice that is dominant in the "plastic" qualities of clay that we use. That old ((but intereting) paper is oriented about flotation qualites and particle disbruisement in thin slutrries... for agricultural sealing use.

best,

....................john

OffCenter, on 22 May 2013 - 07:21 PM, said:

Jim,

You likely ar 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

Chris Campbell, on 22 May 2013 - 04:19 PM, said:

My understanding of this is that the visual appearance (it it truly differes from all others) of the piece may be Copyrighted... but the DESIGN of a functional piece .... must be Patented (a costly procedure)... and prove that it is a "new" thing not previsous "discovered" and already Patented.

best,

..............john

A core idea that I was trying to get across was also that you cannot generalize across the board.... particularly in an R+D situation for serious industrial or quasi-industrial product development. I've done some research for industry....... it is a different "beast" from the typical studio pottery or academic studio situation.

Multiple factors will affect the "strength" of the body. And there are multiple measures of "strength".... you have to assess WHICH of these are important.... compressive, tensile, shear, ruptutre, brittleness and so on.

Bodies are designed for specific forming methods along with otehr characteristics. The same body hydraulic pressed and hand pressed into molds will likely give different strength figures. And so on. Hydraulic dry pressing is one option for what you are possibly seeking, with VERY high possibility mathematical size and strength tolerances.

I'd suggest that you contract the services of a ceramic engineer with skills in clay body development. Even the most skilled ot us "tech weenies" in the "art" field do not have the background that someone with a M.S. in cerramic engineering would have.

best,


............john



PS: yes Yixing clay is not fully virtified. Many clays usee in Asia for stuff like teawares are not.

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 (206.47K)
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 WuxiInstitute-SurfaceDecoration2.jpg (126.24K)
Number of downloads: 26



best,

..............john