Electric Mid&Hi Fired Ceramics
Potters & Sculptors - Making Rock from Mud
Darvan/dispersant & slip ..is that the need 4 non-Newtonian thixotropic character reversel in wheelwork.
We have a lot of recycled white slip waste offcuts which I have tried to get to a point through the pugmill to be able to do wheelwork .
I have experimented with added Grogs and Kaolin.
The big problem with the clay, which has been prepared for pouring ,firstly by adding Darvan/ dispersant. Makes a Great slip though! ...is that the non -Newtonian thixotropic character of this clay, because of earlier dispersant added creates a shear factor on the wheel which twists under pressure and is very difficult to centre.
I need to add something chemical etc. to the clay to break the negative charges on the clay particles, to attract rather than disperse. NOTE: If I take an oblong ball of clay in 2 hands and wring slightly, there is a twist of about 2 centimeters before the clay stiffens. Release and you can do it again... the vibration of the wheel also collapses this thixotropically.
Perfect clay though for rolling out.!
Any help will be very welcome please.
Replies to This Discussion
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Permalink Reply by Norm Stuart on
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Darvan traps calcium and magnesium ions in clay and releases sodium ions in exchange, just like a "water softener".
To reverse this, you need to add calcium and or magnesium ions to exceed the Darvan level and flocculate the clay again.
I use calcium chloride, used to melt ice. Many use magnesium sulfate (Epsom Salts).
As the calcium or magnesium flocculates the clay it will quickly "become drier", so test a small batch first to see if you need to add water before adding the calcium. Pour-able slip is actually quite dry.
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