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jafa5

Local clay with low plasticity

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I've found a large seam of white clay at work that will be excavated over the next couple of months.  It looked pretty promising so I bisque fired a small bead of and it turned out really well. 

I then fired it to cone 12, just to see and it looks awesome!  So now want to make a few pieces with it and fire them.  The finished fired raw clay looks like tea dust glaze, guessing this is because it's over fired but looks stunning. 

Only thing is its quite short (my mums term for pastry), or low plasticity, so i'm after some information to get me started on researching clay chemistry.

Big topic I know, but potting is a slow game and I might as well start while I have access to so much material. 

Any tips, books or links would be appreciated. 

Cheers,

Liam

 

 

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Ball clay will add plasticity. Is there a temperature at which you'd like to use the clay? I'd fire a test at that temp and see how it behaves so you have a better idea of how much blending you're going to need to make it work for you.

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From your brief description of " tea dust" at cone 12.. And white at bisq cone 06-04?

to survive a cone.12 firing without melting; then the raw clay would be low in natural calcium, sodium, and potassium. Which takes it out of the ball clay class: the low plasticity confirms that. The Tea dust" would come from iron and magnesium levels: but without seeing pics I can only guess at those levels. Ball clay is the go to plasticizer; but you will be adding iron, titanium, and magnesium as well. The % you add will effect the fired color: so is that an issue?

Given the New Zealand address, and the fact it survived a cone 12 firing, and it is white: means your clay has a high alumina content- which is also non-plastic. Would not be surprised if it halloysite that has been naturally contaminated . Is this clay seam in a flat land, higher up, or valley/ drainage area?  I can recommend several routes for plasticity, but would like to see some pics first.

tom

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Sounds like you have a clay that has been transported by water and 'washed' of some of it's most fine particles.

As you have found these 'secondary' clays can work very well as substitutes for Albany or Barnard slips.

A few years ago I entertained the posibility of developing a clay body from a local secondary clay. After asking around and reading a bit I decided to forgo the idea. It just wasn't worth the effort for me.

Even working with known ingredients, develpoing a clay body takes a lot of research and experimentation.

*I assumed the fired result was a tea dust appearance - if otherwise please please disregard my hasty conclusions. As Tom suggests pictures will help.

Linda Arbuckle has a good primer on clays and clay bodies.

Just in case you have a fear of slimy things and wonder what to call it.

I've had that last one for a while. Koniophobia (the fear of dust) has become more of a healthy attitude than perhaps a paranoid obsession.

Edited by C.Banks

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Thanks for the responses and sorry for my late reply, crazy week :)

I'll start with the bally clay and make some small batches up with increasing increments and post the results with some photos.

My mate took a sample home last week and has mixed that up with ball clay and a little bentonite and is firing this weekend so will hopefully have some photos from that.

The seam is about 15m thick in rolling country and sitting on top of Pakiri formation rock.  Its at the top of the hill and down the bottom, the section we are cutting is in the side of the hill, maybe 30m from the top and 50m from the valley.  Other areas near by where we have cut in small areas appears to have the same material though.  I'll check my phone to see if I have photos of the seam.  There is a halyosite mine around 20km away so definitely in the local area.  Funnily enough the material from site looks very similar to the stuff in my bottom paddock so might be a nice long term project working on that.  Appreciate it's a lot to learn and heaps of mistakes to be made but I like a challenge.

Bisque firing was to 950°C.  Yes the firestorm result at cone 12 was a tea dust surface on the clay but no distortion or melting.  Unfortunately not had time to make another firing yet but the clay sample is now well wetted down.

I'll find the photos and post them up this arvo.

Thanks for the links, will get into this this arvo too.

Cheers, 

Liam 

 

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