Make Slip From A Thick Gritty (Heavier Particle) Clay?

[jnapier]

Hey guys,

 

I have a solid clay with a nice speckly grit to it that I want to cut up, dry out, and make into a slip but I was told theres a risk the heavier particles like grit etc may sink to the bottom when casting.

The company also mentioned there may be not a whole lot of clay content in the clay and I would need to add more - but they had never tried it either.

 

Can someone suggest if any of these is a good solution-

 

a ) break down the clay, add water etc to make the slip and use Epsom salts to thicken clay after?

 

b ) combine TWO clays (both stoneware, one with no grit), dry them, break them down and make slip to help suspend the particles?

 

c ) or would just the usual suspend a few drops of Sodium Silicate or Dispex suspend the particles enough?

 

Obviously I'll experiment regardless but any help would be appreciated.

 

Thanks!

[neilestrick]

Yes, if you cast with a gritty clay, a lot of the heavy particles can sink to the bottom of the casting. If you screen the slip to get rid of any grog, you also run the risk of screening out the speckles and any of the larger particles of clay, like if there's fireclay in the mix. I'm not really sure what they mean by not a lot of clay content and needing to add more. That would just screw up the clay formula. Porcelain doesn't have a whole lot of clay in it, but you can cast it just fine.

 

In response to your specific questions:

a ) break down the clay, add water etc to make the slip and use Epsom salts to thicken clay after? Huh? Why would you need to thicken it back up? I'm not sure what you're getting at here. You don't want to add epsom salts since you're going to have to make a deflocculated slip in order to cast it.

 

b ) combine TWO clays (both stoneware, one with no grit), dry them, break them down and make slip to help suspend the particles? This would definitely help, but I think you'll still see some settling.

 

c ) or would just the usual suspend a few drops of Sodium Silicate or Dispex suspend the particles enough? See a). You're going to have to make a deflocculated slip. Deflocculating won't help keep it suspended.

 

I have a feeling if your slip is thick enough to keep the speckles and grit suspended during the casting process, then it's going to be too thick to cast properly. Your best bet when casting is to use a smooth slip. Hopefully someone else will chime in with some ideas.

[bciskepottery]

d)  go ahead and make a slip of your gritty clay; set it aside.  Use a smooth stoneware slip to make your slipcast items.  After release from the mold and leatherhard, stir up the gritty slip and dip the slip cast item in the gritty slip.  You'll likely need to practice to find the right stage of leatherhard for dipping the slipcast items.  But this will give you the surface you want, but avoid the problem of settling.