Slurry Mixing Clay Bodies

My Process

I mix 10 pounds at a time because America πŸ‡ΊπŸ‡ΈπŸ—½! I think all pottery suppliers in America sell dry materials by the pound, with the exception of bags of foreign materials, which come in 25kg bags.

10 pounds of dry materials makes around 12 pounds of wet clay. It's a nice amount to make several test pieces or one large vase if the clay is for throwing big. At the same time, 10 pounds isn't too much of a waste if the clay turns out bad.

  1. Measure out dry ingredients
  2. Add dry ingredients to a 5 gallon bucket except for bentonite
  3. Add at least one gallon of water (8+ lbs)
  4. Mix with power drill, slowly adding bentonite
    1. It's very important to make sure the bentonite does not clump
    2. Mix well until all clumps, ball clay and bentonite included, are dispersed
  5. Let slurry sit overnight
    1. Drain the excess water after the clay settles a bit
    2. May be necessary to sit for several days to decant enough water
  6. Dewater clay on a plaster slab
    1. I also run a fan over the drying clay to speed up drying, especially in winter
    2. Wedge clay after it stiffens
  7. Age clay
    1. I don't add anything extra to the clay, just bag it and store at room temperature
    2. If the clay isn't mixed well, plasticity increases a lot over the first few days
      1. I don't see much value in aging for months or years. A 1% addition of bentonite is enough to make most clay very plastic (or up to 3% in the case of kaolin only porcelains)

John Tilton's Notes

From his Instagram on mixing 10 gallons of Porcelain 022924:

  1. Add 11 inches of water to a 10 gallon Brute Container. This is only approximate because water may have to be added during the mix.
  2. Slowly add 191 grams of Macaloid and 191 grams of Bentonite-L to the water as it is blunging. My blunger has 3 different propellers, each 3 inches in diameter, and I only use 1 down facing propeller at this stage, so the propeller is guiding the liquid down.
  3. Mix for 2 hours to turn the mixture into a gel. Maybe not a true gel, but basically these materials can not be taken out of this solution anymore and they don't settle to the bottom.
  4. Add 1 quart of slip from the slip bucket. This slip bucket has been going for over 40 years, and I want to start bacterial action with this slip. Blunge 1 hour. - I forgot to do this on this batch. I had just recycle all the slip in the slip bucket, so there was no slip, but I did add a quart of slip bucket of water after all the clay was in. I poured the water through a 100 mesh sieve.
  5. Measure out 4 pounds of Grolleg Kaolin, add to bucket, and blunge for an hour.
  6. Measure out 9.1 pounds of 200 mesh Silica and 4.9 pounds of G-200 EU Feldspar. Add the up facing propellor to the shaft and adjust the height of the propeller. and add the Silica, and Feldspar to the bucket. Blunge 2 hours. Make sure everything is mixed up by taking the shaft off the mixer and gently scraping the sides and bottom of the bucket and seeing if there any clumps. Mix those clumps into the slip.
  7. Screen the slip through a 100 mesh sieve. The slip is still very watery. so it goes right through the sieve. What is left on the sieve appears to be mica from the Feldspar and larger pieces of Silica from the Silica, and organic matter from the bags being outside. and I want these removed from the clay.
  8. Add the third propeller and ad the final 10.3 pounds of Grolleg. I add the Grolleg slowly and shake the bucket to get the Grolleg to mix in to the water. If needed the height of the propellers is adjusted, and more water is added, but this mixture is already a couple inches from the top of the bucket, so I can't add much water and still be able to move the bucket around. Make sure that all materials are mixed in by removing the shaft form the motor and probing around with it.
  9. Blunge 2 hours.
  10. Add 44.5 grams of Epsom Salts dissolved in hot water. Pour the Epsom Salts though a 100 mesh sieve.
  11. Blunge another hour.
  12. Allow slip to sit for a few days, taking water off the top and adding it to a bucket waiting to be used for a new batch.
  13. Add slip to clay drying rack and wait for it to be dry enough to remove. This is a few days. The slip in the clay drying rack will dry faster on the ends, so take that out first. When the clay is dry enough to stand up, unstick it from the sheet and stand it up in the clay drying rack. It will dry much faster standing up.
  14. When the slip is dry enough,, make arches and set them on the porcelain wedging table. Monitor them and when they are dry enough, pug them and put them away in Brute Containers.

Abridged

  1. Add Macaloid and Bentonite-L. Blunge for 2 hours.
  2. Add slip for bacteria culture. Blunge for 1 hour.
  3. Add Grolleg Kaolin. Blunge for 1 hour.
  4. Add silica and G-200 EU feldspar. Blunge for 2 hours.
  5. Pass slip through 200 mesh sieve.
  6. Add additional Grolleg. Blunge for 2 hours.
  7. Add Epsom Salts. Blunge for 1 hour.
  8. Let sit for several days.
  9. Drain excess water and dry on rack.
  10. When dry enough, pug.

Notes

Drying occurs in two main stages: 1. Slurry to soft clay 1. This happens relatively quickly on a plaster slab. 2. If plaster slabs are limited, remove clay immediately after it releases from the plaster and air dry. 2. Soft to stiff clay 1. Throwing with soft clay is very difficult and should not be mistaken for low plasticity clay 2. This part can take especially long for highly plastic clay

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