Rhett ParhamFine Art Ceramics · Kaʻū, Hawaiʻi Island

Uncle Rhett's Studio · Kaʻū

Uncle Rhett's Ceramic Slip Recipe

Turn your clay scraps into smooth, sticky slip for joining, decorating and texture. One tub per clay body, a blender, and a capful of apple cider vinegar.

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What you need

  • Clay scrapsTrimmings, dried bits and failed pieces, sorted into small tubs: one tub per color or clay type. Label each tub.
  • WaterEnough to cover the scraps and soak them down to a quicksand-thick, pourable mud.
  • 1 capfulOrganic apple cider vinegar (a cap is about 1–2 tsp) per full blender.
  • BlenderA studio-only blender. Once it blends clay, it never goes back to the kitchen.
  • Lidded jarsTo store the finished slip, labeled with the clay type.

Make it

  1. Sort your scrapsWhen you finish a session, drop the scraps into the tub that matches that clay. Keep colors and clay bodies separate.
  2. Soak to quicksandKeep enough water in each tub that the clay slakes down into a thick, pourable mud, about the feel of quicksand. Dry scraps break down faster than leather-hard ones.
  3. Stir and pourMix the tub well to break up lumps, then pour into the blender.
  4. Add the vinegarOne capful of apple cider vinegar for a full blender.
  5. BlendBlend until smooth and creamy with no lumps. Scrape down the sides if needed.
  6. Jar and labelPour into a lidded jar and write the clay type on it.

Start with a half batch

Fill the blender halfway and use half a capful of vinegar. Test the slip on a scrap joint before you make a full jar.

Adjust it

Too thick or pastyAdd a little water and blend again.
Too thin or runnyAdd a few splashes of vinegar. It thickens the slip. Or add more soaked clay.
Not grabbing on joinsA splash more vinegar makes it stickier.

Is vinegar a good idea? Yes.

Vinegar is a mild acid. It makes the tiny clay particles clump together (potters call this flocculating). That is why your slip turns thicker, creamier and stickier with only a capful. That stickiness is exactly what you want for scoring and slipping joins, and it is the same idea behind "magic water."

The vinegar burns away completely in the kiln and does not change the fired color or the glaze.

Good to know

  • A few splashes go a long way. Too much vinegar turns slip gummy and hard to brush.
  • Vinegar slip is for joining, brushing and decorating. It is not casting slip: for pouring into plaster molds you want the opposite, a deflocculant like sodium silicate or Darvan.
  • Only mix scraps of clays that fire at the same temperature. Join and slip with the same clay body as the piece.
  • Stored slip may smell sour or grow a little mold over time. That is harmless to the clay. Stir it back in.

Bonus: vinegar + baking soda textures

Brush or drip vinegar onto slip or wet clay, then sprinkle baking soda (or the reverse). The fizz throws off carbon dioxide bubbles that leave craters, pits and foamy, lava-like surfaces. Change the amounts and the timing to get different textures.

  • Try it on test tiles first and fire them before using it on a finished piece.
  • Baking soda contains sodium, which acts as a flux. Heavy amounts can make the surface slightly glassy or blistered at high temperatures. Light dustings are safest.
  • Let a fizzing batch finish before you put a lid on it. Trapped gas can pop a sealed jar.

Studio safety

  • Clean up slip while it is wet. Wipe or mop; never sweep dry clay. Dry clay dust contains silica you should not breathe.
  • Keep the clay blender, jars and spoons for studio use only.
  • Pour rinse water into a settling bucket, not the drain. Clay clogs pipes.