Hint #4 - Preventing Stuck Lids

The Problem
How to prevent lids from fusing to the pots during glaze firing.

When firing stoneware or porcelain it is sometimes not enough to remove all the glaze from the joint between the lid and the piece. In some cases the clay itself fuses, making it impossible to remove a lid without damaging the work.

What I do:

  • Before glazing the bisque ware, I slowly spin the pot on the wheel and brush wax resist on the lid galley of the pot. 
  • The inverted lid's rim is coated with lid wax (lid wax is explained below). This margarine tub (being used as a chuck) actually has sand in it to help anchor it a bit.

  • Once the wax is dry, the piece is glazed. 
  • It is essential to sponge every bit of glaze off the wax. Any small beads of glaze will fuse and the lid breaks when removing it after firing. 
  • With the porcelain I use, I have to coat both parts (the pot and the lid) with a special lid wax. 
Making Lid Wax
  • Lid wax is made by adding a heaping teaspoon of alumina hydrate (200 mesh) to a small container of wax resist (pictured below). 
  • I also add a bit of black india ink. The ink is a signal. It makes it easier to see the wax. It also lets me know that this is "lid wax".  Otherwise, I might mistake it for plain wax resist and use it for decoration. Firing removes all traces of ink. I stir it well and repeatedly as I work.
  • On the stoneware I use, I can get by with using plain wax resist on one of the two parts.

  • During firing the wax and ink disappear, but the alumina hydrate leaves a white dust residue. This white refractory dust is what keeps the lid from fusing to the pot.
  • It is fairly easy to wash off the alumina from the finished clay so long as you don't get it on glaze.



    Recipe for Lid Wax

    1. About an inch or two of wax resist in the jar.
    2. Add a teaspoon or so of 200 mesh alumina hydrate.
    3. Add 5 or 10 drops of india ink.
    4. Add a conservative amount of water if needed for brushing consistency.
    5. Shake well before using. Stir frequently while using. Keep the alumina suspended.

List of Hints for Potters
Hint #1:  Potter's Wheel Speed Limit
Hint #2:  Firing Stacks of Greenware Plates
Hint #3:  Setting the cone packs in the kiln.
Hint #4:  Preventing Stuck Lids with Lid Wax
Hint #5:  Preventing Warped & Cracked Tile 
Hint #6:  Preventing Cracked Slab Boxes
For more hints, come back soon.  Your comments are welcome.

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e-mail:  marvinpb@goshen.edu
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