Tuesday, October 16, 2012

October 15th Hint of the Week

from the Goshen College Art Department http://www.goshen.edu/art/DeptPgs/ArtDHome.htm

by Marvin Bartel http://people.goshen.edu/~marvinpb/MB_Home.htm

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…lid wax.
Making Lid Wax
Lid wax is made by adding…alumina hydrate…to a small [amount] of wax resist. You may also add a little water to get it too brushing consistency. [Generally you should only be mixing enough lid wax for your project. It takes only a small amount and we don’t make up large batches. However if you make more than you can use please mark any leftover lid wax, and put it in a small container on the shelf in glazing room, as this is community property].
I also add a bit of black india ink. [Ink is optional] The ink is a signal. It makes it easier to see the wax. It also lets me know that this is "lid wax" [please mark any leftover lid wax, if not we’ll have to throw it away if unmarked]. Otherwise, [someone] might mistake it [lid wax] 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.

No comments:

Post a Comment