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Casting Jiggering

The slip-casting process is well adapted for producing non-functional ware, especially having thinner walls. However it does not do well for functional pieces that require thicker walls and contoured lips (heavier cast walls have less regular wall thickness). However these issues can be dealt with by adding a jiggering step to even out the wall and round and contour the lip.

For the jiggering step to work a casting slip of adequate plasticity is needed so that clay does not tear when subjected to pressure from the template (more plastic slips need more ball clay and less kaolin, this can mean that longer casting times must be tolerated).

To jigger the lip of a piece it has to be cast in such a way that the clay extends upward from the top of the mold. The key to achieving this is 3D-printing a pour spout that and carefully placing and gluing it to the top of the mold (using slip). After draining the molds, the spout can be removed and the jiggering process done.

There are a number of complications to effectively creating this process in a studio, but with the advent of 3D printing many of these have been removed.

An interesting aspect of this process is that "weekend warrior" potters can employ it to produce ware. Within a two or three hour time window molds can be filled, poured, jiggered and pieces extracted ready for handle attachment and drying. Since these bodies normal shrink very little, drying can be done without any need for covering ware.

Hand-tooled jigger model vs. 3D-printed and cast

Hand-tooled jigger model vs. 3D-printed and cast

I am creating molds for a casting jiggering process to make mugs. I have a profile drawing I want to match (upper left). The solid model on the left is my first attempt at manual tooling. The metal template was time-consuming to make by hand, it worked poorly (the surface is rough). And the contour matches the drawing poorly. I lost the enthusiasm to even get it smooth. For the one on the right I 3D-printed a shell, poured the plaster in and then smoothed it off a bit on the wheel after the set. It matches the template and it is perfectly round (because I have a good 3D printer, a Prusa MK3S). This is revolutionary! That drawing: I hired someone on Upwork.com to draw it for me using Fusion 360. He draws things in such a way that I can fine-tune them. Then I print them using my own 3D slicer.

A gunmetal glaze I have wanted my whole life!

A gunmetal glaze I have wanted my whole life!

After 40+ years of making pottery I finally have a perfect gunmetal black. It has an incredible silky glaze. It does not cutlery mark. It does not craze on anything. It is easy to clean. This is G2934Y with 6% Mason 6600 black stain. I had to tune it a bit, adding about 10% glossy G2926B, because it was a little too matte on the first firing. But now its perfect. These are heavy mugs made using the M340 casting recipe (and the casting jiggering process). The speckled mug was made by casting a thin layer of the speckled version of the slip first, then filling the mold with the regular slip. I used a 40-minute cast to get walls nice and thick!

Out Bound Links

  • (Glossary) Jiggering

    A process for mass-producing simple shapes on a mechanized pottery wheel having a solid swing-arm with a template. For plates, a profile describing the outside shape of the ware is used to force the soft clay against a rotating plaster mold describing the inside shape. For vessel forms, the profile ...

By Tony Hansen

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