Low-Fire pottery: Bright underglazes, transparency, fired stability

You can decorate the underside! The one on the right is the back side of the plate. This is Plainsman Snow clay, it has 25% absorption at cone 06-04, this level of porosity is so high that the body can actually absorb the molten glaze if it is melt-fluid enough. However, when fired at cone 06 the body does not absorb any of the glaze. And the plates stay flat when fired on stilts. These are done by the team of Micah & Jeremiah Wassink of Creston, BC (at Pridham Studio). They make matching mugs, but fire those at cone 6 using underglaze decoration with a clear overglaze. But these plates are decorated using a combination of heavily pigmented viscous-melt low-fire glazes and a black underglaze and then finished with a thin layer of transparent glaze. Since the glaze is not crazed, water is not able to penetrate into the body. And the layer of clear glaze isolates the heavily pigmented colors from food. Even though they are low fire, these pieces are functional and food safe.

Related Pictures

The right transparent glaze makes this underglaze design shine!

A cone 6 plate with underglaze fish design

The underglaze decoration on this cone 6 porcelain plate, by Dana Powell @danaspottery, is undeniably impressive. Many who struggle to find a glaze that is adequately transparent and does not bleed edges at cone 6 would find this clear overglaze even more amazing. A lot of work goes into a design like this, not surprisingly many potters prefer cone 04-06 for this type of work. At cone 6, reliable transparency requires a recipe and temperature that achieve just enough melting to get a smooth and glossy surface but not so much that the underglaze dissolves (a slow-cool firing schedule makes it even better). And of course, it must not craze. But most important is a predictable and consistent glaze thickness over both the body and underglaze. This can be tricky using a dipping glaze, they tend to go on too thick on the porcelain and don't stick well to underglazes (the best chance is with a thixotropic slurry). Mixing the recipe as a brushing glaze or using a commercial brushing product could also work, a best-case scenario is the pour brush glazing technique. However, brush action could also smear the underglaze. Mixing your recipe as base-coat dipping glaze could be the best answer. The right amount of gum (you will have to experiment) will drain fast enough to dry in a minute or so and spread out evenly into a thin and dense laydown that adheres equally to body and underglaze. Of course, you would need to hold the plate (or hang it somehow) on edge while it drips.

Links

URLs	https://www.pridhamstudio.ca/ Pottery in Creston, BC, Micah and Jeremiah Wassink
Glossary	Transparent Glazes Every glossy ceramic glaze is actually a base transparent with added opacifiers and colorants. So understand how to make a good transparent, then build other glazes on it.
Glossary	Underglaze An intensely pigmented highly opaque non-melting ceramic material mix meant to adhere best to leather hard pottery and fire-fit the body. Often transparently overglazed. Starter recipes.

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