When I was just starting out in ceramics, I thought that getting a disappointing pot out of the kiln was just something a potter had to live with. It never occurred to me that I could try putting it back in the kiln, so my mind was blown a few years later when I learned that refiring pottery was an option. And I have saved more than a few lackluster pots since then.
But refiring pottery does not only have to be reserved for bad pots. It can be worked into the creative process. Justin Rothshank uses refiring to add layers of gorgeous details on his low-fire-soda pots. In today’s post, an excerpt from his new book Low-Fire Soda, Justin gives tips for refiring pottery with added underglazes, glazes, and decals. Of course, refiring ceramics comes with certain risks, but Justin’s tips will help you avoid disasters! – Jennifer Poellot Harnetty, editor.
Refiring Pottery for Enhanced Surfaces!
I have occasionally chosen to refire a selection of my works as another finishing approach to consider. There are several reasons why I may select a piece to be refired:
- To fix a poor glaze result. This might include underfired glazes, a lack of exciting soda surface effects, a faulty wadding mark, or a glaze fault such as pinholing.
- To add a ceramic decal. A finished piece, with beautiful glaze results, may still benefit from additional layers of decoration including decals, china paints, or lusters. Multiple refirings may occur to build up layers of decoration, firing the hottest material first. Background imagery should be fired first, with the foreground imagery being the final firing.
When preparing a piece to be fired again, the already glossy glaze-fired surface can be difficult to reglaze. The glossy surface means liquid glaze wants to drip off the surface. Thickening your glaze—by air drying or adding products like Apt-II or CMC gum—can make this process easier. Preheating the pot will also aid in quickly drying the newly reglazed surface. I have also experienced success when I’ve sprayed a thin layer of glaze over a pot chosen for refiring, specifically highlighting and glazing certain areas that may benefit from a thicker application.
When refiring pots that have a particularly dry surface after soda firing, I’ve also used new layers of underglaze to add color. Spraying, painting, dipping, or pouring the underglaze are all effective methods of application in this scenario, just like when adding underglaze to an unfired surface.
Refiring ceramic wares at any time can cause them to dunt, or break. This can happen for several reasons. First, it is important to be sure that there is no water in the pot—on its surface or absorbed into the piece. When this added water turns into steam, it can cause the piece to crack apart, resulting in a broken piece. This is relatively easy to control. Be sure your pot has dried thoroughly after reglazing it, and then ramp your kiln slowly through water’s boiling point, 212°F (100°C).
The second cause of dunting is if too much cristobalite forms in the clay. Most of this formation happens above 1000°F (538°C) during quartz inversion. This cristobalite form of silica then inverts during the cooling process mostly between 400–500°F (204–260°C).¹ Thus it is important to cool slowly through these temperatures.
Here are a few hints to help avoid cracking, dunting, or other refiring mishaps:
- Be sure your piece is completely dry.
- Fire slowly up to 500°F (260°C), and again through 1000°F (538°C). Cool slowly through those same temperatures.
- Be sure your piece fires evenly so that one side doesn’t get hotter than the other. Don’t place it close to the kiln elements, elevate it above the kiln shelf for even heating, and place it in the most well-insulated part of your kiln.
- Consider using stilts, wadding, or soft brick to protect the bottom of your piece from sticking to the kiln shelf. This will also enable consistent and even reheating and cooling during the refire process.
¹Tony Hansen, “Quartz Inversion,” DigitalFire, accessed December 10, 2019, https://digitalfire.com/4sight/glossary/glossary_quartz_inversion.html.