Mark Issenberg sprays fireplace wood ash glazes on pottery

Mark Issenberg sprays fireplace wood ash glazes on pottery

‘Tis the season of ice and snow, so I thought today’s post would be a fitting one since it involves fireplaces.


Mark Issenberg shares some ceramic glaze recipes that utilize fireplace wood ash to create an ash glaze surface. Plus he shares his tips for using a spray gun to apply the glazes. Judging from the brutal winter, fireplace ash should be easy to come by. And, hopefully, you can clean out your fireplaces and not have to fire them up again until next winter! – Jennifer Harnetty, editor.


I started using ash glazes because I liked the idea of utilizing a material that many would consider waste: wood ash from a fireplace. While living in Miami after Hurricane Andrew in 1992, there was an abundance of wood for fires on cool nights, so I had a source of ash. I decided to make ash glazes using 50 parts Redart and 50 parts ash.

Through my experimentation, I learned to use sprayers for applying an ash glaze. To begin, prepare ashes by running them through a flour sifter to remove unburned wood, charcoal and big chunks of debris, then run the dry ash through a 40-mesh screen. I usually process a 5-gallon bucket of ash at one time.

Caution: Wood ash is caustic, so work in a well-ventilated area with a respirator, and wear safety goggles and chemical resistant gloves.

The next step is to weigh equal amounts of ash and Redart clay. I only mix up what I’ll use in one firing (1000 grams of each) since the ash glaze does not store well. After mixing with water, run the glaze through a 40-mesh screen then through an 80-mesh screen to get it to the right consistency for spraying. Use a thinner glaze than you would for dipping or pouring.


 

Want to learn more about wood firing?
Learn the secrets of the masters with Japanese Wood Fired Ceramics,
available in the Ceramic Arts Daily Bookstore.


Due to space limitations, I spray outside, but if you spray inside, you’ll need a spray booth with proper ventilation. I use a portable sprayer and set the compressor at 40 psi. I use a really heavy turntable that turns easily partly because I spray the shaft with lubricant each time I start the glazing process. You’ll also need a gallon bucket with a small sponge for cleaning areas where you don’t want glaze, and a towel to keep your hands dry. With all bisqueware prepared and four to five sprayers ready to go, you can begin the glazing process. Start turning the turntable just before you start spraying. With bowls and platters, start with the bottom and glaze the footring first, then the outside body.

Work with the spray gun about 5-12 inches from the surface and use steady even strokes to avoid getting excess glaze in any one spot where it can drip. Use a sponge to clean the footring. I don’t use wax on bowls because the glaze builds up and runs off the wax, but I do wax flat bottoms. I then flip the bowl and spray the inside using a couple of different glazes. When fired, ash glazes run but some of the other glazes don’t run at all. Testing determines how certain combinations will behave.

Blue Ash Glaze, Cone 10 Light Green Ash Glaze, Cone 10
Glaze Material Percentage Glaze Material Percentage
Ash 50% Ash 50%
Plastic Vitrox Clay (PV Clay) 50 Plastic Vitrox Clay (PV Clay) 50%
Total 100% Total 100%
Add: Cobalt Carbonate 2% Add: Copper Carbonate 3%
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