In the Studio: In the Glaze Kitchen Dan Ingersoll

Appears in the May/Jun 2020 issue of Pottery Making Illustrated.

Twenty years ago I promised my wife that I would make us a new dinnerware set. I finally made good on the promise and got it done! Well, not totally done. The set has been made for over a year, just waiting for me to figure out how to glaze it!

For this set, I needed to find a cone-6 oxidation glaze that was aesthetically pleasing and met the criteria of being appropriate for food use, durable, and resistant to utensil marking. My client (my wife) requested a simple palette of black and white. I normally high fire in a wood kiln and have had little experience with functional, cone-6 electric glazes, so this posed a challenge.

Beginning Research and Testing

The road to find a glaze led me to the Facebook group Ceramic Recipes/Formulas (www.facebook.com/groups/disisdkat); the Glazy website (https://glazy.org); Tony Hansen’s site Digitalfire (https://digitalfire.com/index.php); and John Britt’s book, Mid-Range Glazes. Additionally, I found a deal on Craigslist for a digital test kiln. The kiln, along with the resources listed above, opened up a whole new world of glaze experimentation and testing options.

After much testing, I settled on using Tony Hansen’s G2934 as my base glaze (see 6). This glaze is matte when slow cooled and a nice, durable satin finish when cooled naturally. It met all my criteria for a functional dinnerware set, and as an added bonus, it is easy to remix even after sitting for long periods of time.

Finding the Color Palette

This base by itself doesn’t show utensil marking; however, when I added 10% Zircopax to achieve a strong, silky white, it created a bright white surface that marked badly. When I cut the Zircopax to 5%, I still achieved a nice white glaze over a light clay body, and the very light utensil marking that occurred washed off with ease.

For a silky black glaze, I experimented with additions of Mason stain 6666, Mason stain 6600, and red iron oxide (see 4). Adding 6% of red iron oxide to the base glaze resulted in a rich, dark brown/black. Adding 6% of Mason stain 6666 resulted in a medium brown. Adding 6% of Mason Stain 6600 yielded a silky black. I also tested the addition of 6% red iron oxide and 2% Mason stain 6600, which created a soft black.

When testing the layering of the various black and brown glazes with the white glaze to see how they played together, I very quickly learned a glaze application that is too heavy results in bad crawling (1). To avoid this, it’s important to keep the specific gravity around 1.45 to prevent a heavy glaze buildup on the second dip. With a single dip, you can dunk your pot and hold for three seconds to get a smooth, finished surface. When layering, the first dip must be quick, followed by a second quick dip as soon the first has dried enough to handle. When the white base was layered over the black/brown glazes, some very exciting breakthrough and spotting occurred in the fired glaze surface (see 5).

While testing the G2934 base glaze, I also tested some cone-6, iron-red glazes. I surmised it was the addition of iron that accounted for the breakthrough effect in the glaze combination in my earlier test tiles, so I tested the iron glazes with the G2934 base on top. The most pleasing result was from an iron glaze called Sankey Red, originally sourced from John Sankey (see 6). Before going all in on the dinnerware set, I began experimenting with glaze combinations on rice bowls with wax-resist design. Sankey Red was used on the three noodle bowls (see 3).

After many trials, I finally settled on a glazing design for the dinnerware set using G2394 + 5% Zircopax in combination with G2394 + 6% red iron oxide and 2% Mason Stain 6600. The glazes were sprayed rather than dipped and the result was a more subtle breakthrough of the black glaze with fewer defined spots (2).

 John Sankey recipe link: https://johnsankey.ca/glazeiron.html.

Final Thoughts

I’ve always been a bit intimidated by the chemistry and creation of glaze formulas. What I found was that the Internet is rich with resources ready to be mined, and a test kiln opens the door to many possibilities and is worth the investment.

Dan Ingersoll taught for 35 years as a public-school art teacher, 17 of them teaching high-school ceramics, and continues to pursue his passion for clay and sculpture in his retirement.