What the Flux!

(February 2023 Edition)

It’s all about the Blues. In October, TPS added many new glazes to the collection and two of those glazes were Sapphire Blue and Rusty Blue – two very different blues that interact beautifully with the range of clay bodies available at the Studio. If you have not yet tried them out please indulge in the blue journey and develop some interesting combinations for yourself. These two blues are different from combinations created by clear and teal or however you were previously able to develop a blue from our old glazes. Combined with other glazes are all on their own these two blue glazes look lovely on dark and light clay bodies.

Understanding glaze chemistry is foreign to many of us, but fortunately, thanks to Bill Kaplan’s assistance, we can share this basic understanding of the chemical elements and how they come together to bring life and color to our pieces. The chemicals in a basic glaze form a glass, they stabilize the glass and cause the glass to melt at a lower temperature. The molecular formula or the UMF puts the chemicals into certain proportions and the proportions determine how the glaze will behave. The main glass former is silica (SiO2) and it melts at 3100 degrees F or Cone 32! The stabilizer is alumina (Al2O3)and that is what keeps the glaze from completely sliding off the pot and then there is the flux, which allows the silica and alumina to melt at lower temperatures. There are two groups of fluxes, feldspars and carbonates. Both are needed and the proper balance is critical. Bill is the master of getting the right balance of the UMF. This portion of the newsletter will introduce, discuss and explain a little bit about the TPS glazes. First up, “the Blues.”

Rusty Blue is based on a 50-year-old recipe from the 70s. The glaze materials used have changed somewhat from when Rusty Blue was originally created. It was originally more purple. The copper blue that is one of the primary ingredients will reveal more red iron rust when applied thinly or on an iron bearing clay. When Bill originally developed this latest recipe, it was a bit runny, so of course he added silica and alumina to help stabilize the glaze by raising the melt temperature.

Rusty Blue has a wide variety of color depending on the clay body which adds another element of chemistry, especially if it is a clay body that has a lot of iron. Changing the chemistry of the melt will push the red iron oxide in the clay which will manifest differently based on the clay body. However, when applied to porcelain you will see the true blue color. Also depending on how the glaze is fired from heavy reduction to no reduction there will be a wide range of color. When combined with other glazes, Rusty Blue can be more inert. By carefully putting another glaze over Rusty Blue or under it you can push the glaze to even more colorful dimensions. What have you found to be the most fascinating combinations with Rusty Blue?

One fun and unexpected outcome is yellow salt on Rusty Blue dipped for 2-4 seconds. The glaze will break apart like confetti. A combo of red and shiny white also reacts differently and over reduction will produce more red because of the titanium that is in the glaze. So go out and experiment on test tiles with clay bodies and others glazes and when you do apply the glazes to your pieces, please, please, please don’t forget your cookies.

Sapphire Blue has a base of cobalt and copper. There is some titanium in the glaze that will make it go green when added with other glazes or if applied thinly. If thickly applied, the blue will become more predominant. Sapphire Blue doesn’t break the same as Rusty Blue; however, you will see more variation on lighter clay. By itself, Sapphire Blue is a lovely blue with spots of light blue. Before you combine it with other glazes, experiment with using only Sapphire Blue on different clay bodies and for varying dipping times to see how much the glaze transforms. When you do decide to combine with other glazes start with Sapphire Blue only on the top 25 percent of your piece and then see how it mingles with other glazes. Several things will emerge at once, a thin application will be green and a thick application will be more blue.

Now get down to the Studio and let’s see you work through the Blues.

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