Wiseman Ceramics

The basic goal with a zinc-silicate crystalline glaze is to create a completely melted solute of Zinc and Silica. This is achieved through flux and heatwork. If one goes down, then the other must go up to compensate; however I do not believe that flux can be directly used as a replacement for heatwork when going after the effects of ^9+ crystalline glazes. You’ll see what I mean when you look at the visual produced at cone 6.
That is not to say that ^6 isn’t a worthwhile endeavor… My feeling is that crystallines produced at lower temperatures should be viewed as an aesthetic all their own.

During the past 2 years, I have been firing within the ^11-12 range. When I first started however, I was limited by the school kiln that would not satisfactorily fire above ^8. I actually ended up firing in the ^6 range, but the experience I gained in the ^7-8 range provided just enough heatwork to get the glaze to look more like the higher fired versions. So if the kiln you have access to can be fired that high, it’s worth exploring.

William Schran’s crystalline glaze testing in the ^6 range is extensive, which is why he was invited to present at LatticeStructures™ 2005 on this subject. His main addition to the glaze as an auxiliary flux is lithium carbonate. I would also suggest experimenting with additions of sodium, as this is one of the most powerful fluxes. Boron is stronger, but most people agree that it can disrupt macro-crystal formation… that being said, try small percentages anyway. To add sodium, try Nepheline Syenite or Kona F-4 Feldspar. Sodium Carbonate can be used as well, but keep in mind that it is a water soluble chemical.
Lithium may have been chosen as it doesn’t encourage the crazing as much as sodium, but there is so little of either that needs to be added to decrease the cone value that it may not matter. Lithium is said to promote brighter colors and encourage crystal growth (the latter is documented only at low-fire temperatures, however).
Schran would have more experience here.

The most valuable information I can offer for anyone attempting to learn an aspect of glaze chemistry is to concentrate on each ingredient. Refer to the post: “Getting Started with Crystalline Glazes“. Here the main focus is flux, zinc, and silica. Endeavors to fire to ^6 are already going to adjust the first, but one would benefit greatly by taking all three components and creating a small 10 cell triaxial or quadraxial graph. Knowing what each part of your glaze base does in greater and lesser amounts, and having a visual record in the form of tests, will help immeasurably in the future.

A basic recipe for a ^9-10 crystalline glaze is >
Ferro Frit 3110: 50%
Calcined Zinc Oxide: 25%
325mesh Silica: 25%

2 good starting points for ^6 are >
1- Ferro Frit 3110: 58%
Calcined Zinc Oxide: 21%
325mesh Silica: 21%

2- Ferro Frit 3110: 50%
Calcined Zinc Oxide: 25%
325mesh Silica: 25%
Add:
Lithium Carbonate: 5%

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Links To Explore:

“Reducing the Firing Temperature of a Glaze From Cone 10 to 6”
by Tony Hansen