NFU Crystalline Glaze

Zinc Silicate Crystalline Glaze Pottery

A chronicle of my recent progress and a way for me to keep it straight in my head!

 

Formula

51.8    Ferro 3110

24.5    Zinc Oxide

14.4    Silica

1.2    Kaolin

4 Rutile

3 Red Copper Oxide

4 CMC

 

glaze with 4% CMC and thick shake consistency.

 

 

 

 

 

 

Glaze Thickness

I've been seeing many pieces where super thin glaze grew 5X+ faster at the lower temperatures than normal.

The pot below has broadly separated rings on its top which formed at temperatures below 1000C. And on the shoulder where it is thicker, and the high temperature crystals (1050C to 1080C) grow quickly there is little separation between the low temperature bands.

 

 

I used essentially the same schedule as April 22nd, holding down as low as 860C. It seems the thickness of this glaze at these low temperatures has a major impact on whether these crystals will form and grow. The photo below shows the number of firings and glaze application rate. Notice the amount of glaze in the catchers.

 

 

 

1, 2, 3, 4 and 5 coats of NFU. I think this test demonstrates that a thin glaze layer is key to the formation and growth of crystals at these low temperatures.

 

 

Too thick

NFU except 1, 1 3/4, 2 1/2, 3 1/4 and 4% rutile. Things seem to be on target with the 4% rutile currently in NFU.

 

 

made with .30 g/sq.in. glaze  loading

 

 

.25 -.30 g/sq.in. glaze on bottom, .6 - .7 g/sq.in. on top?

 

These were all controlled at 0.4 grams (dry) per square inch

 

 

The background color and shape of the brown crystals change significantly with glaze thickness.

 

 

 

 

This piece has a glaze loading of ~ .40 g/sq.in.,

 

 

They had 0.51 and 0.46 g solids / sq. in. of surface

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Phil Hamling

376 County Route 1

Warwick, NY, USA 10990

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