CRYSTALLINE GLAZE & PORCELAIN POTTERY RESOURCE


SPIRAL


 STUDIO

Introducing: "WILD STYLE"

An exploration into the effects of temperature on crystal shape.

Please click on any photo to enlarge.
1): Salad plate, 7-3/4 x 8", $45.
2): Butter dish, 7-1/4 x 5-1/2", 34. sold
3): Sushi server, 5-1/2 x 4-1/2", $29.
These pieces were fired to a peak of 1255C. The kiln was then allowed to "naturally" cool to 1110C, and was held there for four hours. The kiln was then allowed to cool naturally to room temperature. It should be noted that I have a large, super-insulated kiln with a very large heat mass. This means that when I allow it to cool "naturally," as opposed to forced cooling, that it does so slowly.

It is well known among crystalliers that there is a definite temperature window in which zinc-silicate macro crystals can be grown. Above this temperature, the crystals dissolve, and the artist is left with "nothing." Below this window, the molten glaze is no longer fluid enough to allow the molecular movement required for crystal growth.
It is also well known that at the lower end of the crystal-growing temperature window, nice, perfectly round crystals are created. And, at the upper end of the window very thin needle-shaped crystals are grown. In between these extremes, fan-shapes, axe-heads, German crosses and "spiky" crystals are created.
I began my exploration into crystal shapes by trying to define what the upper end of my temperature window is. I also wanted to see just how thin a needle crystal I could make. My first attempts are shown above. These crystals were grown at a temperature of 1110C (1110 degrees centigrade), which I have determined through experimentation, is just about the reasonable maximum growing temperature for my glaze. Above this temperature the crystals would grow too slowly. Of course, the peak temperature and the crystal-growing temperature window is going to be different for each glaze recipe.
The "fuzzy" white edges on the above crystals are halos that grew after the kiln was turned off and the work allowed to cool naturally.

4): Saucer with gold lustre rim, 4-3/4 x 5",
$30. Fired in bottom of kiln.
5): Dinner plate, 10 x 9-1/4", $40.
Fired in middle of kiln.
6): Sushi server, 5-1/4 x 4-3/8", $29.
Fired in top of kiln.
As before, these pieces were fired to a peak of 1255C; the kiln was then allowed to "naturally" cool to 1110C, and was held there for four hours. The kiln was then crash-cooled to room temperature. I crash-cool by lifting the entire lid up 6" (my lid is suspended on a wire and pulley rather than being hinged).

For my next firing, I kept everything exactly the same, except that after the four-hour crystal-growing hold segment I immediately crash-cooled the kiln to room temperature. The kiln cooled so rapidly that there was never a chance for the halos to grow and make the crystal edges fuzzy. The sushi server, above right, has the finest, sharpest needle crystals I have ever created. The needles are literally the diameter of a human hair.
The needle crystals of the other two pieces above are not quite as sharp because they were lower in the kiln, where it took a little longer for the room air to reach and freeze them. Thus, they had time to grow just a hint of a fuzzy, white-edged halo.
The only difference between #3 and # 6 is that #6 was crash-cooled. The only difference between #1 and #4 is that #4 was crash-cooled. (Numbers 4 and 6 were also struck which altered their colors, but this in no way affected their crystal shapes.)

Until now, all of my crystal growing was being done at the high end of the crystal-growing temperature window. For my next firing, I added some crystal-growing work at the low end of the window.

7): Wavy-edge dinner plate, 9 x 10-1/2", $95. sold

I kept everything the same as before, except that at the end of the four-hour 1110C soak, I crash cooled not to room temperature, but to 970C, after which I re-closed the kiln and held the temperature there for ten minutes. I consider 970C to be about the extreme lowest practical crystal-growing temperature for these recipes.
This drop and hold can be thought of as a momentary "freezing" of the glaze. The freeze created many new nuclei, and explains why #7 has the many small crystals not seen in the previous examples.
After the low-end hold, I added the following ramp-and-hold segments in order to grow the new crystals that I had just nucleated larger, and to give them growth rings:

Rate, degrees per hour
Target Temperature
Hold Time, minutes
100
1040
10
100
1000
10
100
1040
10
100
1000
10
How straight needle crystals appear
to fan out or "curve."

As was shown in #6, thin needle shapes are created at the upper end of the crystal-growing temperature window. When the temperature is lowered, new needles begin to grow, at an angle, right out of the sides of already existing needle crystals. Given a chance, the process repeats itself indefinitely. The result is a crystal that appears to bend, or curve or fan-out. In actuality, all zinc-silicate macro crystals are needle crystals. We all typically think of a nice, perfectly round glaze crystal as a single crystal, when in actuality, it is composed of thousands of individual needle crystals.
The lower the temperature, the greater the bend or curve.

In the detail photo of piece #7, you see a large starburst of long needle crystals, which "filled in" and "fanned out" when the temperature was lowered and held. The only difference between #7 and #5 is the added lower-temperature growth segments shown in the table above.

8): Sushi server with gold lustre
rim, 4-1/2 x 5-1/2", $30.
9): Sushi server,
4-1/2 x 5-1/4", $29. sold
These pieces were in the same firing as #7, but they were on the top shelf of the kiln, where they received the greatest exposure to the crash-cooling. Although I say above that I crash-cooled to 970C, these pieces were actually exposed to a temperature of about 850C for about five minutes. That's cold!

Just how low can a crystalline glaze be taken to before it stops growing? The two sushi servers above were momentarily taken down to 850C. At this extreme low end of the crystal-growing temperature window the crystals become 3-dimensional, texturing the glaze surface and causing it to go matte. The second photo of piece #9 illustrates this.
To take this picture, I leaned the dish back and placed a light source behind it, which I reflected off of the glaze surface toward the camera lens. You are looking at a picture of the resulting glare (there is so much contrast from the bright glare that the photo appears colorless). Both glossy smooth areas and textured matte areas are visible.

10): Dessert plate, 7 x 7-3/4", $48.
11): Hors D'oeuvre plate, 7-1/4 x 5-5/8", $39. sold
12): Large dinner plate, 10 x 10", $100.
These pieces were fired identically to #7, #8, and #9, except that I decreased the high end hold from 1110C to 1100C. This was just enough of a change to make the big, initial crystals fuller and less starburst like.
These are amazing pieces. You MUST click on the photos, especially the details, to enlarge them so that they may be fully appreciated.

Take a good look at the enlarged detail photo of dish #11. Like #8 and #9, this hors d'oeuvre plate was on the top shelf of the kiln where it received the maximum effects of the crash cooling. The branching needle crystals have bent or curved (as previously illustrated) so quickly, that they appear to be growing at right angles to the initial spiky needles! This is pretty amazing!
If one looks at the enlarged detail photo of #10, you can see that as the background needles grew, they wove over and under each other 3-dimensionally in the glaze layer. This too is amazing.
Plate #12 was lower in the kiln where it was more protected from the freezing effects of the crash cooling. Thus, the crystal patterns don't exhibit quite the craziness of #10 and #11.

13): Saucer, 4-3/4 x 4-3/4", $32. sold
14): Salad Plate, 7-3/4 x 8", $50. sold
15): Wavy edge platter, 10 x 11", $125. sold
These pieces were fired similarly to #10, #11, and #12 with just a few minor changes.

It was very hard for me to choose which details to photograph. Something new and fascinating is happening on each individual square inch of these pieces. The crystals are just amazing in person, with incredible depth, detail and luminosity. I guarantee that you will find them as spellbinding as I do.