Crystalline Glaze with Nickel Blue
I opened the kiln a couple of days ago and was delighted to see these glaze tests smiling back at me! It was especially good to see them as almost nothing else had worked as it should in that firing, so the little tests were needed to give me the encouragement to keep going!
These are tests of crystalline glazes with a little Nickel oxide added to colour them. Nickel can behave in a very interesting way in crystalline glazes in that it can give two colours from the one metal. The crystals are likely to be blue, and the surrounding glaze could be yellow, orange, or green!
The two glaze tests on the left of this photo were the same glaze recipe fired at different temperature. It is amazing to see the transformation that a mere 55 Celsius (131 F) has made! The first test (from an earlier firing) was fired at cone 7 (approximately 1230 Celsius (2246 F)) this has given a satin matt glaze; the second test was fired at cone 10 (approximately 1285 Celsius (2345 F)), and has dramatically changed to a shiny glaze with large crystals.
For those who might be interested, here are the glaze recipes used....
From the left, tests 1 and 2
use a Janet DeBoos Recipe (number 84 in her second book of glazes)
Potash Feldspar 35
Zinc oxide 24
China Clay 5
+1.5 Nickel oxide
The three other tests use my base (which is slowly evolving)
Fritt 4110 (3110 in some countries) 47
Zinc oxide 27
China Clay 0.5
Test 3 (The center test) has + 2 Nickel oxide
Test 4 has + 1 Nickel oxide
Test 5 has + 1 Nickel oxide, 4 Manganese dioxide.
I fired this kiln manually and used cones for top temperature.
The firing took about 9.5 hours to cone 10
40 minutes to fall to about 1100 C (2012 F)
Hold for 4 hours.
Note: I made several changes to the hold temperature to encourage growth rings to form in the crystals. I find a sudden drop of about 40 C (104F) from the holding temperature, a 5 minute hold, then a quick rise to the original holding temperature gives nice growth rings.