John Britt Oil Spot Base (modified) ^6 Oxidation
Custer Feldspar 33.5%
Kona F-4 14.34%
Red Iron Oxide 9.78%
J Britt Oil Spot Cover
(Add colorants to this)
Custer Feldspar 30%
Gerstley Borate 30%
White - Add Zircopax 10%
Green - Copper Carb 4%
Blue - Cobalt Carb 2%
Aquamarine - Cobalt+Copper+Chrome 2% each
Brown - Red Iron Oxide 8%
Green - Chrome Oxide 2%
Green - Nickle Oxide 2%
Inclusion Stains at 5%
Both base and cover are mixed with 78 grams of water for every 100 grams of dry mix.
BEST REAL WORLD RESULTS;In production, I HIGHLY recommend that you spray everything. I have found that dipping smaller pieces works, but DIP COVER GLAZE 1 TIME ONLY to prevent the glaze from "fracturing". Leaving the cover glaze at 78 grams water to 100 grams of dry mix yields a very thick glaze. It works great in my sprayer, and creates the spots I want. The thicker the glaze is sprayed, the bigger the spots are. But there is a breaking point in the thickness of the glaze application, so test Test TEST before committing good forms to trying out this glaze!
This glaze will run off the pot when applied thickly at the bottom of a form, so make sure that you glaze a little lighter toward the bottom of the form, trim a good foot when you are creating the work, and fire on stilts. All of my kiln shelves are coated with ITC-100, and I dust aluminum hydrate on the shelf under the pieces that have generous glaze on them. In preparing to load my kiln, I actually use the hot-glue gun to tack the stilts to the bottom of my work. Having the stilts glued on makes it very easy to arrange the work on the shelves with the minimum amount of messing and time spent. Thickness of glaze is critical, base glaze and cover glaze are as close to even as I can get.
I know that a 12"x12"x12" pot needs to have about 28 ounces each of base and cover glaze. Thicker at the top, thinner at the bottom to prevent run off. The only way to figure out the application sweet spot is to just keep messing with it, and taking good notes as to how the raw glaze looks when applied I.e.: spray until the fresh glaze stays wet for a few seconds but does not run. Very fine line!
The bisque piece MUST be bone dry to start and bone-dry between base and cover glaze applications! Apply liner glaze, dry piece to bone dry, apply base glaze and dry to bone dry. Apply cover glaze ONLY to bone dry piece! Applying layers to damp work will cause sloughing of the glazes during firing. If the fully glazed piece develops ANY cracks or fissures in the glaze surface, wash it off and start over with a BONE DRY pot.
Firing Schedule -Top peephole of kiln is left open all the way through firing, including the soak period. Top peephole is closed when soak is completed, when down-firing starts. Leave all peeps closed until completely cooled. This firing schedule is patterned after Ron Roy's standard firing ramps.
Down-firing at 50*F/hour is very important, and will help the glaze smooth out. With a top temperature of 2170*F, the spots are moving, at 2195*, Hares Fur starts to show up, as does serious run off and ruined kiln shelves! SO BE AWARE and VERY CAREFUL of your maximum temperatures!!