Alberta Slip Floating Blue Cone 6
Recipe
Notes
This glaze creates a rich blue yet contains none of the world's most expensive common ceramic material, cobalt oxide. On dark bodies the depth of color is incredible. It has a great glossy surface, and, because it contains no raw metal oxides or stains, toxicity issues are less of a concern. On lighter bodies it variegates from medium steel blue, where it is very thick, to amber clear (or a brown if the body is dark) where thin. The blue color does not develop well on porcelains or white-burning stonewares (unless you underlay it with a dark-colored engobe). This glaze requires a slow-cool firing schedule to work (see the paragraph below). Experiment to get it the right thickness in your circumstances. Try it on different clays and different thicknesses to find the best combination. If it is melting too much or too little, you can increase or decrease the frit to compensate. But don't change the frit without testing first (the blue likely won't develop). Be sure your kiln is actually firing to cone 6 (using self-supporting cones). One possible caution: This glaze relies on the "rutile variegation effect". Rutile can vary in chemistry over time and from place to place, so test this first before using and test it again when you get new supplies of rutile. THE DEEP BLUE EFFECT REQUIRES SLOW-COOLING (otherwise the glaze will just fire an ugly brown). This can happen naturally with fully packed kiln-loads or with well-insulated kilns, otherwise, you must program the cool (use the Slow Cool C6DHSC schedule, it drops the temperature, then holds, then slows the cooling to about 1400F). You can also add 0.25% cobalt oxide to restore the color if you want to do a faster cool (to prevent transparent glazes clouding, for example)! If the blue is working, but less than you want, then add a little less cobalt. If the glaze shrinks and cracks too much on drying, then increase the roasted Alberta Slip and reduce the raw Alberta Slip. If it is too powdery on drying, increase the raw against the roast. There is also a Ravenscrag Slip version of this glaze, it employs iron, cobalt and rutile (like the original David Shaner recipe).
Description
Plainsman Cone 6 Alberta Slip based glaze the fires bright blue but with zero cobalt.