The chip of this glaze on the manufacturer’s fired results board has intrigued me for some time. It’s a beautiful shade of blue, with just a hint of a metallic sheen. Several times, I’ve pulled this glaze from the shelf to use in a Second Saturday Raku Firing, but because of all the other glazes out on the table for participants to choose from, I never was able to really see what this glaze does. Being curious (some might even say slightly obsessive), I wanted to get to know this glaze and learn more about it. So, I did a full kiln load of nothing but Cobalt Blue….I used thrown pots, handbuilt pots, textured pots, smooth pots, pots with one coat of glaze, with two coats, with three coats, reduced in sawdust, reduced in excelsior, and even just oxidized. The results were fantastic. Most notable to me is that where the glaze was most heavily reduced, the metallics in the glaze really came out, producing a beautiful bronze/copper with some iridescence around the edges. The sawdust most often produced this effect, clinging to the glaze and causing heavy localized reduction, whereas the excelsior provided a much more stable reduction atmosphere in the chamber as a whole, giving more general results.
(NOTE:Excelsior is wood shavings usually resulting from the use of a lathe. I get it from Uline, who sells it as packing material)
I also loved that when the glaze was thinner, it was almost a silvery iridescent lustre-y blue with the softest flashes of periwinkle. Definitely more fun to be had with this glaze.
Bracker’s stocks Spectrum’s Cobalt Blue Raku Glaze in 4oz jars, and the retail price is $5.00