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Mid Fire Glazes
Grid sets that contain glazes suitable for mid fire.
These sets contain glazes that are suitable for around 1200 deg C. or around cone 5... plus or minus 50 deg C at least, or a couple of cones. Many of the glazes on these tiles will be better at higher or lower firings, to be determined by the experimenter. Although there is usually a best firing range for a particular glaze, there is no best temperature for any grid tile; any grid may be fired over a range of at least 100 deg. C, and at different temperatures, different glazes will reach their best result.
Iron/Bone Ash Red Set
Fired to Orton cone 10 in oxidation at the workshop at Keramikos in Haarlem, Netherlands, 2008. This set shows how the combination of iron oxide and bone ash can make some rich iron-red colours, with interesting small crystal development in many of the glazes.
HaarlemCrSnRed^Comparison
Temperature comparison from cone 4 to cone 10 showing some chrome/tin red glazes. At the firing temperature rises, the high alumina glazes (across the top of the tiles) lose the red colour from the chrome/tin combination.
LA-CoTi^7+ox1200px.JPG
A combination of cobalt and titanium produces matt greens with the right amount of alumina in the glaze. For high-firing, this green can be obtained by putting cobalt and titanium (often as rutile) into a shino-type high feldspar (or nepheline syenite) glaze. To get it to mature at mid-fire we can add frit to the set of fluxes and additives, and construct a grid to find where it occurs at the lower temperature. To go from stoneware (e.g. ^ 9 or 10) down to mid-fire (e.g. ^ 5 or 6) firstly enter the original flux and additive set (names and amounts) into the Calculation Page. Now add frit to the flux set and by trial and error, recalculating each time, find what number you need to enter in Row 2 to give 30% frit in the corner C glaze (glaze 31) on the resulting recipe sheet ("35 Recipes for the Set"). You then produce a grid from the corner glazes provided where it says: "Corner Glaze Calculation - Batch Recipes for Volumetric Blending". Once the set is fired it will show where the green occurs with the new set of fluxes. Different frits will give different results; the frit lowers the maturing point for all the glazes in the set by brute force.
