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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.
FredoniaLime^10R1200px.JPG
This set shows some typical features of high calcium glazes. In the bottom left quarter (high in fluxes) the glazes are quite runny in this stoneware reduction firing. They exhibit many of the characteristics of wood-ash glazes (also high-calcium), including the rivulets of glaze on a vertical surface called webbing or stringing. The top left quarter (high alumina) glazes show a tendency towards colour-break, breaking to the brownish colour where the glazes are applied thinly. This type of high calcium alumina matt has been exploited for decades in a range of colour-break glazes, especially with colourants iron (earthy red breaking to yellow) and cobalt (blue breaking to yellow). The bottom right quarter (high silica) shows some typical high silica effects: opaque glazes and opalescent blue glazes. The crystals in glaze number 34 seem to be typical of some high calcium glazes; the effect requires low alumina and the right amount of silica.
Lichen^6ox1200px.JPG
Showing the effect of a high percentage of light magnesium carbonate in the grid. One can use 40 or 50 % of light magnesium carbonate in the C-corner, with the balance of the fluxes being frit for mid-fire or nepheline syenite for high-fire. Add other fluxes and additives like colouring oxides and rutile if you wish.
ParksvilleFCX2^7ox1200px.JPG
This set uses a fairly normal set of fluxes for mid-fire with the addition of titanium dioxide to all the recipes giving a preponderance of opaque glazes. The little crystals are from MgO in the flux set.
Dol/Sr/Zn^10R_Tuscany.JPG
Dol/Sr/Zn^10R_Tuscany.JPG - Grid Tile fired at La Meridiana at the workshop in 2005
Ba/SrComparison1200px.JPG
Comparison of two grid tiles, identical in all ways except for the substitution (in the right-hand tile) of Strontium carbonate for Barium carbonate, weight for weight. Clay body and firing are identical.
Haarlem'06BaBl^3&^9ox1200px.JPG
Comparison of two grid tiles with identical sets of high barium glazes showing the temperature stability of barium matt glazes, Orton cone 3 on the left and Ortone cone 9 on the right, both fired in oxidation.
Brantford Chrome/Tin Red
Deconstructing Ron and John's Raspberry Glaze. It can be quite interesting on dark clay. The variation of alumina and silica provided by the grid allows one to choose the most interesting combination for your materials, clay and firing. It is obvious from the tile that these reds do not like high alumina. This tile fired to Seger cone 7 (about Orton cone 8) in oxidation at the Heide workshop in Germany, 2008.
