|Monthly Tech-Tip |
I am looking for patterns in Cooper Red glaze chemistry and not finding any. I pasted some recipes I found on the net into my account at insight-live.com, then exported them as CSV, opened it in Open Office Calc, removed the unneeded rows, transposed it, fiddled with the column and row titles and combined some rows to get this. CaO varies alot, so does KNaO (I expected the latter to be high always). The Al2O3 is all over the map, so is B2O3. Even the copper sees a four-fold difference! Some have or have no ZnO, MgO and Li2O. However SiO2 is always 3.5 or lower and CaO is always above 0.45, while that is at least something of a pattern, most cone 10R glazes have this anyway. It seems that just about any transparent glaze will make a copper red.
The color red is very difficult to achieve in ceramics. The most vibrant red within the reach of the average potter is the color produced by copper in reduction firing.