This was my first batch of ?home made glaze? test tiles ,and all were more or less as anticipated, except for one group.
I was trying to make a glaze based on RR?s Raspberry Glaze but using the ingredients I had to hand. Partly to try out Insight, partly to see what happened.
I was not expecting what did happen: the glaze had literally fallen off the vertical test tiles in sheets ? as if it had at some stage formed a ?skin? but then crazed and crackled like mad. No sign of flowing or running particularly, just as if it had never bonded with the clay surface, and at some stage fractured spit and spattered itself around but none of the spatters had stuck to the bat washed shelf or other tiles. Where it had 'folded off' the tile in sheets, it still rtained an imprssion of the textyure of the time on the sde of the glaze that had been on the tile. Weird.
The kiln was over-fired to Cone 8 (I?m having a real problem calibrating my controller: with a 60C/hr rise I fired to 1205C, and still got Cone 8, should have been Cone 6). Electric, Oxidation, on a buff stoneware body.
Here?s what I ended up with compared to what I was matching with (which may or may not be what the original glaze was, because I don?t know if the Insight database for the demo version would have the same material composition as the RR original).
My recipe: What I was aiming for:
20.78 Whiting 20.00 Whiting 27.09 SILICA 30.00 Silica 7.02 Colemanite 18.00 Nepheline Syenite 9.60 Hymod AT 14.00 FRIT 3134 35.52 Potash Feldspar 18.00 OM #4 Ball Clay0.24 CaO 0.25 CaO
0.01 MgO 0.00 MgO 0.05 K2O 0.01 K2O 0.02 Na2O 0.06 Na2O 0.00 TiO2 0.00 TiO2 0.09 Al2O3 0.09 Al2O3 0.04 B2O3 0.05 B2O3 0.93 SiO2 0.95 SiO2 0.00 Fe2O3 0.00 Fe2O3I would really appreciate some pointers on where to research/how to assess the cause of the ?problem?.
Thanks